From c2c8187118c4bf2961aa175ff8667e1402a767c7 Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Wed, 21 Jun 2023 23:15:24 -0400
Subject: [PATCH 1/3] Fix test file name

It's UTF-8, not UFT-8.
---
 tests/lang/{parse-fail-uft8.nix => parse-fail-utf8.nix} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename tests/lang/{parse-fail-uft8.nix => parse-fail-utf8.nix} (100%)

diff --git a/tests/lang/parse-fail-uft8.nix b/tests/lang/parse-fail-utf8.nix
similarity index 100%
rename from tests/lang/parse-fail-uft8.nix
rename to tests/lang/parse-fail-utf8.nix

From c70484454f52a3bba994ac0c155b4a6f35a5013c Mon Sep 17 00:00:00 2001
From: Mathnerd314 <mathnerd314.gph+hs@gmail.com>
Date: Fri, 4 Sep 2015 14:23:08 -0600
Subject: [PATCH 2/3] Expanded test suite

* Lang now verifies errors and parse output

* Some new miscellaneous tests

* Easy way to update the tests

* Document workflow in manual

* Use `!` not `~` as separater char for sed

  It is confusing to use `~` when we are talking about paths and home
  directories!

* Test test suite itself (`test/lang-test/infra.sh`)

Additionally, run shellcheck on `tests/lang.sh` to help ensure it is
correct, now that is is more complex.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
---
 .gitignore                                    |   1 +
 doc/manual/src/contributing/testing.md        |  25 ++++
 tests/dependencies.sh                         |   3 +
 tests/lang-test-infra.sh                      |  86 ++++++++++++
 tests/lang.sh                                 | 123 +++++++++++++-----
 tests/lang/empty.exp                          |   0
 tests/lang/eval-fail-abort.err.exp            |  10 ++
 tests/lang/eval-fail-antiquoted-path.err.exp  |   1 +
 tests/lang/eval-fail-assert.err.exp           |  36 +++++
 tests/lang/eval-fail-bad-antiquote-1.err.exp  |  10 ++
 tests/lang/eval-fail-bad-antiquote-2.err.exp  |   1 +
 tests/lang/eval-fail-bad-antiquote-3.err.exp  |  10 ++
 ...al-fail-bad-string-interpolation-1.err.exp |  10 ++
 ...al-fail-bad-string-interpolation-2.err.exp |   1 +
 ...al-fail-bad-string-interpolation-3.err.exp |  10 ++
 tests/lang/eval-fail-blackhole.err.exp        |  18 +++
 tests/lang/eval-fail-deepseq.err.exp          |  26 ++++
 ...-foldlStrict-strict-op-application.err.exp |  38 ++++++
 .../eval-fail-fromTOML-timestamps.err.exp     |  12 ++
 tests/lang/eval-fail-hashfile-missing.err.exp |  19 +++
 tests/lang/eval-fail-list.err.exp             |  10 ++
 tests/lang/eval-fail-list.nix                 |   1 +
 tests/lang/eval-fail-missing-arg.err.exp      |  16 +++
 tests/lang/eval-fail-nonexist-path.err.exp    |   1 +
 tests/lang/eval-fail-path-slash.err.exp       |   8 ++
 tests/lang/eval-fail-recursion.err.exp        |  16 +++
 tests/lang/eval-fail-recursion.nix            |   1 +
 tests/lang/eval-fail-remove.err.exp           |  19 +++
 tests/lang/eval-fail-scope-5.err.exp          |  36 +++++
 tests/lang/eval-fail-seq.err.exp              |  18 +++
 tests/lang/eval-fail-set-override.err.exp     |   6 +
 tests/lang/eval-fail-set-override.nix         |   1 +
 tests/lang/eval-fail-set.err.exp              |   7 +
 tests/lang/eval-fail-set.nix                  |   1 +
 tests/lang/eval-fail-substring.err.exp        |  12 ++
 tests/lang/eval-fail-to-path.err.exp          |  14 ++
 tests/lang/eval-fail-undeclared-arg.err.exp   |  17 +++
 tests/lang/eval-okay-fromjson.nix             |  14 +-
 tests/lang/eval-okay-overrides.nix            |   2 +-
 tests/lang/eval-okay-print.err.exp            |   1 +
 tests/lang/eval-okay-print.exp                |   1 +
 tests/lang/eval-okay-print.nix                |   1 +
 tests/lang/eval-okay-search-path.flags        |   2 +-
 tests/lang/framework.sh                       |  33 +++++
 tests/lang/parse-fail-dup-attrs-1.err.exp     |   7 +
 tests/lang/parse-fail-dup-attrs-2.err.exp     |   7 +
 tests/lang/parse-fail-dup-attrs-3.err.exp     |   7 +
 tests/lang/parse-fail-dup-attrs-4.err.exp     |   7 +
 tests/lang/parse-fail-dup-attrs-6.err.exp     |   1 +
 tests/lang/parse-fail-dup-attrs-7.err.exp     |   7 +
 tests/lang/parse-fail-dup-formals.err.exp     |   6 +
 tests/lang/parse-fail-eof-in-string.err.exp   |   7 +
 .../parse-fail-mixed-nested-attrs1.err.exp    |   8 ++
 .../parse-fail-mixed-nested-attrs2.err.exp    |   8 ++
 tests/lang/parse-fail-patterns-1.err.exp      |   7 +
 .../parse-fail-regression-20060610.err.exp    |   8 ++
 tests/lang/parse-fail-undef-var-2.err.exp     |   7 +
 tests/lang/parse-fail-undef-var.err.exp       |   7 +
 tests/lang/parse-fail-utf8.err.exp            |   6 +
 tests/lang/parse-okay-1.exp                   |   1 +
 tests/lang/parse-okay-crlf.exp                |   1 +
 tests/lang/parse-okay-dup-attrs-5.exp         |   1 +
 tests/lang/parse-okay-dup-attrs-6.exp         |   1 +
 .../lang/parse-okay-mixed-nested-attrs-1.exp  |   1 +
 .../lang/parse-okay-mixed-nested-attrs-2.exp  |   1 +
 .../lang/parse-okay-mixed-nested-attrs-3.exp  |   1 +
 tests/lang/parse-okay-regression-20041027.exp |   1 +
 tests/lang/parse-okay-regression-751.exp      |   1 +
 tests/lang/parse-okay-subversion.exp          |   1 +
 tests/lang/parse-okay-url.exp                 |   1 +
 tests/local.mk                                |   1 +
 tests/misc.sh                                 |   6 +
 tests/restricted.sh                           |   2 +
 73 files changed, 762 insertions(+), 36 deletions(-)
 create mode 100644 tests/lang-test-infra.sh
 mode change 100644 => 100755 tests/lang.sh
 create mode 100644 tests/lang/empty.exp
 create mode 100644 tests/lang/eval-fail-abort.err.exp
 create mode 100644 tests/lang/eval-fail-antiquoted-path.err.exp
 create mode 100644 tests/lang/eval-fail-assert.err.exp
 create mode 100644 tests/lang/eval-fail-bad-antiquote-1.err.exp
 create mode 100644 tests/lang/eval-fail-bad-antiquote-2.err.exp
 create mode 100644 tests/lang/eval-fail-bad-antiquote-3.err.exp
 create mode 100644 tests/lang/eval-fail-bad-string-interpolation-1.err.exp
 create mode 100644 tests/lang/eval-fail-bad-string-interpolation-2.err.exp
 create mode 100644 tests/lang/eval-fail-bad-string-interpolation-3.err.exp
 create mode 100644 tests/lang/eval-fail-blackhole.err.exp
 create mode 100644 tests/lang/eval-fail-deepseq.err.exp
 create mode 100644 tests/lang/eval-fail-foldlStrict-strict-op-application.err.exp
 create mode 100644 tests/lang/eval-fail-fromTOML-timestamps.err.exp
 create mode 100644 tests/lang/eval-fail-hashfile-missing.err.exp
 create mode 100644 tests/lang/eval-fail-list.err.exp
 create mode 100644 tests/lang/eval-fail-list.nix
 create mode 100644 tests/lang/eval-fail-missing-arg.err.exp
 create mode 100644 tests/lang/eval-fail-nonexist-path.err.exp
 create mode 100644 tests/lang/eval-fail-path-slash.err.exp
 create mode 100644 tests/lang/eval-fail-recursion.err.exp
 create mode 100644 tests/lang/eval-fail-recursion.nix
 create mode 100644 tests/lang/eval-fail-remove.err.exp
 create mode 100644 tests/lang/eval-fail-scope-5.err.exp
 create mode 100644 tests/lang/eval-fail-seq.err.exp
 create mode 100644 tests/lang/eval-fail-set-override.err.exp
 create mode 100644 tests/lang/eval-fail-set-override.nix
 create mode 100644 tests/lang/eval-fail-set.err.exp
 create mode 100644 tests/lang/eval-fail-set.nix
 create mode 100644 tests/lang/eval-fail-substring.err.exp
 create mode 100644 tests/lang/eval-fail-to-path.err.exp
 create mode 100644 tests/lang/eval-fail-undeclared-arg.err.exp
 create mode 100644 tests/lang/eval-okay-print.err.exp
 create mode 100644 tests/lang/eval-okay-print.exp
 create mode 100644 tests/lang/eval-okay-print.nix
 create mode 100644 tests/lang/framework.sh
 create mode 100644 tests/lang/parse-fail-dup-attrs-1.err.exp
 create mode 100644 tests/lang/parse-fail-dup-attrs-2.err.exp
 create mode 100644 tests/lang/parse-fail-dup-attrs-3.err.exp
 create mode 100644 tests/lang/parse-fail-dup-attrs-4.err.exp
 create mode 100644 tests/lang/parse-fail-dup-attrs-6.err.exp
 create mode 100644 tests/lang/parse-fail-dup-attrs-7.err.exp
 create mode 100644 tests/lang/parse-fail-dup-formals.err.exp
 create mode 100644 tests/lang/parse-fail-eof-in-string.err.exp
 create mode 100644 tests/lang/parse-fail-mixed-nested-attrs1.err.exp
 create mode 100644 tests/lang/parse-fail-mixed-nested-attrs2.err.exp
 create mode 100644 tests/lang/parse-fail-patterns-1.err.exp
 create mode 100644 tests/lang/parse-fail-regression-20060610.err.exp
 create mode 100644 tests/lang/parse-fail-undef-var-2.err.exp
 create mode 100644 tests/lang/parse-fail-undef-var.err.exp
 create mode 100644 tests/lang/parse-fail-utf8.err.exp
 create mode 100644 tests/lang/parse-okay-1.exp
 create mode 100644 tests/lang/parse-okay-crlf.exp
 create mode 100644 tests/lang/parse-okay-dup-attrs-5.exp
 create mode 100644 tests/lang/parse-okay-dup-attrs-6.exp
 create mode 100644 tests/lang/parse-okay-mixed-nested-attrs-1.exp
 create mode 100644 tests/lang/parse-okay-mixed-nested-attrs-2.exp
 create mode 100644 tests/lang/parse-okay-mixed-nested-attrs-3.exp
 create mode 100644 tests/lang/parse-okay-regression-20041027.exp
 create mode 100644 tests/lang/parse-okay-regression-751.exp
 create mode 100644 tests/lang/parse-okay-subversion.exp
 create mode 100644 tests/lang/parse-okay-url.exp

diff --git a/.gitignore b/.gitignore
index 969194650..93a9ff9ae 100644
--- a/.gitignore
+++ b/.gitignore
@@ -95,6 +95,7 @@ perl/Makefile.config
 # /tests/lang/
 /tests/lang/*.out
 /tests/lang/*.out.xml
+/tests/lang/*.err
 /tests/lang/*.ast
 
 /perl/lib/Nix/Config.pm
diff --git a/doc/manual/src/contributing/testing.md b/doc/manual/src/contributing/testing.md
index e5f80a928..a5253997d 100644
--- a/doc/manual/src/contributing/testing.md
+++ b/doc/manual/src/contributing/testing.md
@@ -86,6 +86,31 @@ GNU gdb (GDB) 12.1
 One can debug the Nix invocation in all the usual ways.
 For example, enter `run` to start the Nix invocation.
 
+### Characterization testing
+
+Occasionally, Nix utilizes a technique called [Characterization Testing](https://en.wikipedia.org/wiki/Characterization_test) as part of the functional tests.
+This technique is to include the exact output/behavior of a former version of Nix in a test in order to check that Nix continues to produce the same behavior going forward.
+
+For example, this technique is used for the language tests, to check both the printed final value if evaluation was successful, and any errors and warnings encountered.
+
+It is frequently useful to regenerate the expected output.
+To do that, rerun the failed test with `_NIX_TEST_ACCEPT=1`.
+(At least, this is the convention we've used for `tests/lang.sh`.
+If we add more characterization testing we should always strive to be consistent.)
+
+An interesting situation to document is the case when these tests are "overfitted".
+The language tests are, again, an example of this.
+The expected successful output of evaluation is supposed to be highly stable – we do not intend to make breaking changes to (the stable parts of) the Nix language.
+However, the errors and warnings during evaluation (successful or not) are not stable in this way.
+We are free to change how they are displayed at any time.
+
+It may be surprising that we would test non-normative behavior like diagnostic outputs.
+Diagnostic outputs are indeed not a stable interface, but they still are important to users.
+By recording the expected output, the test suite guards against accidental changes, and ensure the *result* (not just the code that implements it) of the diagnostic code paths are under code review.
+Regressions are caught, and improvements always show up in code review.
+
+To ensure that characterization testing doesn't make it harder to intentionally change these interfaces, there always must be an easy way to regenerate the expected output, as we do with `_NIX_TEST_ACCEPT=1`.
+
 ## Integration tests
 
 The integration tests are defined in the Nix flake under the `hydraJobs.tests` attribute.
diff --git a/tests/dependencies.sh b/tests/dependencies.sh
index f9da0c6bc..d5cd30396 100644
--- a/tests/dependencies.sh
+++ b/tests/dependencies.sh
@@ -15,6 +15,9 @@ if test -n "$dot"; then
     $dot < $TEST_ROOT/graph
 fi
 
+# Test GraphML graph generation
+nix-store -q --graphml "$drvPath" > $TEST_ROOT/graphml
+
 outPath=$(nix-store -rvv "$drvPath") || fail "build failed"
 
 # Test Graphviz graph generation.
diff --git a/tests/lang-test-infra.sh b/tests/lang-test-infra.sh
new file mode 100644
index 000000000..30da8977b
--- /dev/null
+++ b/tests/lang-test-infra.sh
@@ -0,0 +1,86 @@
+# Test the function for lang.sh
+source common.sh
+
+source lang/framework.sh
+
+# We are testing this, so don't want outside world to affect us.
+unset _NIX_TEST_ACCEPT
+
+# We'll only modify this in subshells so we don't need to reset it.
+badDiff=0
+
+# matches non-empty
+echo Hi! > "$TEST_ROOT/got"
+cp "$TEST_ROOT/got" "$TEST_ROOT/expected"
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 0 ))
+)
+
+# matches empty, non-existant file is the same as empty file
+echo -n > "$TEST_ROOT/got"
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/does-not-exist"
+  (( "$badDiff" == 0 ))
+)
+
+# doesn't matches non-empty, non-existant file is the same as empty file
+echo Hi! > "$TEST_ROOT/got"
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/does-not-exist"
+  (( "$badDiff" == 1 ))
+)
+
+# doesn't match, `badDiff` set, file unchanged
+echo Hi! > "$TEST_ROOT/got"
+echo Bye! > "$TEST_ROOT/expected"
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 1 ))
+)
+[[ "$(echo Bye! )" == $(< "$TEST_ROOT/expected") ]]
+
+# _NIX_TEST_ACCEPT=1 matches non-empty
+echo Hi! > "$TEST_ROOT/got"
+cp "$TEST_ROOT/got" "$TEST_ROOT/expected"
+(
+  _NIX_TEST_ACCEPT=1 diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 0 ))
+)
+
+# _NIX_TEST_ACCEPT doesn't match, `badDiff=1` set, file changed (was previously non-empty)
+echo Hi! > "$TEST_ROOT/got"
+echo Bye! > "$TEST_ROOT/expected"
+(
+  _NIX_TEST_ACCEPT=1 diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 1 ))
+)
+[[ "$(echo Hi! )" == $(< "$TEST_ROOT/expected") ]]
+# second time succeeds
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 0 ))
+)
+
+# _NIX_TEST_ACCEPT matches empty, non-existant file not created
+echo -n > "$TEST_ROOT/got"
+(
+  _NIX_TEST_ACCEPT=1 diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/does-not-exists"
+  (( "$badDiff" == 0 ))
+)
+[[ ! -f "$TEST_ROOT/does-not-exist" ]]
+
+# _NIX_TEST_ACCEPT doesn't match, output empty, file deleted
+echo -n > "$TEST_ROOT/got"
+echo Bye! > "$TEST_ROOT/expected"
+badDiff=0
+(
+  _NIX_TEST_ACCEPT=1 diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 1 ))
+)
+[[ ! -f "$TEST_ROOT/expected" ]]
+# second time succeeds
+(
+  diffAndAcceptInner test "$TEST_ROOT/got" "$TEST_ROOT/expected"
+  (( "$badDiff" == 0 ))
+)
diff --git a/tests/lang.sh b/tests/lang.sh
old mode 100644
new mode 100755
index 8170cb39d..bfb942d3d
--- a/tests/lang.sh
+++ b/tests/lang.sh
@@ -1,5 +1,17 @@
 source common.sh
 
+set -o pipefail
+
+source lang/framework.sh
+
+# specialize function a bit
+function diffAndAccept() {
+    local -r testName="$1"
+    local -r got="lang/$testName.$2"
+    local -r expected="lang/$testName.$3"
+    diffAndAcceptInner "$testName" "$got" "$expected"
+}
+
 export TEST_VAR=foo # for eval-okay-getenv.nix
 export NIX_REMOTE=dummy://
 export NIX_STORE_DIR=/nix/store
@@ -20,63 +32,114 @@ nix-instantiate --eval -E 'let x = { repeating = x; tracing = builtins.trace x t
 
 set +x
 
-fail=0
+badDiff=0
+badExitCode=0
 
 for i in lang/parse-fail-*.nix; do
     echo "parsing $i (should fail)";
-    i=$(basename $i .nix)
-    if ! expect 1 nix-instantiate --parse - < lang/$i.nix; then
+    i=$(basename "$i" .nix)
+    if expectStderr 1 nix-instantiate --parse - < "lang/$i.nix" > "lang/$i.err"
+    then
+        diffAndAccept "$i" err err.exp
+    else
         echo "FAIL: $i shouldn't parse"
-        fail=1
+        badExitCode=1
     fi
 done
 
 for i in lang/parse-okay-*.nix; do
     echo "parsing $i (should succeed)";
-    i=$(basename $i .nix)
-    if ! expect 0 nix-instantiate --parse - < lang/$i.nix > lang/$i.out; then
+    i=$(basename "$i" .nix)
+    if
+        expect 0 nix-instantiate --parse - < "lang/$i.nix" \
+            1> >(sed "s!$(pwd)!/pwd!g" > "lang/$i.out") \
+            2> >(sed "s!$(pwd)!/pwd!g" > "lang/$i.err")
+    then
+        diffAndAccept "$i" out exp
+        diffAndAccept "$i" err err.exp
+    else
         echo "FAIL: $i should parse"
-        fail=1
+        badExitCode=1
     fi
 done
 
 for i in lang/eval-fail-*.nix; do
     echo "evaluating $i (should fail)";
-    i=$(basename $i .nix)
-    if ! expect 1 nix-instantiate --eval lang/$i.nix; then
+    i=$(basename "$i" .nix)
+    if
+        expectStderr 1 nix-instantiate --show-trace "lang/$i.nix" \
+            | sed "s!$(pwd)!/pwd!g" > "lang/$i.err"
+    then
+        diffAndAccept "$i" err err.exp
+    else
         echo "FAIL: $i shouldn't evaluate"
-        fail=1
+        badExitCode=1
     fi
 done
 
 for i in lang/eval-okay-*.nix; do
     echo "evaluating $i (should succeed)";
-    i=$(basename $i .nix)
+    i=$(basename "$i" .nix)
 
-    if test -e lang/$i.exp; then
-        flags=
-        if test -e lang/$i.flags; then
-            flags=$(cat lang/$i.flags)
-        fi
-        if ! expect 0 env NIX_PATH=lang/dir3:lang/dir4 HOME=/fake-home nix-instantiate $flags --eval --strict lang/$i.nix > lang/$i.out; then
+    if test -e "lang/$i.exp.xml"; then
+        if expect 0 nix-instantiate --eval --xml --no-location --strict \
+                "lang/$i.nix" > "lang/$i.out.xml"
+        then
+            diffAndAccept "$i" out.xml exp.xml
+        else
             echo "FAIL: $i should evaluate"
-            fail=1
-        elif ! diff <(< lang/$i.out sed -e "s|$(pwd)|/pwd|g") lang/$i.exp; then
-            echo "FAIL: evaluation result of $i not as expected"
-            fail=1
+            badExitCode=1
+        fi
+    elif test ! -e "lang/$i.exp-disabled"; then
+        declare -a flags=()
+        if test -e "lang/$i.flags"; then
+            read -r -a flags < "lang/$i.flags"
         fi
-    fi
 
-    if test -e lang/$i.exp.xml; then
-        if ! expect 0 nix-instantiate --eval --xml --no-location --strict \
-                lang/$i.nix > lang/$i.out.xml; then
+        if
+            expect 0 env \
+                NIX_PATH=lang/dir3:lang/dir4 \
+                HOME=/fake-home \
+                nix-instantiate "${flags[@]}" --eval --strict "lang/$i.nix" \
+                1> "lang/$i.out" \
+                2> "lang/$i.err"
+        then
+            sed -i "s!$(pwd)!/pwd!g" "lang/$i.out" "lang/$i.err"
+            diffAndAccept "$i" out exp
+            diffAndAccept "$i" err err.exp
+        else
             echo "FAIL: $i should evaluate"
-            fail=1
-        elif ! cmp -s lang/$i.out.xml lang/$i.exp.xml; then
-            echo "FAIL: XML evaluation result of $i not as expected"
-            fail=1
+            badExitCode=1
         fi
     fi
 done
 
-exit $fail
+if test -n "${_NIX_TEST_ACCEPT-}"; then
+    if (( "$badDiff" )); then
+        echo 'Output did mot match, but accepted output as the persisted expected output.'
+        echo 'That means the next time the tests are run, they should pass.'
+    else
+        echo 'NOTE: Environment variable _NIX_TEST_ACCEPT is defined,'
+        echo 'indicating the unexpected output should be accepted as the expected output going forward,'
+        echo 'but no tests had unexpected output so there was no expected output to update.'
+    fi
+    if (( "$badExitCode" )); then
+        exit "$badExitCode"
+    else
+        skipTest "regenerating golden masters"
+    fi
+else
+    if (( "$badDiff" )); then
+        echo ''
+        echo 'You can rerun this test with:'
+        echo ''
+        echo '    _NIX_TEST_ACCEPT=1 make tests/lang.sh.test'
+        echo ''
+        echo 'to regenerate the files containing the expected output,'
+        echo 'and then view the git diff to decide whether a change is'
+        echo 'good/intentional or bad/unintentional.'
+        echo 'If the diff contains arbitrary or impure information,'
+        echo 'please improve the normalization that the test applies to the output.'
+    fi
+    exit $(( "$badExitCode" + "$badDiff" ))
+fi
diff --git a/tests/lang/empty.exp b/tests/lang/empty.exp
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/lang/eval-fail-abort.err.exp b/tests/lang/eval-fail-abort.err.exp
new file mode 100644
index 000000000..345232d3f
--- /dev/null
+++ b/tests/lang/eval-fail-abort.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while calling the 'abort' builtin
+
+         at /pwd/lang/eval-fail-abort.nix:1:14:
+
+            1| if true then abort "this should fail" else 1
+             |              ^
+            2|
+
+       error: evaluation aborted with the following error message: 'this should fail'
diff --git a/tests/lang/eval-fail-antiquoted-path.err.exp b/tests/lang/eval-fail-antiquoted-path.err.exp
new file mode 100644
index 000000000..425deba42
--- /dev/null
+++ b/tests/lang/eval-fail-antiquoted-path.err.exp
@@ -0,0 +1 @@
+error: getting attributes of path ‘PWD/lang/fnord’: No such file or directory
diff --git a/tests/lang/eval-fail-assert.err.exp b/tests/lang/eval-fail-assert.err.exp
new file mode 100644
index 000000000..aeecd8167
--- /dev/null
+++ b/tests/lang/eval-fail-assert.err.exp
@@ -0,0 +1,36 @@
+error:
+       … while evaluating the attribute 'body'
+
+         at /pwd/lang/eval-fail-assert.nix:4:3:
+
+            3|
+            4|   body = x "x";
+             |   ^
+            5| }
+
+       … from call site
+
+         at /pwd/lang/eval-fail-assert.nix:4:10:
+
+            3|
+            4|   body = x "x";
+             |          ^
+            5| }
+
+       … while calling 'x'
+
+         at /pwd/lang/eval-fail-assert.nix:2:7:
+
+            1| let {
+            2|   x = arg: assert arg == "y"; 123;
+             |       ^
+            3|
+
+       error: assertion '(arg == "y")' failed
+
+       at /pwd/lang/eval-fail-assert.nix:2:12:
+
+            1| let {
+            2|   x = arg: assert arg == "y"; 123;
+             |            ^
+            3|
diff --git a/tests/lang/eval-fail-bad-antiquote-1.err.exp b/tests/lang/eval-fail-bad-antiquote-1.err.exp
new file mode 100644
index 000000000..cf94f53bc
--- /dev/null
+++ b/tests/lang/eval-fail-bad-antiquote-1.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while evaluating a path segment
+
+         at /pwd/lang/eval-fail-bad-antiquote-1.nix:1:2:
+
+            1| "${x: x}"
+             |  ^
+            2|
+
+       error: cannot coerce a function to a string
diff --git a/tests/lang/eval-fail-bad-antiquote-2.err.exp b/tests/lang/eval-fail-bad-antiquote-2.err.exp
new file mode 100644
index 000000000..c8fe39d12
--- /dev/null
+++ b/tests/lang/eval-fail-bad-antiquote-2.err.exp
@@ -0,0 +1 @@
+error: operation 'addToStoreFromDump' is not supported by store 'dummy'
diff --git a/tests/lang/eval-fail-bad-antiquote-3.err.exp b/tests/lang/eval-fail-bad-antiquote-3.err.exp
new file mode 100644
index 000000000..fbefbc826
--- /dev/null
+++ b/tests/lang/eval-fail-bad-antiquote-3.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while evaluating a path segment
+
+         at /pwd/lang/eval-fail-bad-antiquote-3.nix:1:3:
+
+            1| ''${x: x}''
+             |   ^
+            2|
+
+       error: cannot coerce a function to a string
diff --git a/tests/lang/eval-fail-bad-string-interpolation-1.err.exp b/tests/lang/eval-fail-bad-string-interpolation-1.err.exp
new file mode 100644
index 000000000..eb73e9a52
--- /dev/null
+++ b/tests/lang/eval-fail-bad-string-interpolation-1.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while evaluating a path segment
+
+         at /pwd/lang/eval-fail-bad-string-interpolation-1.nix:1:2:
+
+            1| "${x: x}"
+             |  ^
+            2|
+
+       error: cannot coerce a function to a string
diff --git a/tests/lang/eval-fail-bad-string-interpolation-2.err.exp b/tests/lang/eval-fail-bad-string-interpolation-2.err.exp
new file mode 100644
index 000000000..c8fe39d12
--- /dev/null
+++ b/tests/lang/eval-fail-bad-string-interpolation-2.err.exp
@@ -0,0 +1 @@
+error: operation 'addToStoreFromDump' is not supported by store 'dummy'
diff --git a/tests/lang/eval-fail-bad-string-interpolation-3.err.exp b/tests/lang/eval-fail-bad-string-interpolation-3.err.exp
new file mode 100644
index 000000000..ac14f329b
--- /dev/null
+++ b/tests/lang/eval-fail-bad-string-interpolation-3.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while evaluating a path segment
+
+         at /pwd/lang/eval-fail-bad-string-interpolation-3.nix:1:3:
+
+            1| ''${x: x}''
+             |   ^
+            2|
+
+       error: cannot coerce a function to a string
diff --git a/tests/lang/eval-fail-blackhole.err.exp b/tests/lang/eval-fail-blackhole.err.exp
new file mode 100644
index 000000000..f0618d8ac
--- /dev/null
+++ b/tests/lang/eval-fail-blackhole.err.exp
@@ -0,0 +1,18 @@
+error:
+       … while evaluating the attribute 'body'
+
+         at /pwd/lang/eval-fail-blackhole.nix:2:3:
+
+            1| let {
+            2|   body = x;
+             |   ^
+            3|   x = y;
+
+       error: infinite recursion encountered
+
+       at /pwd/lang/eval-fail-blackhole.nix:3:7:
+
+            2|   body = x;
+            3|   x = y;
+             |       ^
+            4|   y = x;
diff --git a/tests/lang/eval-fail-deepseq.err.exp b/tests/lang/eval-fail-deepseq.err.exp
new file mode 100644
index 000000000..5e204ba73
--- /dev/null
+++ b/tests/lang/eval-fail-deepseq.err.exp
@@ -0,0 +1,26 @@
+error:
+       … while calling the 'deepSeq' builtin
+
+         at /pwd/lang/eval-fail-deepseq.nix:1:1:
+
+            1| builtins.deepSeq { x = abort "foo"; } 456
+             | ^
+            2|
+
+       … while evaluating the attribute 'x'
+
+         at /pwd/lang/eval-fail-deepseq.nix:1:20:
+
+            1| builtins.deepSeq { x = abort "foo"; } 456
+             |                    ^
+            2|
+
+       … while calling the 'abort' builtin
+
+         at /pwd/lang/eval-fail-deepseq.nix:1:24:
+
+            1| builtins.deepSeq { x = abort "foo"; } 456
+             |                        ^
+            2|
+
+       error: evaluation aborted with the following error message: 'foo'
diff --git a/tests/lang/eval-fail-foldlStrict-strict-op-application.err.exp b/tests/lang/eval-fail-foldlStrict-strict-op-application.err.exp
new file mode 100644
index 000000000..0069285fb
--- /dev/null
+++ b/tests/lang/eval-fail-foldlStrict-strict-op-application.err.exp
@@ -0,0 +1,38 @@
+error:
+       … while calling the 'foldl'' builtin
+
+         at /pwd/lang/eval-fail-foldlStrict-strict-op-application.nix:2:1:
+
+            1| # Tests that the result of applying op is forced even if the value is never used
+            2| builtins.foldl'
+             | ^
+            3|   (_: f: f null)
+
+       … while calling anonymous lambda
+
+         at /pwd/lang/eval-fail-foldlStrict-strict-op-application.nix:3:7:
+
+            2| builtins.foldl'
+            3|   (_: f: f null)
+             |       ^
+            4|   null
+
+       … from call site
+
+         at /pwd/lang/eval-fail-foldlStrict-strict-op-application.nix:3:10:
+
+            2| builtins.foldl'
+            3|   (_: f: f null)
+             |          ^
+            4|   null
+
+       … while calling anonymous lambda
+
+         at /pwd/lang/eval-fail-foldlStrict-strict-op-application.nix:5:6:
+
+            4|   null
+            5|   [ (_: throw "Not the final value, but is still forced!") (_: 23) ]
+             |      ^
+            6|
+
+       error: Not the final value, but is still forced!
diff --git a/tests/lang/eval-fail-fromTOML-timestamps.err.exp b/tests/lang/eval-fail-fromTOML-timestamps.err.exp
new file mode 100644
index 000000000..f6bd19f5a
--- /dev/null
+++ b/tests/lang/eval-fail-fromTOML-timestamps.err.exp
@@ -0,0 +1,12 @@
+error:
+       … while calling the 'fromTOML' builtin
+
+         at /pwd/lang/eval-fail-fromTOML-timestamps.nix:1:1:
+
+            1| builtins.fromTOML ''
+             | ^
+            2|   key = "value"
+
+       error: while parsing a TOML string: Dates and times are not supported
+
+       at «none»:0: (source not available)
diff --git a/tests/lang/eval-fail-hashfile-missing.err.exp b/tests/lang/eval-fail-hashfile-missing.err.exp
new file mode 100644
index 000000000..8e77dec1e
--- /dev/null
+++ b/tests/lang/eval-fail-hashfile-missing.err.exp
@@ -0,0 +1,19 @@
+error:
+       … while calling the 'toString' builtin
+
+         at /pwd/lang/eval-fail-hashfile-missing.nix:4:3:
+
+            3| in
+            4|   toString (builtins.concatLists (map (hash: map (builtins.hashFile hash) paths) ["md5" "sha1" "sha256" "sha512"]))
+             |   ^
+            5|
+
+       … while evaluating the first argument passed to builtins.toString
+
+         at «none»:0: (source not available)
+
+       … while calling the 'hashFile' builtin
+
+         at «none»:0: (source not available)
+
+       error: opening file '/pwd/lang/this-file-is-definitely-not-there-7392097': No such file or directory
diff --git a/tests/lang/eval-fail-list.err.exp b/tests/lang/eval-fail-list.err.exp
new file mode 100644
index 000000000..24d682118
--- /dev/null
+++ b/tests/lang/eval-fail-list.err.exp
@@ -0,0 +1,10 @@
+error:
+       … while evaluating one of the elements to concatenate
+
+         at /pwd/lang/eval-fail-list.nix:1:2:
+
+            1| 8++1
+             |  ^
+            2|
+
+       error: value is an integer while a list was expected
diff --git a/tests/lang/eval-fail-list.nix b/tests/lang/eval-fail-list.nix
new file mode 100644
index 000000000..fa749f2f7
--- /dev/null
+++ b/tests/lang/eval-fail-list.nix
@@ -0,0 +1 @@
+8++1
diff --git a/tests/lang/eval-fail-missing-arg.err.exp b/tests/lang/eval-fail-missing-arg.err.exp
new file mode 100644
index 000000000..61fabf0d5
--- /dev/null
+++ b/tests/lang/eval-fail-missing-arg.err.exp
@@ -0,0 +1,16 @@
+error:
+       … from call site
+
+         at /pwd/lang/eval-fail-missing-arg.nix:1:1:
+
+            1| ({x, y, z}: x + y + z) {x = "foo"; z = "bar";}
+             | ^
+            2|
+
+       error: function 'anonymous lambda' called without required argument 'y'
+
+       at /pwd/lang/eval-fail-missing-arg.nix:1:2:
+
+            1| ({x, y, z}: x + y + z) {x = "foo"; z = "bar";}
+             |  ^
+            2|
diff --git a/tests/lang/eval-fail-nonexist-path.err.exp b/tests/lang/eval-fail-nonexist-path.err.exp
new file mode 100644
index 000000000..c8fe39d12
--- /dev/null
+++ b/tests/lang/eval-fail-nonexist-path.err.exp
@@ -0,0 +1 @@
+error: operation 'addToStoreFromDump' is not supported by store 'dummy'
diff --git a/tests/lang/eval-fail-path-slash.err.exp b/tests/lang/eval-fail-path-slash.err.exp
new file mode 100644
index 000000000..f0011c97f
--- /dev/null
+++ b/tests/lang/eval-fail-path-slash.err.exp
@@ -0,0 +1,8 @@
+error: path has a trailing slash
+
+       at /pwd/lang/eval-fail-path-slash.nix:6:12:
+
+            5| # and https://nixos.org/nix-dev/2016-June/020829.html
+            6| /nix/store/
+             |            ^
+            7|
diff --git a/tests/lang/eval-fail-recursion.err.exp b/tests/lang/eval-fail-recursion.err.exp
new file mode 100644
index 000000000..af64133cb
--- /dev/null
+++ b/tests/lang/eval-fail-recursion.err.exp
@@ -0,0 +1,16 @@
+error:
+       … in the right operand of the update (//) operator
+
+         at /pwd/lang/eval-fail-recursion.nix:1:12:
+
+            1| let a = {} // a; in a.foo
+             |            ^
+            2|
+
+       error: infinite recursion encountered
+
+       at /pwd/lang/eval-fail-recursion.nix:1:15:
+
+            1| let a = {} // a; in a.foo
+             |               ^
+            2|
diff --git a/tests/lang/eval-fail-recursion.nix b/tests/lang/eval-fail-recursion.nix
new file mode 100644
index 000000000..075b5ed06
--- /dev/null
+++ b/tests/lang/eval-fail-recursion.nix
@@ -0,0 +1 @@
+let a = {} // a; in a.foo
diff --git a/tests/lang/eval-fail-remove.err.exp b/tests/lang/eval-fail-remove.err.exp
new file mode 100644
index 000000000..e82cdac98
--- /dev/null
+++ b/tests/lang/eval-fail-remove.err.exp
@@ -0,0 +1,19 @@
+error:
+       … while evaluating the attribute 'body'
+
+         at /pwd/lang/eval-fail-remove.nix:4:3:
+
+            3|
+            4|   body = (removeAttrs attrs ["x"]).x;
+             |   ^
+            5| }
+
+       error: attribute 'x' missing
+
+       at /pwd/lang/eval-fail-remove.nix:4:10:
+
+            3|
+            4|   body = (removeAttrs attrs ["x"]).x;
+             |          ^
+            5| }
+       Did you mean y?
diff --git a/tests/lang/eval-fail-scope-5.err.exp b/tests/lang/eval-fail-scope-5.err.exp
new file mode 100644
index 000000000..22b6166f8
--- /dev/null
+++ b/tests/lang/eval-fail-scope-5.err.exp
@@ -0,0 +1,36 @@
+error:
+       … while evaluating the attribute 'body'
+
+         at /pwd/lang/eval-fail-scope-5.nix:8:3:
+
+            7|
+            8|   body = f {};
+             |   ^
+            9|
+
+       … from call site
+
+         at /pwd/lang/eval-fail-scope-5.nix:8:10:
+
+            7|
+            8|   body = f {};
+             |          ^
+            9|
+
+       … while calling 'f'
+
+         at /pwd/lang/eval-fail-scope-5.nix:6:7:
+
+            5|
+            6|   f = {x ? y, y ? x}: x + y;
+             |       ^
+            7|
+
+       error: infinite recursion encountered
+
+       at /pwd/lang/eval-fail-scope-5.nix:6:12:
+
+            5|
+            6|   f = {x ? y, y ? x}: x + y;
+             |            ^
+            7|
diff --git a/tests/lang/eval-fail-seq.err.exp b/tests/lang/eval-fail-seq.err.exp
new file mode 100644
index 000000000..33a7e9491
--- /dev/null
+++ b/tests/lang/eval-fail-seq.err.exp
@@ -0,0 +1,18 @@
+error:
+       … while calling the 'seq' builtin
+
+         at /pwd/lang/eval-fail-seq.nix:1:1:
+
+            1| builtins.seq (abort "foo") 2
+             | ^
+            2|
+
+       … while calling the 'abort' builtin
+
+         at /pwd/lang/eval-fail-seq.nix:1:15:
+
+            1| builtins.seq (abort "foo") 2
+             |               ^
+            2|
+
+       error: evaluation aborted with the following error message: 'foo'
diff --git a/tests/lang/eval-fail-set-override.err.exp b/tests/lang/eval-fail-set-override.err.exp
new file mode 100644
index 000000000..beb29d678
--- /dev/null
+++ b/tests/lang/eval-fail-set-override.err.exp
@@ -0,0 +1,6 @@
+error:
+       … while evaluating the `__overrides` attribute
+
+         at «none»:0: (source not available)
+
+       error: value is an integer while a set was expected
diff --git a/tests/lang/eval-fail-set-override.nix b/tests/lang/eval-fail-set-override.nix
new file mode 100644
index 000000000..03551c186
--- /dev/null
+++ b/tests/lang/eval-fail-set-override.nix
@@ -0,0 +1 @@
+rec { __overrides = 1; }
diff --git a/tests/lang/eval-fail-set.err.exp b/tests/lang/eval-fail-set.err.exp
new file mode 100644
index 000000000..0d0140508
--- /dev/null
+++ b/tests/lang/eval-fail-set.err.exp
@@ -0,0 +1,7 @@
+error: undefined variable 'x'
+
+       at /pwd/lang/eval-fail-set.nix:1:3:
+
+            1| 8.x
+             |   ^
+            2|
diff --git a/tests/lang/eval-fail-set.nix b/tests/lang/eval-fail-set.nix
new file mode 100644
index 000000000..c6b7980b6
--- /dev/null
+++ b/tests/lang/eval-fail-set.nix
@@ -0,0 +1 @@
+8.x
diff --git a/tests/lang/eval-fail-substring.err.exp b/tests/lang/eval-fail-substring.err.exp
new file mode 100644
index 000000000..dc26a00bd
--- /dev/null
+++ b/tests/lang/eval-fail-substring.err.exp
@@ -0,0 +1,12 @@
+error:
+       … while calling the 'substring' builtin
+
+         at /pwd/lang/eval-fail-substring.nix:1:1:
+
+            1| builtins.substring (builtins.sub 0 1) 1 "x"
+             | ^
+            2|
+
+       error: negative start position in 'substring'
+
+       at «none»:0: (source not available)
diff --git a/tests/lang/eval-fail-to-path.err.exp b/tests/lang/eval-fail-to-path.err.exp
new file mode 100644
index 000000000..43ed2bdfc
--- /dev/null
+++ b/tests/lang/eval-fail-to-path.err.exp
@@ -0,0 +1,14 @@
+error:
+       … while calling the 'toPath' builtin
+
+         at /pwd/lang/eval-fail-to-path.nix:1:1:
+
+            1| builtins.toPath "foo/bar"
+             | ^
+            2|
+
+       … while evaluating the first argument passed to builtins.toPath
+
+         at «none»:0: (source not available)
+
+       error: string 'foo/bar' doesn't represent an absolute path
diff --git a/tests/lang/eval-fail-undeclared-arg.err.exp b/tests/lang/eval-fail-undeclared-arg.err.exp
new file mode 100644
index 000000000..30db743c7
--- /dev/null
+++ b/tests/lang/eval-fail-undeclared-arg.err.exp
@@ -0,0 +1,17 @@
+error:
+       … from call site
+
+         at /pwd/lang/eval-fail-undeclared-arg.nix:1:1:
+
+            1| ({x, z}: x + z) {x = "foo"; y = "bla"; z = "bar";}
+             | ^
+            2|
+
+       error: function 'anonymous lambda' called with unexpected argument 'y'
+
+       at /pwd/lang/eval-fail-undeclared-arg.nix:1:2:
+
+            1| ({x, z}: x + z) {x = "foo"; y = "bla"; z = "bar";}
+             |  ^
+            2|
+       Did you mean one of x or z?
diff --git a/tests/lang/eval-okay-fromjson.nix b/tests/lang/eval-okay-fromjson.nix
index e1c0f86cc..4c526b9ae 100644
--- a/tests/lang/eval-okay-fromjson.nix
+++ b/tests/lang/eval-okay-fromjson.nix
@@ -11,9 +11,12 @@ builtins.fromJSON
               "Width":  200,
               "Height": 250
           },
+          "Animated" : false,
+          "IDs": [116, 943, 234, 38793, true  ,false,null, -100],
+          "Escapes": "\"\\\/\t\n\r\t",
           "Subtitle" : false,
-          "Latitude":  46.2051,
-          "Longitude": 6.0723
+          "Latitude":  37.7668,
+          "Longitude": -122.3959
         }
     }
   ''
@@ -28,8 +31,11 @@ builtins.fromJSON
           Width = 200;
           Height = 250;
         };
+      Animated = false;
+      IDs = [ 116 943 234 38793 true false null (0-100) ];
+      Escapes = "\"\\\/\t\n\r\t";  # supported in JSON but not Nix: \b\f
       Subtitle = false;
-      Latitude = 46.2051;
-      Longitude = 6.0723;
+      Latitude = 37.7668;
+      Longitude = -122.3959;
     };
   }
diff --git a/tests/lang/eval-okay-overrides.nix b/tests/lang/eval-okay-overrides.nix
index 358742b36..719bdc9c0 100644
--- a/tests/lang/eval-okay-overrides.nix
+++ b/tests/lang/eval-okay-overrides.nix
@@ -1,6 +1,6 @@
 let
 
-  overrides = { a = 2; };
+  overrides = { a = 2; b = 3; };
 
 in (rec {
   __overrides = overrides;
diff --git a/tests/lang/eval-okay-print.err.exp b/tests/lang/eval-okay-print.err.exp
new file mode 100644
index 000000000..3fc99be3e
--- /dev/null
+++ b/tests/lang/eval-okay-print.err.exp
@@ -0,0 +1 @@
+trace: [ <CODE> ]
diff --git a/tests/lang/eval-okay-print.exp b/tests/lang/eval-okay-print.exp
new file mode 100644
index 000000000..0d960fb70
--- /dev/null
+++ b/tests/lang/eval-okay-print.exp
@@ -0,0 +1 @@
+[ null <PRIMOP> <PRIMOP-APP> <LAMBDA> [ [ «repeated» ] ] ]
diff --git a/tests/lang/eval-okay-print.nix b/tests/lang/eval-okay-print.nix
new file mode 100644
index 000000000..d36ba4da3
--- /dev/null
+++ b/tests/lang/eval-okay-print.nix
@@ -0,0 +1 @@
+with builtins; trace [(1+1)] [ null toString (deepSeq "x") (a: a) (let x=[x]; in x) ]
diff --git a/tests/lang/eval-okay-search-path.flags b/tests/lang/eval-okay-search-path.flags
index a28e68210..dfad1c611 100644
--- a/tests/lang/eval-okay-search-path.flags
+++ b/tests/lang/eval-okay-search-path.flags
@@ -1 +1 @@
--I lang/dir1 -I lang/dir2 -I dir5=lang/dir3
\ No newline at end of file
+-I lang/dir1 -I lang/dir2 -I dir5=lang/dir3
diff --git a/tests/lang/framework.sh b/tests/lang/framework.sh
new file mode 100644
index 000000000..d6499e0e9
--- /dev/null
+++ b/tests/lang/framework.sh
@@ -0,0 +1,33 @@
+# Golden test support
+#
+# Test that the output of the given test matches what is expected. If
+# `_NIX_TEST_ACCEPT` is non-empty also update the expected output so
+# that next time the test succeeds.
+function diffAndAcceptInner() {
+    local -r testName=$1
+    local -r got="$2"
+    local -r expected="$3"
+
+    # Absence of expected file indicates empty output expected.
+    if test -e "$expected"; then
+        local -r expectedOrEmpty="$expected"
+    else
+        local -r expectedOrEmpty=lang/empty.exp
+    fi
+
+    # Diff so we get a nice message
+    if ! diff "$got" "$expectedOrEmpty"; then
+        echo "FAIL: evaluation result of $testName not as expected"
+        badDiff=1
+    fi
+
+    # Update expected if `_NIX_TEST_ACCEPT` is non-empty.
+    if test -n "${_NIX_TEST_ACCEPT-}"; then
+        cp "$got" "$expected"
+        # Delete empty expected files to avoid bloating the repo with
+        # empty files.
+        if ! test -s "$expected"; then
+            rm "$expected"
+        fi
+    fi
+}
diff --git a/tests/lang/parse-fail-dup-attrs-1.err.exp b/tests/lang/parse-fail-dup-attrs-1.err.exp
new file mode 100644
index 000000000..4fe6b7a1f
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-1.err.exp
@@ -0,0 +1,7 @@
+error: attribute 'x' already defined at «stdin»:1:3
+
+       at «stdin»:3:3:
+
+            2|   y = 456;
+            3|   x = 789;
+             |   ^
diff --git a/tests/lang/parse-fail-dup-attrs-2.err.exp b/tests/lang/parse-fail-dup-attrs-2.err.exp
new file mode 100644
index 000000000..3aba2891f
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-2.err.exp
@@ -0,0 +1,7 @@
+error: attribute 'x' already defined at «stdin»:9:5
+
+       at «stdin»:10:17:
+
+            9|     x = 789;
+           10|     inherit (as) x;
+             |                 ^
diff --git a/tests/lang/parse-fail-dup-attrs-3.err.exp b/tests/lang/parse-fail-dup-attrs-3.err.exp
new file mode 100644
index 000000000..3aba2891f
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-3.err.exp
@@ -0,0 +1,7 @@
+error: attribute 'x' already defined at «stdin»:9:5
+
+       at «stdin»:10:17:
+
+            9|     x = 789;
+           10|     inherit (as) x;
+             |                 ^
diff --git a/tests/lang/parse-fail-dup-attrs-4.err.exp b/tests/lang/parse-fail-dup-attrs-4.err.exp
new file mode 100644
index 000000000..ff68446a1
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-4.err.exp
@@ -0,0 +1,7 @@
+error: attribute 'services.ssh.port' already defined at «stdin»:2:3
+
+       at «stdin»:3:3:
+
+            2|   services.ssh.port = 22;
+            3|   services.ssh.port = 23;
+             |   ^
diff --git a/tests/lang/parse-fail-dup-attrs-6.err.exp b/tests/lang/parse-fail-dup-attrs-6.err.exp
new file mode 100644
index 000000000..74823fc25
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-6.err.exp
@@ -0,0 +1 @@
+error: attribute ‘services.ssh’ at (string):3:3 already defined at (string):2:3
diff --git a/tests/lang/parse-fail-dup-attrs-7.err.exp b/tests/lang/parse-fail-dup-attrs-7.err.exp
new file mode 100644
index 000000000..512a499ca
--- /dev/null
+++ b/tests/lang/parse-fail-dup-attrs-7.err.exp
@@ -0,0 +1,7 @@
+error: attribute 'x' already defined at «stdin»:6:12
+
+       at «stdin»:7:12:
+
+            6|     inherit x;
+            7|     inherit x;
+             |            ^
diff --git a/tests/lang/parse-fail-dup-formals.err.exp b/tests/lang/parse-fail-dup-formals.err.exp
new file mode 100644
index 000000000..1d566fb33
--- /dev/null
+++ b/tests/lang/parse-fail-dup-formals.err.exp
@@ -0,0 +1,6 @@
+error: duplicate formal function argument 'x'
+
+       at «stdin»:1:8:
+
+            1| {x, y, x}: x
+             |        ^
diff --git a/tests/lang/parse-fail-eof-in-string.err.exp b/tests/lang/parse-fail-eof-in-string.err.exp
new file mode 100644
index 000000000..f9fa72312
--- /dev/null
+++ b/tests/lang/parse-fail-eof-in-string.err.exp
@@ -0,0 +1,7 @@
+error: syntax error, unexpected end of file, expecting '"'
+
+       at «stdin»:3:5:
+
+            2| # Note that this file must not end with a newline.
+            3| a 1"$
+             |     ^
diff --git a/tests/lang/parse-fail-mixed-nested-attrs1.err.exp b/tests/lang/parse-fail-mixed-nested-attrs1.err.exp
new file mode 100644
index 000000000..32f776795
--- /dev/null
+++ b/tests/lang/parse-fail-mixed-nested-attrs1.err.exp
@@ -0,0 +1,8 @@
+error: attribute 'z' already defined at «stdin»:3:16
+
+       at «stdin»:2:3:
+
+            1| {
+            2|   x.z = 3;
+             |   ^
+            3|   x = { y = 3; z = 3; };
diff --git a/tests/lang/parse-fail-mixed-nested-attrs2.err.exp b/tests/lang/parse-fail-mixed-nested-attrs2.err.exp
new file mode 100644
index 000000000..0437cd50c
--- /dev/null
+++ b/tests/lang/parse-fail-mixed-nested-attrs2.err.exp
@@ -0,0 +1,8 @@
+error: attribute 'y' already defined at «stdin»:3:9
+
+       at «stdin»:2:3:
+
+            1| {
+            2|   x.y.y = 3;
+             |   ^
+            3|   x = { y.y= 3; z = 3; };
diff --git a/tests/lang/parse-fail-patterns-1.err.exp b/tests/lang/parse-fail-patterns-1.err.exp
new file mode 100644
index 000000000..634a04aaa
--- /dev/null
+++ b/tests/lang/parse-fail-patterns-1.err.exp
@@ -0,0 +1,7 @@
+error: duplicate formal function argument 'args'
+
+       at «stdin»:1:1:
+
+            1| args@{args, x, y, z}: x
+             | ^
+            2|
diff --git a/tests/lang/parse-fail-regression-20060610.err.exp b/tests/lang/parse-fail-regression-20060610.err.exp
new file mode 100644
index 000000000..167d01e85
--- /dev/null
+++ b/tests/lang/parse-fail-regression-20060610.err.exp
@@ -0,0 +1,8 @@
+error: undefined variable 'gcc'
+
+       at «stdin»:8:12:
+
+            7|
+            8|   body = ({
+             |            ^
+            9|     inherit gcc;
diff --git a/tests/lang/parse-fail-undef-var-2.err.exp b/tests/lang/parse-fail-undef-var-2.err.exp
new file mode 100644
index 000000000..77c96bbd2
--- /dev/null
+++ b/tests/lang/parse-fail-undef-var-2.err.exp
@@ -0,0 +1,7 @@
+error: syntax error, unexpected ':', expecting '}'
+
+       at «stdin»:3:13:
+
+            2|
+            3|   f = {x, y :
+             |             ^
diff --git a/tests/lang/parse-fail-undef-var.err.exp b/tests/lang/parse-fail-undef-var.err.exp
new file mode 100644
index 000000000..48e88747f
--- /dev/null
+++ b/tests/lang/parse-fail-undef-var.err.exp
@@ -0,0 +1,7 @@
+error: undefined variable 'y'
+
+       at «stdin»:1:4:
+
+            1| x: y
+             |    ^
+            2|
diff --git a/tests/lang/parse-fail-utf8.err.exp b/tests/lang/parse-fail-utf8.err.exp
new file mode 100644
index 000000000..6087479a3
--- /dev/null
+++ b/tests/lang/parse-fail-utf8.err.exp
@@ -0,0 +1,6 @@
+error: syntax error, unexpected invalid token, expecting end of file
+
+       at «stdin»:1:5:
+
+            1| 123 Ã
+             |     ^
diff --git a/tests/lang/parse-okay-1.exp b/tests/lang/parse-okay-1.exp
new file mode 100644
index 000000000..d5ab5f18a
--- /dev/null
+++ b/tests/lang/parse-okay-1.exp
@@ -0,0 +1 @@
+({ x, y, z }: ((x + y) + z))
diff --git a/tests/lang/parse-okay-crlf.exp b/tests/lang/parse-okay-crlf.exp
new file mode 100644
index 000000000..4213609fc
--- /dev/null
+++ b/tests/lang/parse-okay-crlf.exp
@@ -0,0 +1 @@
+rec { foo = "multi\nline\n  string\n  test\r"; x = y; y = 123; z = 456; }
diff --git a/tests/lang/parse-okay-dup-attrs-5.exp b/tests/lang/parse-okay-dup-attrs-5.exp
new file mode 100644
index 000000000..88b0b036f
--- /dev/null
+++ b/tests/lang/parse-okay-dup-attrs-5.exp
@@ -0,0 +1 @@
+{ services = { ssh = { enable = true; port = 23; }; }; }
diff --git a/tests/lang/parse-okay-dup-attrs-6.exp b/tests/lang/parse-okay-dup-attrs-6.exp
new file mode 100644
index 000000000..88b0b036f
--- /dev/null
+++ b/tests/lang/parse-okay-dup-attrs-6.exp
@@ -0,0 +1 @@
+{ services = { ssh = { enable = true; port = 23; }; }; }
diff --git a/tests/lang/parse-okay-mixed-nested-attrs-1.exp b/tests/lang/parse-okay-mixed-nested-attrs-1.exp
new file mode 100644
index 000000000..89c66f760
--- /dev/null
+++ b/tests/lang/parse-okay-mixed-nested-attrs-1.exp
@@ -0,0 +1 @@
+{ x = { q = 3; y = 3; z = 3; }; }
diff --git a/tests/lang/parse-okay-mixed-nested-attrs-2.exp b/tests/lang/parse-okay-mixed-nested-attrs-2.exp
new file mode 100644
index 000000000..89c66f760
--- /dev/null
+++ b/tests/lang/parse-okay-mixed-nested-attrs-2.exp
@@ -0,0 +1 @@
+{ x = { q = 3; y = 3; z = 3; }; }
diff --git a/tests/lang/parse-okay-mixed-nested-attrs-3.exp b/tests/lang/parse-okay-mixed-nested-attrs-3.exp
new file mode 100644
index 000000000..b89a59734
--- /dev/null
+++ b/tests/lang/parse-okay-mixed-nested-attrs-3.exp
@@ -0,0 +1 @@
+{ services = { httpd = { enable = true; }; ssh = { enable = true; port = 123; }; }; }
diff --git a/tests/lang/parse-okay-regression-20041027.exp b/tests/lang/parse-okay-regression-20041027.exp
new file mode 100644
index 000000000..9df7219e4
--- /dev/null
+++ b/tests/lang/parse-okay-regression-20041027.exp
@@ -0,0 +1 @@
+({ fetchurl, stdenv }: ((stdenv).mkDerivation { name = "libXi-6.0.1"; src = (fetchurl { md5 = "7e935a42428d63a387b3c048be0f2756"; url = "http://freedesktop.org/~xlibs/release/libXi-6.0.1.tar.bz2"; }); }))
diff --git a/tests/lang/parse-okay-regression-751.exp b/tests/lang/parse-okay-regression-751.exp
new file mode 100644
index 000000000..e2ed886fe
--- /dev/null
+++ b/tests/lang/parse-okay-regression-751.exp
@@ -0,0 +1 @@
+(let const = (a: "const"); in ((const { x = "q"; })))
diff --git a/tests/lang/parse-okay-subversion.exp b/tests/lang/parse-okay-subversion.exp
new file mode 100644
index 000000000..4168ee8bf
--- /dev/null
+++ b/tests/lang/parse-okay-subversion.exp
@@ -0,0 +1 @@
+({ fetchurl, localServer ? false, httpServer ? false, sslSupport ? false, pythonBindings ? false, javaSwigBindings ? false, javahlBindings ? false, stdenv, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null, j2sdk ? null }: assert (expat != null); assert (localServer -> (db4 != null)); assert (httpServer -> ((httpd != null) && ((httpd).expat == expat))); assert (sslSupport -> ((openssl != null) && (httpServer -> ((httpd).openssl == openssl)))); assert (pythonBindings -> ((swig != null) && (swig).pythonSupport)); assert (javaSwigBindings -> ((swig != null) && (swig).javaSupport)); assert (javahlBindings -> (j2sdk != null)); ((stdenv).mkDerivation { builder = /foo/bar; db4 = (if localServer then db4 else null); inherit expat ; inherit httpServer ; httpd = (if httpServer then httpd else null); j2sdk = (if javaSwigBindings then (swig).j2sdk else (if javahlBindings then j2sdk else null)); inherit javaSwigBindings ; inherit javahlBindings ; inherit localServer ; name = "subversion-1.1.1"; openssl = (if sslSupport then openssl else null); patches = (if javahlBindings then [ (/javahl.patch) ] else [ ]); python = (if pythonBindings then (swig).python else null); inherit pythonBindings ; src = (fetchurl { md5 = "a180c3fe91680389c210c99def54d9e0"; url = "http://subversion.tigris.org/tarballs/subversion-1.1.1.tar.bz2"; }); inherit sslSupport ; swig = (if (pythonBindings || javaSwigBindings) then swig else null); }))
diff --git a/tests/lang/parse-okay-url.exp b/tests/lang/parse-okay-url.exp
new file mode 100644
index 000000000..e5f0829b0
--- /dev/null
+++ b/tests/lang/parse-okay-url.exp
@@ -0,0 +1 @@
+[ ("x:x") ("https://svn.cs.uu.nl:12443/repos/trace/trunk") ("http://www2.mplayerhq.hu/MPlayer/releases/fonts/font-arial-iso-8859-1.tar.bz2") ("http://losser.st-lab.cs.uu.nl/~armijn/.nix/gcc-3.3.4-static-nix.tar.gz") ("http://fpdownload.macromedia.com/get/shockwave/flash/english/linux/7.0r25/install_flash_player_7_linux.tar.gz") ("https://ftp5.gwdg.de/pub/linux/archlinux/extra/os/x86_64/unzip-6.0-14-x86_64.pkg.tar.zst") ("ftp://ftp.gtk.org/pub/gtk/v1.2/gtk+-1.2.10.tar.gz") ]
diff --git a/tests/local.mk b/tests/local.mk
index 88848926b..bb80c5317 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -20,6 +20,7 @@ nix_tests = \
   remote-store.sh \
   legacy-ssh-store.sh \
   lang.sh \
+  lang-test-infra.sh \
   experimental-features.sh \
   fetchMercurial.sh \
   gc-auto.sh \
diff --git a/tests/misc.sh b/tests/misc.sh
index 60d58310e..af96d20bd 100644
--- a/tests/misc.sh
+++ b/tests/misc.sh
@@ -24,3 +24,9 @@ eval_stdin_res=$(echo 'let a = {} // a; in a.foo' | nix-instantiate --eval -E -
 echo $eval_stdin_res | grep "at «stdin»:1:15:"
 echo $eval_stdin_res | grep "infinite recursion encountered"
 
+# Attribute path errors
+expectStderr 1 nix-instantiate --eval -E '{}' -A '"x' | grepQuiet "missing closing quote in selection path"
+expectStderr 1 nix-instantiate --eval -E '[]' -A 'x' | grepQuiet "should be a set"
+expectStderr 1 nix-instantiate --eval -E '{}' -A '1' | grepQuiet "should be a list"
+expectStderr 1 nix-instantiate --eval -E '{}' -A '.' | grepQuiet "empty attribute name"
+expectStderr 1 nix-instantiate --eval -E '[]' -A '1' | grepQuiet "out of range"
diff --git a/tests/restricted.sh b/tests/restricted.sh
index 776893a56..17f310a4b 100644
--- a/tests/restricted.sh
+++ b/tests/restricted.sh
@@ -49,3 +49,5 @@ output="$(nix eval --raw --restrict-eval -I "$traverseDir" \
     2>&1 || :)"
 echo "$output" | grep "is forbidden"
 echo "$output" | grepInverse -F restricted-secret
+
+expectStderr 1 nix-instantiate --restrict-eval true ./dependencies.nix | grepQuiet "forbidden in restricted mode"

From e072e18475bc461e522f34d63cc74fc5fbf1640e Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Thu, 13 Jul 2023 08:03:42 -0400
Subject: [PATCH 3/3] Fix race condition in the language tests

When we pipe to `>(...)` like that, we unfortunately don't wait for the
process to finish. Better to just substitute the file.

Also, use the "unified" diff output that people (including myself) are
more familiar with, thanks to Git.
---
 tests/lang.sh           | 5 +++--
 tests/lang/framework.sh | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/tests/lang.sh b/tests/lang.sh
index bfb942d3d..75dbbc38e 100755
--- a/tests/lang.sh
+++ b/tests/lang.sh
@@ -52,9 +52,10 @@ for i in lang/parse-okay-*.nix; do
     i=$(basename "$i" .nix)
     if
         expect 0 nix-instantiate --parse - < "lang/$i.nix" \
-            1> >(sed "s!$(pwd)!/pwd!g" > "lang/$i.out") \
-            2> >(sed "s!$(pwd)!/pwd!g" > "lang/$i.err")
+            1> "lang/$i.out" \
+            2> "lang/$i.err"
     then
+        sed "s!$(pwd)!/pwd!g" "lang/$i.out" "lang/$i.err"
         diffAndAccept "$i" out exp
         diffAndAccept "$i" err err.exp
     else
diff --git a/tests/lang/framework.sh b/tests/lang/framework.sh
index d6499e0e9..516bff8ad 100644
--- a/tests/lang/framework.sh
+++ b/tests/lang/framework.sh
@@ -16,7 +16,7 @@ function diffAndAcceptInner() {
     fi
 
     # Diff so we get a nice message
-    if ! diff "$got" "$expectedOrEmpty"; then
+    if ! diff --unified "$got" "$expectedOrEmpty"; then
         echo "FAIL: evaluation result of $testName not as expected"
         badDiff=1
     fi