libexpr: Deprecate URL literals

Closes #437.

Change-Id: I9f67fc965bb4a7e7fd849e5067ac1cb3bab064cd

doc/manual/rl-next/deprecated-features.md

@@ -0,0 +1,12 @@
+---
+synopsis: Deprecated URL literals
+issues: [fj#437]
+cls: [1736, 1735, 1744]
+category: Breaking Changes
+credits: [piegames, horrors]
+---
+
+URL literals have long been obsolete and discouraged of use, and now they are officially deprecated.
+This means that all URLs must be properly put within quotes like all other strings.
+
+To ease migration, they can still be enabled with `--extra-deprecated-features url-literals` for now.

doc/manual/src/language/values.md

@@ -77,12 +77,6 @@
   }
   ```
 
-  Finally, as a convenience, *URIs* as defined in appendix B of
-  [RFC 2396](http://www.ietf.org/rfc/rfc2396.txt) can be written *as
-  is*, without quotes. For instance, the string
-  `"http://example.org/foo.tar.bz2"` can also be written as
-  `http://example.org/foo.tar.bz2`.
-
 - <a id="type-number" href="#type-number">Number</a>
 
   Numbers, which can be *integers* (like `123`) or *floating point*

src/libexpr/parser/parser.cc

@@ -656,10 +656,10 @@ template<> struct BuildAST<grammar::expr::path> : p::maybe_nothing {};
 
 template<> struct BuildAST<grammar::expr::uri> {
     static void apply(const auto & in, ExprState & s, State & ps) {
-       bool noURLLiterals = ps.featureSettings.isEnabled(Xp::NoUrlLiterals);
+       bool URLLiterals = ps.featureSettings.isEnabled(Dep::UrlLiterals);
-       if (noURLLiterals)
+       if (!URLLiterals)
            throw ParseError({
-               .msg = HintFmt("URL literals are disabled"),
+               .msg = HintFmt("URL literals are deprecated, allow using them with --extra-deprecated-features=url-literals"),
                .pos = ps.positions[ps.at(in)]
            });
        s.pushExpr<ExprString>(ps.at(in), in.string());

src/libutil/config.hh

@@ -488,7 +488,13 @@ struct FeatureSettings : Config {
     Setting<std::set<DeprecatedFeature>> deprecatedFeatures{
         this, {}, "deprecated-features",
         R"(
-          Deprecated features that are allowed. (Currently there are none.)
+          Deprecated features that are allowed.
+
+          Example:
+
+          ```
+          deprecated-features = url-literals
+          ```
 
           The following deprecated feature features can be re-activated:
 

src/libutil/deprecated-features.cc

@@ -24,9 +24,16 @@ struct DeprecatedFeatureDetails
  * feature, we either have no issue at all if few features are not added
  * at the end of the list, or a proper merge conflict if they are.
  */
-constexpr size_t numDepFeatures = 0;
+constexpr size_t numDepFeatures = 1 + static_cast<size_t>(Dep::UrlLiterals);
 
 constexpr std::array<DeprecatedFeatureDetails, numDepFeatures> depFeatureDetails = {{
+    {
+        .tag = Dep::UrlLiterals,
+        .name = "url-literals",
+        .description = R"(
+            Allow unquoted URLs as part of the Nix language syntax.
+        )",
+    },
 }};
 
 static_assert(

src/libutil/deprecated-features.hh

@@ -18,6 +18,7 @@ namespace nix {
  */
 enum struct DeprecatedFeature
 {
+    UrlLiterals
 };
 
 /**

tests/functional/lang.sh

@@ -53,8 +53,13 @@ done
 for i in lang/parse-okay-*.nix; do
     echo "parsing $i (should succeed)";
     i=$(basename "$i" .nix)
+    # Hard-code that these two files are allowed to use url literals (because they test them)
+    if [[ "$i" == "parse-okay-url" || "$i" == "parse-okay-regression-20041027" ]]
+    then
+        extraArgs="--extra-deprecated-features url-literals"
+    fi
     if
-        expect 0 nix-instantiate --parse - < "lang/$i.nix" \
+        expect 0 nix-instantiate --parse ${extraArgs-} - < "lang/$i.nix" \
             1> "lang/$i.out" \
             2> "lang/$i.err"
     then

tests/functional/lang/parse-okay-regression-20041027.nix

@@ -1,3 +1,4 @@
+# This test needs to be run with --extra-deprecated-features url-literals
 {stdenv, fetchurl /* pkgconfig, libX11 */ }:
 
 stdenv.mkDerivation {

tests/functional/lang/parse-okay-url.nix

@@ -1,3 +1,4 @@
+# This test needs to be run with --extra-deprecated-features url-literals
 [ 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

tests/unit/libexpr/trivial.cc

@@ -87,15 +87,15 @@ namespace nix {
     }
 
     TEST_F(TrivialExpressionTest, urlLiteral) {
-        auto v = eval("https://nixos.org");
+        FeatureSettings mockFeatureSettings;
+        mockFeatureSettings.set("deprecated-features", "url-literals");
+
+        auto v = eval("https://nixos.org", true, mockFeatureSettings);
         ASSERT_THAT(v, IsStringEq("https://nixos.org"));
     }
 
     TEST_F(TrivialExpressionTest, noUrlLiteral) {
-        ExperimentalFeatureSettings mockXpSettings;
+        ASSERT_THROW(eval("https://nixos.org"), Error);
-        mockXpSettings.set("experimental-features", "no-url-literals");
-
-        ASSERT_THROW(eval("https://nixos.org", true, mockXpSettings), Error);
     }
 
     TEST_F(TrivialExpressionTest, withFound) {