Handle no values cfg with --print=check-cfg

Author: Urgau

compiler/rustc_driver_impl/src/lib.rs

@@ -814,13 +814,17 @@ fn print_crate_info(
                     match expected_values {
                         ExpectedValues::Any => check_cfgs.push(format!("{name}=any()")),
                         ExpectedValues::Some(values) => {
-                            check_cfgs.extend(values.iter().map(|value| {
-                                if let Some(value) = value {
-                                    format!("{name}=\"{value}\"")
-                                } else {
-                                    name.to_string()
-                                }
-                            }))
+                            if !values.is_empty() {
+                                check_cfgs.extend(values.iter().map(|value| {
+                                    if let Some(value) = value {
+                                        format!("{name}=\"{value}\"")
+                                    } else {
+                                        name.to_string()
+                                    }
+                                }))
+                            } else {
+                                check_cfgs.push(format!("{name}="))
+                            }
                         }
                     }
                 }

src/doc/unstable-book/src/compiler-flags/print-check-cfg.md

@@ -15,6 +15,7 @@ This print option works similarly to `--print=cfg` (modulo check-cfg specifics):
  - `cfg(feature, values("foo", "bar"))`: `feature="foo"` and `feature="bar"`
  - `cfg(feature, values(none(), ""))`: `feature` and `feature=""`
  - `cfg(feature, values(any()))`: `feature=any()`
+ - `cfg(feature, values())`: `feature=`
  - `cfg(any())`: `any()`
  - *nothing*: `any()=any()`
 

tests/run-make/print-check-cfg/rmake.rs

@@ -33,6 +33,21 @@ fn main() {
         /*has_any_any*/ false,
         /*contains*/ &["unix", "miri", "feature"],
     );
+    check(
+        /*args*/ &["--check-cfg=cfg(feature, values())"],
+        /*has_any*/ false,
+        /*has_any_any*/ false,
+        /*contains*/ &["feature="],
+    );
+    check(
+        /*args*/ &[
+            "--check-cfg=cfg(feature, values())",
+            "--check-cfg=cfg(feature, values(none()))"
+        ],
+        /*has_any*/ false,
+        /*has_any_any*/ false,
+        /*contains*/ &["feature"],
+    );
     check(
         /*args*/ &[r#"--check-cfg=cfg(feature, values(none(), "", "test", "lol"))"#],
         /*has_any*/ false,