From f6078e474d5fc41c8a7f683865d60490bf0c7040 Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Tue, 8 Mar 2022 16:20:01 +0100
Subject: [PATCH] Also display some suggestions for invalid formal arguments
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```console
$ nix eval --expr '({ foo ? 1 }: foo) { fob = 2; }'
error: anonymous function at (string):1:2 called with unexpected argument 'fob'

       at «string»:1:1:

            1| ({ foo ? 1 }: foo) { fob = 2; }
             | ^
       Did you mean foo?
```

Not that because Nix will first check for _missing_ arguments before
checking for extra arguments, `({ foo }: foo) { fob = 1; }` will
complain about the missing `foo` argument (rather than extra `fob`) and
so won’t display a suggestion.
---
 src/libexpr/eval.cc  | 23 +++++++++++++++++++++--
 tests/suggestions.sh |  4 ++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 3bfb82b16..a5e9dc286 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -782,6 +782,16 @@ LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const char * s, const
     });
 }
 
+LocalNoInlineNoReturn(void throwTypeError(const Pos & pos, const Suggestions & suggestions, const char * s, const ExprLambda & fun, const Symbol & s2))
+{
+    throw TypeError(ErrorInfo {
+        .msg = hintfmt(s, fun.showNamePos(), s2),
+        .errPos = pos,
+        .suggestions = suggestions,
+    });
+}
+
+
 LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v))
 {
     throw TypeError(s, showType(v));
@@ -1414,8 +1424,17 @@ void EvalState::callFunction(Value & fun, size_t nrArgs, Value * * args, Value &
                     /* Nope, so show the first unexpected argument to the
                        user. */
                     for (auto & i : *args[0]->attrs)
-                        if (!lambda.formals->has(i.name))
-                            throwTypeError(pos, "%1% called with unexpected argument '%2%'", lambda, i.name);
+                        if (!lambda.formals->has(i.name)) {
+                            std::set<std::string> formalNames;
+                            for (auto & formal : lambda.formals->formals)
+                                formalNames.insert(formal.name);
+                            throwTypeError(
+                                pos,
+                                Suggestions::bestMatches(formalNames, i.name),
+                                "%1% called with unexpected argument '%2%'",
+                                lambda,
+                                i.name);
+                        }
                     abort(); // can't happen
                 }
             }
diff --git a/tests/suggestions.sh b/tests/suggestions.sh
index 29d5b364b..f18fefef9 100644
--- a/tests/suggestions.sh
+++ b/tests/suggestions.sh
@@ -38,3 +38,7 @@ NIX_BUILD_STDERR_WITH_NO_CLOSE_SUGGESTION=$(! nix build .\#bar 2>&1 1>/dev/null)
 NIX_EVAL_STDERR_WITH_SUGGESTIONS=$(! nix build --impure --expr '(builtins.getFlake (builtins.toPath ./.)).packages.'$system'.fob' 2>&1 1>/dev/null)
 [[ "$NIX_EVAL_STDERR_WITH_SUGGESTIONS" =~ "Did you mean one of fo1, fo2, foo or fooo?" ]] || \
     fail "The evaluator should suggest the three closest possiblities"
+
+NIX_EVAL_STDERR_WITH_SUGGESTIONS=$(! nix build --impure --expr '({ foo }: foo) { foo = 1; fob = 2; }' 2>&1 1>/dev/null)
+[[ "$NIX_EVAL_STDERR_WITH_SUGGESTIONS" =~ "Did you mean foo?" ]] || \
+    fail "The evaluator should suggest the three closest possiblities"