Fix suggestion for the cfg! macro

Signed-off-by: Jonathan Brouwer <jonathantbrouwer@gmail.com>

compiler/rustc_attr_parsing/src/attributes/cfg.rs

@@ -2,7 +2,7 @@
 use rustc_ast::tokenstream::DelimSpan;
 use rustc_ast::{AttrItem, Attribute, CRATE_NODE_ID, LitKind, NodeId, ast, token};
 use rustc_errors::{Applicability, PResult};
-use rustc_feature::{AttributeTemplate, Features, template};
+use rustc_feature::{AttrSuggestionStyle, AttributeTemplate, Features, template};
 use rustc_hir::attrs::CfgEntry;
 use rustc_hir::{AttrPath, RustcVersion};
 use rustc_parse::parser::{ForceCollect, Parser};
@@ -324,8 +324,8 @@ pub fn parse_cfg_attr(
             }) {
                 Ok(r) => return Some(r),
                 Err(e) => {
-                    let suggestions =
-                        CFG_ATTR_TEMPLATE.suggestions(Some(cfg_attr.style), sym::cfg_attr);
+                    let suggestions = CFG_ATTR_TEMPLATE
+                        .suggestions(AttrSuggestionStyle::Attribute(cfg_attr.style), sym::cfg_attr);
                     e.with_span_suggestions(
                         cfg_attr.span,
                         "must be of the form",
@@ -356,7 +356,8 @@ pub fn parse_cfg_attr(
                 path: AttrPath::from_ast(&cfg_attr.get_normal_item().path),
                 description: ParsedDescription::Attribute,
                 reason,
-                suggestions: CFG_ATTR_TEMPLATE.suggestions(Some(cfg_attr.style), sym::cfg_attr),
+                suggestions: CFG_ATTR_TEMPLATE
+                    .suggestions(AttrSuggestionStyle::Attribute(cfg_attr.style), sym::cfg_attr),
             });
         }
     }

compiler/rustc_attr_parsing/src/context.rs

@@ -6,7 +6,7 @@
 use private::Sealed;
 use rustc_ast::{AttrStyle, CRATE_NODE_ID, MetaItemLit, NodeId};
 use rustc_errors::{Diag, Diagnostic, Level};
-use rustc_feature::AttributeTemplate;
+use rustc_feature::{AttrSuggestionStyle, AttributeTemplate};
 use rustc_hir::attrs::AttributeKind;
 use rustc_hir::lints::{AttributeLint, AttributeLintKind};
 use rustc_hir::{AttrPath, CRATE_HIR_ID, HirId};
@@ -638,9 +638,15 @@ pub(crate) fn warn_empty_attribute(&mut self, span: Span) {
     }
 
     pub(crate) fn suggestions(&self) -> Vec<String> {
-        // If the outer and inner spans are equal, we are parsing an attribute from `cfg_attr`,
-        // So don't display an attribute style in the suggestions
-        let style = (self.attr_span != self.inner_span).then_some(self.attr_style);
+        let style = match self.parsed_description {
+            // If the outer and inner spans are equal, we are parsing an embedded attribute
+            ParsedDescription::Attribute if self.attr_span == self.inner_span => {
+                AttrSuggestionStyle::EmbeddedAttribute
+            }
+            ParsedDescription::Attribute => AttrSuggestionStyle::Attribute(self.attr_style),
+            ParsedDescription::Macro => AttrSuggestionStyle::Macro,
+        };
+
         self.template.suggestions(style, &self.attr_path)
     }
 }

compiler/rustc_feature/src/builtin_attrs.rs

@@ -132,28 +132,45 @@ pub struct AttributeTemplate {
     pub docs: Option<&'static str>,
 }
 
+pub enum AttrSuggestionStyle {
+    /// The suggestion is styled for a normal attribute.
+    /// The `AttrStyle` determines whether this is an inner or outer attribute.
+    Attribute(AttrStyle),
+    /// The suggestion is styled for an attribute embedded into another attribute.
+    /// For example, attributes inside `#[cfg_attr(true, attr(...)]`.
+    EmbeddedAttribute,
+    /// The suggestion is styled for macros that are parsed with attribute parsers.
+    /// For example, the `cfg!(predicate)` macro.
+    Macro,
+}
+
 impl AttributeTemplate {
     pub fn suggestions(
         &self,
-        style: Option<AttrStyle>,
+        style: AttrSuggestionStyle,
         name: impl std::fmt::Display,
     ) -> Vec<String> {
-        let mut suggestions = vec![];
-        let (start, end) = match style {
-            Some(AttrStyle::Outer) => ("#[", "]"),
-            Some(AttrStyle::Inner) => ("#![", "]"),
-            None => ("", ""),
+        let (start, macro_call, end) = match style {
+            AttrSuggestionStyle::Attribute(AttrStyle::Outer) => ("#[", "", "]"),
+            AttrSuggestionStyle::Attribute(AttrStyle::Inner) => ("#![", "", "]"),
+            AttrSuggestionStyle::Macro => ("", "!", ""),
+            AttrSuggestionStyle::EmbeddedAttribute => ("", "", ""),
         };
+
+        let mut suggestions = vec![];
+
         if self.word {
+            debug_assert!(macro_call.is_empty(), "Macro suggestions use list style");
             suggestions.push(format!("{start}{name}{end}"));
         }
         if let Some(descr) = self.list {
             for descr in descr {
-                suggestions.push(format!("{start}{name}({descr}){end}"));
+                suggestions.push(format!("{start}{name}{macro_call}({descr}){end}"));
             }
         }
         suggestions.extend(self.one_of.iter().map(|&word| format!("{start}{name}({word}){end}")));
         if let Some(descr) = self.name_value_str {
+            debug_assert!(macro_call.is_empty(), "Macro suggestions use list style");
             for descr in descr {
                 suggestions.push(format!("{start}{name} = \"{descr}\"{end}"));
             }

compiler/rustc_feature/src/lib.rs

@@ -135,9 +135,10 @@ pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZero<u
 
 pub use accepted::ACCEPTED_LANG_FEATURES;
 pub use builtin_attrs::{
-    AttributeDuplicates, AttributeGate, AttributeSafety, AttributeTemplate, AttributeType,
-    BUILTIN_ATTRIBUTE_MAP, BUILTIN_ATTRIBUTES, BuiltinAttribute, GatedCfg, encode_cross_crate,
-    find_gated_cfg, is_builtin_attr_name, is_stable_diagnostic_attribute, is_valid_for_get_attr,
+    AttrSuggestionStyle, AttributeDuplicates, AttributeGate, AttributeSafety, AttributeTemplate,
+    AttributeType, BUILTIN_ATTRIBUTE_MAP, BUILTIN_ATTRIBUTES, BuiltinAttribute, GatedCfg,
+    encode_cross_crate, find_gated_cfg, is_builtin_attr_name, is_stable_diagnostic_attribute,
+    is_valid_for_get_attr,
 };
 pub use removed::REMOVED_LANG_FEATURES;
 pub use unstable::{

tests/ui/macros/cfg.stderr

@@ -11,7 +11,7 @@ LL |     cfg!(123);
    |     ^^^^^---^
    |     |    |
    |     |    expected a valid identifier here
-   |     help: must be of the form: `cfg(predicate)`
+   |     help: must be of the form: `cfg!(predicate)`
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
 
@@ -22,7 +22,7 @@ LL |     cfg!(foo = 123);
    |     ^^^^^^^^^^^---^
    |     |          |
    |     |          expected a string literal here
-   |     help: must be of the form: `cfg(predicate)`
+   |     help: must be of the form: `cfg!(predicate)`
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
 

tests/ui/span/E0805.stderr

@@ -5,7 +5,7 @@ LL |     if cfg!(not()) { }
    |        ^^^^^^^^--^
    |        |       |
    |        |       expected a single argument here
-   |        help: must be of the form: `cfg(predicate)`
+   |        help: must be of the form: `cfg!(predicate)`
    |
    = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>