make cfg parser suggest any or all on #[cfg(a, b)]

Author: scrabsha

compiler/rustc_attr_parsing/src/attributes/cfg.rs

@@ -48,8 +48,37 @@ pub fn parse_cfg<S: Stage>(
         cx.adcx().expected_list(attr_span, args);
         return None;
     };
+
     let Some(single) = list.single() else {
-        cx.adcx().expected_single_argument(list.span);
+        let target = cx.target;
+        let mut adcx = cx.adcx();
+        if list.is_empty() {
+            // `#[cfg()]`
+            let message = format!("if {target} should be disabled, use `#[cfg(false)]`");
+            adcx.push_suggestion(message, list.span, "(false)".to_string());
+        } else {
+            // `#[cfg(foo, bar)]`
+            if let Ok(args) = adcx
+                .sess()
+                .source_map()
+                .span_to_source(list.span, |src, start, end| Ok(src[start..end].to_string()))
+            {
+                let all = format!("(all{args})");
+                let any = format!("(any{args})");
+
+                let all_msg = format!(
+                    "if the {target} should be enabled when all these predicates are, wrap them in `all`"
+                );
+                let any_msg = format!(
+                    "alternately, if the {target} should be enabled when any these predicates are, wrap them in `any`"
+                );
+
+                adcx.push_suggestion(all_msg, list.span, all);
+                adcx.push_suggestion(any_msg, list.span, any);
+            }
+        }
+
+        adcx.expected_single_argument(list.span);
         return None;
     };
     parse_cfg_entry(cx, single).ok()

tests/ui/cfg/suggest-any-or-all.stderr

@@ -3,11 +3,20 @@ error[E0805]: malformed `cfg` attribute input
    |
 LL | #[cfg(foo, bar)]
    | ^^^^^----------^
-   | |    |
-   | |    expected a single argument here
-   | help: must be of the form: `#[cfg(predicate)]`
+   |      |
+   |      expected a single argument here
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
+help: if the crate should be enabled when all these predicates are, wrap them in `all`
+   |
+LL - #[cfg(foo, bar)]
+LL + #[cfg(all(foo, bar))]
+   |
+help: alternately, if the crate should be enabled when any these predicates are, wrap them in `any`
+   |
+LL - #[cfg(foo, bar)]
+LL + #[cfg(any(foo, bar))]
+   |
 
 error: aborting due to 1 previous error
 

tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr

@@ -25,22 +25,34 @@ error[E0805]: malformed `cfg` attribute input
    |
 LL | #[cfg()]
    | ^^^^^--^
-   | |    |
-   | |    expected a single argument here
-   | help: must be of the form: `#[cfg(predicate)]`
+   |      |
+   |      expected a single argument here
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
+help: if crate should be disabled, use `#[cfg(false)]`
+   |
+LL | #[cfg(false)]
+   |       +++++
 
 error[E0805]: malformed `cfg` attribute input
   --> $DIR/cfg-attr-syntax-validation.rs:19:1
    |
 LL | #[cfg(a, b)]
    | ^^^^^------^
-   | |    |
-   | |    expected a single argument here
-   | help: must be of the form: `#[cfg(predicate)]`
+   |      |
+   |      expected a single argument here
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
+help: if the crate should be enabled when all these predicates are, wrap them in `all`
+   |
+LL - #[cfg(a, b)]
+LL + #[cfg(all(a, b))]
+   |
+help: alternately, if the crate should be enabled when any these predicates are, wrap them in `any`
+   |
+LL - #[cfg(a, b)]
+LL + #[cfg(any(a, b))]
+   |
 
 error[E0539]: malformed `cfg` attribute input
   --> $DIR/cfg-attr-syntax-validation.rs:25:1