Implicit format args support

crates/ide/src/highlight_related.rs

@@ -1,3 +1,5 @@
+use std::iter;
+
 use hir::{DescendPreference, Semantics};
 use ide_db::{
     base_db::{FileId, FilePosition, FileRange},
@@ -15,7 +17,6 @@ use syntax::{
     SyntaxKind::{self, IDENT, INT_NUMBER},
     SyntaxNode, SyntaxToken, TextRange, T,
 };
-use text_edit::TextSize;
 
 use crate::{navigation_target::ToNav, references, NavigationTarget, TryToNav};
 
@@ -132,7 +133,16 @@ fn highlight_references(
     token: SyntaxToken,
     FilePosition { file_id, offset }: FilePosition,
 ) -> Option<Vec<HighlightedRange>> {
-    let defs = find_defs(sema, token.clone(), offset);
+    let defs = if let Some((range, resolution)) =
+        sema.check_for_format_args_template(token.clone(), offset)
+    {
+        match resolution.map(Definition::from) {
+            Some(def) => iter::once(def).collect(),
+            None => return Some(vec![HighlightedRange { range, category: None }]),
+        }
+    } else {
+        find_defs(sema, token.clone())
+    };
     let usages = defs
         .iter()
         .filter_map(|&d| {
@@ -456,12 +466,8 @@ fn cover_range(r0: Option<TextRange>, r1: Option<TextRange>) -> Option<TextRange
     }
 }
 
-fn find_defs(
-    sema: &Semantics<'_, RootDatabase>,
-    token: SyntaxToken,
-    offset: TextSize,
-) -> FxHashSet<Definition> {
-    sema.descend_into_macros(DescendPreference::None, token, offset)
+fn find_defs(sema: &Semantics<'_, RootDatabase>, token: SyntaxToken) -> FxHashSet<Definition> {
+    sema.descend_into_macros(DescendPreference::None, token)
         .into_iter()
         .filter_map(|token| IdentClass::classify_token(sema, &token))
         .map(IdentClass::definitions_no_ops)
@@ -1620,6 +1626,23 @@ fn f2<T: Foo>(t: T) {
     T::C;
     T::f();
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn implicit_format_args() {
+        check(
+            r#"
+//- minicore: fmt
+fn test() {
+    let a = "foo";
+     // ^
+    format_args!("hello {a} {a$0} {}", a);
+                      // ^read
+                          // ^read
+                                  // ^read
+}
 "#,
         );
     }