Merge #11714

11714: fix: Fix completions not always working in for-loop patterns r=Veykril a=Veykril

Fixes https://github.com/rust-analyzer/rust-analyzer/issues/11205
bors r+

Co-authored-by: Lukas Wirth <lukastw97@gmail.com>

crates/ide_completion/src/context.rs

@@ -24,8 +24,8 @@ use text_edit::Indel;
 
 use crate::{
     patterns::{
-        determine_location, determine_prev_sibling, for_is_prev2, is_in_loop_body, previous_token,
-        ImmediateLocation, ImmediatePrevSibling,
+        determine_location, determine_prev_sibling, is_in_loop_body, is_in_token_of_for_loop,
+        previous_token, ImmediateLocation, ImmediatePrevSibling,
     },
     CompletionConfig,
 };
@@ -729,7 +729,7 @@ impl<'a> CompletionContext<'a> {
     ) {
         let fake_ident_token = file_with_fake_ident.token_at_offset(offset).right_biased().unwrap();
         let syntax_element = NodeOrToken::Token(fake_ident_token);
-        if for_is_prev2(syntax_element.clone()) {
+        if is_in_token_of_for_loop(syntax_element.clone()) {
             // for pat $0
             // there is nothing to complete here except `in` keyword
             // don't bother populating the context

crates/ide_completion/src/patterns.rs

@@ -11,7 +11,7 @@ use syntax::{
     ast::{self, HasArgList, HasLoopBody},
     match_ast, AstNode, Direction, SyntaxElement,
     SyntaxKind::*,
-    SyntaxNode, SyntaxToken, TextRange, TextSize, T,
+    SyntaxNode, SyntaxToken, TextRange, TextSize,
 };
 
 #[cfg(test)]
@@ -295,19 +295,37 @@ pub(crate) fn previous_token(element: SyntaxElement) -> Option<SyntaxToken> {
     element.into_token().and_then(previous_non_trivia_token)
 }
 
-/// Check if the token previous to the previous one is `for`.
-/// For example, `for _ i$0` => true.
-pub(crate) fn for_is_prev2(element: SyntaxElement) -> bool {
-    element
-        .into_token()
-        .and_then(previous_non_trivia_token)
-        .and_then(previous_non_trivia_token)
-        .filter(|it| it.kind() == T![for])
-        .is_some()
+pub(crate) fn is_in_token_of_for_loop(element: SyntaxElement) -> bool {
+    // oh my ...
+    (|| {
+        let syntax_token = element.into_token()?;
+        let range = syntax_token.text_range();
+        let for_expr = syntax_token.ancestors().find_map(ast::ForExpr::cast)?;
+
+        // check if the current token is the `in` token of a for loop
+        if let Some(token) = for_expr.in_token() {
+            return Some(syntax_token == token);
+        }
+        let pat = for_expr.pat()?;
+        if range.end() < pat.syntax().text_range().end() {
+            // if we are inside or before the pattern we can't be at the `in` token position
+            return None;
+        }
+        let next_sibl = next_non_trivia_sibling(pat.syntax().clone().into())?;
+        Some(match next_sibl {
+            // the loop body is some node, if our token is at the start we are at the `in` position,
+            // otherwise we could be in a recovered expression, we don't wanna ruin completions there
+            syntax::NodeOrToken::Node(n) => n.text_range().start() == range.start(),
+            // the loop body consists of a single token, if we are this we are certainly at the `in` token position
+            syntax::NodeOrToken::Token(t) => t == syntax_token,
+        })
+    })()
+    .unwrap_or(false)
 }
+
 #[test]
 fn test_for_is_prev2() {
-    check_pattern_is_applicable(r"for i i$0", for_is_prev2);
+    check_pattern_is_applicable(r"fn __() { for i i$0 }", is_in_token_of_for_loop);
 }
 
 pub(crate) fn is_in_loop_body(node: &SyntaxNode) -> bool {
@@ -329,7 +347,7 @@ pub(crate) fn is_in_loop_body(node: &SyntaxNode) -> bool {
 
 fn previous_non_trivia_token(token: SyntaxToken) -> Option<SyntaxToken> {
     let mut token = token.prev_token();
-    while let Some(inner) = token.clone() {
+    while let Some(inner) = token {
         if !inner.kind().is_trivia() {
             return Some(inner);
         } else {
@@ -339,6 +357,18 @@ fn previous_non_trivia_token(token: SyntaxToken) -> Option<SyntaxToken> {
     None
 }
 
+fn next_non_trivia_sibling(ele: SyntaxElement) -> Option<SyntaxElement> {
+    let mut e = ele.next_sibling_or_token();
+    while let Some(inner) = e {
+        if !inner.kind().is_trivia() {
+            return Some(inner);
+        } else {
+            e = inner.next_sibling_or_token();
+        }
+    }
+    None
+}
+
 #[cfg(test)]
 mod tests {
     use syntax::algo::find_node_at_offset;

crates/ide_completion/src/tests/item.rs

@@ -76,8 +76,14 @@ fn after_target_name_in_impl() {
             kw for
         "#]],
     );
-    // FIXME: This should emit `kw where`
-    check(r"impl Trait for Type $0", expect![[r#""#]]);
+    // FIXME: This should not emit `kw for`
+    check(
+        r"impl Trait for Type $0",
+        expect![[r#"
+        kw where
+        kw for
+    "#]],
+    );
 }
 
 #[test]

crates/ide_completion/src/tests/pattern.rs

@@ -92,6 +92,16 @@ fn quux() {
 "#,
         expect![[r#""#]],
     );
+    check_empty(
+        r#"
+fn foo() {
+    for &$0 in () {}
+}
+"#,
+        expect![[r#"
+            kw mut
+        "#]],
+    );
 }
 
 #[test]