Fix a case where completion was unable to expand a macro

Which caused the macros of the popular `tracing` crate to not offer completions.

The reason is rather complicated: it boils down to macro ignoring their input and completion always choosing the first expansion.

crates/hir-expand/src/db.rs

@@ -153,13 +153,13 @@ fn syntax_context(db: &dyn ExpandDatabase, file: HirFileId) -> SyntaxContextId {
 /// This expands the given macro call, but with different arguments. This is
 /// used for completion, where we want to see what 'would happen' if we insert a
 /// token. The `token_to_map` mapped down into the expansion, with the mapped
-/// token returned.
+/// token(s) returned with their priority.
 pub fn expand_speculative(
     db: &dyn ExpandDatabase,
     actual_macro_call: MacroCallId,
     speculative_args: &SyntaxNode,
     token_to_map: SyntaxToken,
-) -> Option<(SyntaxNode, SyntaxToken)> {
+) -> Option<(SyntaxNode, Vec<(SyntaxToken, u8)>)> {
     let loc = db.lookup_intern_macro_call(actual_macro_call);
     let (_, _, span) = db.macro_arg_considering_derives(actual_macro_call, &loc.kind);
 
@@ -303,17 +303,19 @@ pub fn expand_speculative(
         token_tree_to_syntax_node(&speculative_expansion.value, expand_to, loc.def.edition);
 
     let syntax_node = node.syntax_node();
-    let (token, _) = rev_tmap
+    let token = rev_tmap
         .ranges_with_span(span_map.span_for_range(token_to_map.text_range()))
         .filter_map(|(range, ctx)| syntax_node.covering_element(range).into_token().zip(Some(ctx)))
-        .min_by_key(|(t, ctx)| {
+        .map(|(t, ctx)| {
             // prefer tokens of the same kind and text, as well as non opaque marked ones
             // Note the inversion of the score here, as we want to prefer the first token in case
             // of all tokens having the same score
-            ctx.is_opaque(db) as u8
+            let ranking = ctx.is_opaque(db) as u8
                 + 2 * (t.kind() != token_to_map.kind()) as u8
-                + 4 * ((t.text() != token_to_map.text()) as u8)
-        })?;
+                + 4 * ((t.text() != token_to_map.text()) as u8);
+            (t, ranking)
+        })
+        .collect();
     Some((node.syntax_node(), token))
 }
 

crates/hir/src/semantics.rs

@@ -571,7 +571,7 @@ impl<'db> SemanticsImpl<'db> {
         actual_macro_call: &ast::MacroCall,
         speculative_args: &ast::TokenTree,
         token_to_map: SyntaxToken,
-    ) -> Option<(SyntaxNode, SyntaxToken)> {
+    ) -> Option<(SyntaxNode, Vec<(SyntaxToken, u8)>)> {
         let SourceAnalyzer { file_id, resolver, .. } =
             self.analyze_no_infer(actual_macro_call.syntax())?;
         let macro_call = InFile::new(file_id, actual_macro_call);
@@ -592,7 +592,7 @@ impl<'db> SemanticsImpl<'db> {
         macro_file: MacroFileId,
         speculative_args: &SyntaxNode,
         token_to_map: SyntaxToken,
-    ) -> Option<(SyntaxNode, SyntaxToken)> {
+    ) -> Option<(SyntaxNode, Vec<(SyntaxToken, u8)>)> {
         hir_expand::db::expand_speculative(
             self.db.upcast(),
             macro_file.macro_call_id,
@@ -608,7 +608,7 @@ impl<'db> SemanticsImpl<'db> {
         actual_macro_call: &ast::Item,
         speculative_args: &ast::Item,
         token_to_map: SyntaxToken,
-    ) -> Option<(SyntaxNode, SyntaxToken)> {
+    ) -> Option<(SyntaxNode, Vec<(SyntaxToken, u8)>)> {
         let macro_call = self.wrap_node_infile(actual_macro_call.clone());
         let macro_call_id = self.with_ctx(|ctx| ctx.item_to_macro_call(macro_call.as_ref()))?;
         hir_expand::db::expand_speculative(
@@ -624,7 +624,7 @@ impl<'db> SemanticsImpl<'db> {
         actual_macro_call: &ast::Attr,
         speculative_args: &ast::Attr,
         token_to_map: SyntaxToken,
-    ) -> Option<(SyntaxNode, SyntaxToken)> {
+    ) -> Option<(SyntaxNode, Vec<(SyntaxToken, u8)>)> {
         let attr = self.wrap_node_infile(actual_macro_call.clone());
         let adt = actual_macro_call.syntax().parent().and_then(ast::Adt::cast)?;
         let macro_call_id = self.with_ctx(|ctx| {

crates/ide-completion/src/context.rs

@@ -718,7 +718,7 @@ impl<'a> CompletionContext<'a> {
             expected: (expected_type, expected_name),
             qualifier_ctx,
             token,
-            offset,
+            original_offset,
         } = expand_and_analyze(
             &sema,
             original_file.syntax().clone(),
@@ -728,7 +728,7 @@ impl<'a> CompletionContext<'a> {
         )?;
 
         // adjust for macro input, this still fails if there is no token written yet
-        let scope = sema.scope_at_offset(&token.parent()?, offset)?;
+        let scope = sema.scope_at_offset(&token.parent()?, original_offset)?;
 
         let krate = scope.krate();
         let module = scope.module();