Auto merge of #13316 - Urgau:check-cfg-zero-features-2, r=epage

Go back to passing an empty `values()` when no features are declared

This PR is basically a revert of #13011, which made the `--check-cfg` invocation be `cfg()` when no features are declared instead of `cfg(feature, values())` since it meant declaring that the config `feature` were to be available in this form: `#[cfg(feature)]`, which is not the case.

Thankfully after some brainstorming, I [proposed](rust-lang/rust#119930) changing the behavior of empty `values()` in `rustc` to no longer imply the _none_ value and simply create an empty set of expected values. 😃

For Cargo, always using `cfg(feature, values(...))` means that the config `feature` is always expected, regardless of the number of features. This makes the warning better, as it will now always be `unexpected config value` (instead of `unexpected config name`). 🎉

Fixes #13011 (comment) as well as the concern in the [tracking issue](#10554).

r? `@epage`

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 if there are no declared features, the config `feature` will
+        // still be expected, 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"),

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();
 }