From a34ac6f13a5d5b45433e57a436ca0e80dd395447 Mon Sep 17 00:00:00 2001
From: Urgau <urgau@numericable.fr>
Date: Wed, 17 Jan 2024 19:12:53 +0100
Subject: [PATCH] Go back to passing an empty values() when no features are
 declared

See https://github.com/rust-lang/rust/pull/119930
---
 src/cargo/core/compiler/mod.rs | 31 ++++++++++++-------------------
 tests/testsuite/check_cfg.rs   | 14 +++++++-------
 2 files changed, 19 insertions(+), 26 deletions(-)

diff --git a/src/cargo/core/compiler/mod.rs b/src/cargo/core/compiler/mod.rs
index eefd08e09bed..5226d8bfdd17 100644
--- a/src/cargo/core/compiler/mod.rs
+++ b/src/cargo/core/compiler/mod.rs
@@ -1270,34 +1270,27 @@ fn check_cfg_args(cx: &Context<'_, '_>, unit: &Unit) -> Vec<OsString> {
         //
         // but having `cfg()` is redundant with the second argument (as well-known names
         // and values are implicitly enabled when one or more `--check-cfg` argument is
-        // passed) so we don't emit it:
+        // passed) so we don't emit it and just pass:
         //
         //   --check-cfg=cfg(feature, values(...))
         //
-        // expect when there are no features declared, where we can't generate the
-        // `cfg(feature, values())` argument since it would mean that it is somehow
-        // possible to have a `#[cfg(feature)]` without a feature name, which is
-        // impossible and not what we want, so we just generate:
-        //
-        //   --check-cfg=cfg()
+        // This way even when there are no declared features the config `feature` will
+        // still be declared, meaning users would get "unexpected value" instead of name.
+        // This wasn't always the case see rust-lang#119930 for some details.
 
         let gross_cap_estimation = unit.pkg.summary().features().len() * 7 + 25;
         let mut arg_feature = OsString::with_capacity(gross_cap_estimation);
 
-        arg_feature.push("cfg(");
-        if !unit.pkg.summary().features().is_empty() {
-            arg_feature.push("feature, values(");
-            for (i, feature) in unit.pkg.summary().features().keys().enumerate() {
-                if i != 0 {
-                    arg_feature.push(", ");
-                }
-                arg_feature.push("\"");
-                arg_feature.push(feature);
-                arg_feature.push("\"");
+        arg_feature.push("cfg(feature, values(");
+        for (i, feature) in unit.pkg.summary().features().keys().enumerate() {
+            if i != 0 {
+                arg_feature.push(", ");
             }
-            arg_feature.push(")");
+            arg_feature.push("\"");
+            arg_feature.push(feature);
+            arg_feature.push("\"");
         }
-        arg_feature.push(")");
+        arg_feature.push("))");
 
         vec![
             OsString::from("-Zunstable-options"),
diff --git a/tests/testsuite/check_cfg.rs b/tests/testsuite/check_cfg.rs
index 47d4e278dbc0..5f34774094ed 100644
--- a/tests/testsuite/check_cfg.rs
+++ b/tests/testsuite/check_cfg.rs
@@ -15,16 +15,16 @@ macro_rules! x {
                     $what, '(', $($who,)* ')', "'", "[..]")
         }
     }};
-    ($tool:tt => $what:tt of $who:tt with $first_value:tt $($other_values:tt)*) => {{
+    ($tool:tt => $what:tt of $who:tt with $($first_value:tt $($other_values:tt)*)?) => {{
         #[cfg(windows)]
         {
             concat!("[RUNNING] [..]", $tool, "[..] --check-cfg \"",
-                    $what, '(', $who, ", values(", "/\"", $first_value, "/\"", $(", ", "/\"", $other_values, "/\"",)* "))", '"', "[..]")
+                    $what, '(', $who, ", values(", $("/\"", $first_value, "/\"", $(", ", "/\"", $other_values, "/\"",)*)* "))", '"', "[..]")
         }
         #[cfg(not(windows))]
         {
             concat!("[RUNNING] [..]", $tool, "[..] --check-cfg '",
-                    $what, '(', $who, ", values(", "\"", $first_value, "\"", $(", ", "\"", $other_values, "\"",)* "))", "'", "[..]")
+                    $what, '(', $who, ", values(", $("\"", $first_value, "\"", $(", ", "\"", $other_values, "\"",)*)* "))", "'", "[..]")
         }
     }};
 }
@@ -221,7 +221,7 @@ fn well_known_names_values() {
 
     p.cargo("check -v -Zcheck-cfg")
         .masquerade_as_nightly_cargo(&["check-cfg"])
-        .with_stderr_contains(x!("rustc" => "cfg"))
+        .with_stderr_contains(x!("rustc" => "cfg" of "feature" with))
         .run();
 }
 
@@ -284,7 +284,7 @@ fn well_known_names_values_test() {
 
     p.cargo("test -v -Zcheck-cfg")
         .masquerade_as_nightly_cargo(&["check-cfg"])
-        .with_stderr_contains(x!("rustc" => "cfg"))
+        .with_stderr_contains(x!("rustc" => "cfg" of "feature" with))
         .run();
 }
 
@@ -297,8 +297,8 @@ fn well_known_names_values_doctest() {
 
     p.cargo("test -v --doc -Zcheck-cfg")
         .masquerade_as_nightly_cargo(&["check-cfg"])
-        .with_stderr_contains(x!("rustc" => "cfg"))
-        .with_stderr_contains(x!("rustdoc" => "cfg"))
+        .with_stderr_contains(x!("rustc" => "cfg" of "feature" with))
+        .with_stderr_contains(x!("rustdoc" => "cfg" of "feature" with))
         .run();
 }