Honor cfg attributes on params when lowering their patterns

crates/hir-def/src/body.rs

@@ -311,7 +311,20 @@ impl Body {
             DefWithBodyId::FunctionId(f) => {
                 let f = f.lookup(db);
                 let src = f.source(db);
-                params = src.value.param_list();
+                params = src.value.param_list().map(|param_list| {
+                    let item_tree = f.id.item_tree(db);
+                    let func = &item_tree[f.id.value];
+                    let krate = f.container.module(db).krate;
+                    let crate_graph = db.crate_graph();
+                    (
+                        param_list,
+                        func.params.clone().map(move |param| {
+                            item_tree
+                                .attrs(db, krate, param.into())
+                                .is_cfg_enabled(&crate_graph[krate].cfg_options)
+                        }),
+                    )
+                });
                 (src.file_id, f.module(db), src.value.body().map(ast::Expr::from))
             }
             DefWithBodyId::ConstId(c) => {
@@ -334,6 +347,7 @@ impl Body {
         let expander = Expander::new(db, file_id, module);
         let (mut body, source_map) = Body::new(db, expander, params, body);
         body.shrink_to_fit();
+
         (Arc::new(body), Arc::new(source_map))
     }
 
@@ -370,7 +384,7 @@ impl Body {
     fn new(
         db: &dyn DefDatabase,
         expander: Expander,
-        params: Option<ast::ParamList>,
+        params: Option<(ast::ParamList, impl Iterator<Item = bool>)>,
         body: Option<ast::Expr>,
     ) -> (Body, BodySourceMap) {
         lower::lower(db, expander, params, body)

crates/hir-def/src/body/lower.rs

@@ -77,7 +77,7 @@ impl<'a> LowerCtx<'a> {
 pub(super) fn lower(
     db: &dyn DefDatabase,
     expander: Expander,
-    params: Option<ast::ParamList>,
+    params: Option<(ast::ParamList, impl Iterator<Item = bool>)>,
     body: Option<ast::Expr>,
 ) -> (Body, BodySourceMap) {
     ExprCollector {
@@ -119,11 +119,13 @@ struct ExprCollector<'a> {
 impl ExprCollector<'_> {
     fn collect(
         mut self,
-        param_list: Option<ast::ParamList>,
+        param_list: Option<(ast::ParamList, impl Iterator<Item = bool>)>,
         body: Option<ast::Expr>,
     ) -> (Body, BodySourceMap) {
-        if let Some(param_list) = param_list {
-            if let Some(self_param) = param_list.self_param() {
+        if let Some((param_list, mut attr_enabled)) = param_list {
+            if let Some(self_param) =
+                param_list.self_param().filter(|_| attr_enabled.next().unwrap_or(false))
+            {
                 let ptr = AstPtr::new(&self_param);
                 let param_pat = self.alloc_pat(
                     Pat::Bind {
@@ -139,7 +141,11 @@ impl ExprCollector<'_> {
                 self.body.params.push(param_pat);
             }
 
-            for pat in param_list.params().filter_map(|param| param.pat()) {
+            for pat in param_list
+                .params()
+                .zip(attr_enabled)
+                .filter_map(|(param, enabled)| param.pat().filter(|_| enabled))
+            {
                 let param_pat = self.collect_pat(pat);
                 self.body.params.push(param_pat);
             }

crates/hir-ty/src/tests/patterns.rs

@@ -1070,3 +1070,13 @@ fn main() {
         "#,
     );
 }
+
+#[test]
+fn cfg_params() {
+    check_types(
+        r#"
+fn my_fn(#[cfg(feature = "feature")] u8: u8, u32: u32) {}
+                                           //^^^ u32
+"#,
+    );
+}

crates/ide-completion/src/context.rs

@@ -1,4 +1,4 @@
-//! See `CompletionContext` structure.
+//! See [`CompletionContext`] structure.
 
 mod analysis;
 #[cfg(test)]