1 files changed, 102 insertions, 0 deletions

diff --git a/crates/ra_ide_api/src/completion/complete_fn_param.rs b/crates/ra_ide_api/src/completion/complete_fn_param.rs
new file mode 100644
index 000000000..c1739e47e
--- /dev/null
+++ b/crates/ra_ide_api/src/completion/complete_fn_param.rs
@@ -0,0 +1,102 @@
+use ra_syntax::{
+    algo::visit::{visitor_ctx, VisitorCtx},
+    ast,
+    AstNode,
+};
+use rustc_hash::FxHashMap;
+
+use crate::completion::{CompletionContext, Completions, CompletionKind, CompletionItem};
+
+/// Complete repeated parametes, both name and type. For example, if all
+/// functions in a file have a `spam: &mut Spam` parameter, a completion with
+/// `spam: &mut Spam` insert text/label and `spam` lookup string will be
+/// suggested.
+pub(super) fn complete_fn_param(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.is_param {
+        return;
+    }
+
+    let mut params = FxHashMap::default();
+    for node in ctx.leaf.ancestors() {
+        let _ = visitor_ctx(&mut params)
+            .visit::<ast::SourceFile, _>(process)
+            .visit::<ast::ItemList, _>(process)
+            .accept(node);
+    }
+    params
+        .into_iter()
+        .filter_map(|(label, (count, param))| {
+            let lookup = param.pat()?.syntax().text().to_string();
+            if count < 2 {
+                None
+            } else {
+                Some((label, lookup))
+            }
+        })
+        .for_each(|(label, lookup)| {
+            CompletionItem::new(CompletionKind::Magic, label)
+                .lookup_by(lookup)
+                .add_to(acc)
+        });
+
+    fn process<'a, N: ast::FnDefOwner>(
+        node: &'a N,
+        params: &mut FxHashMap<String, (u32, &'a ast::Param)>,
+    ) {
+        node.functions()
+            .filter_map(|it| it.param_list())
+            .flat_map(|it| it.params())
+            .for_each(|param| {
+                let text = param.syntax().text().to_string();
+                params.entry(text).or_insert((0, param)).0 += 1;
+            })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::completion::*;
+
+    fn check_magic_completion(code: &str, expected_completions: &str) {
+        check_completion(code, expected_completions, CompletionKind::Magic);
+    }
+
+    #[test]
+    fn test_param_completion_last_param() {
+        check_magic_completion(
+            r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>) {}
+            ",
+            r#"file_id "file_id: FileId""#,
+        );
+    }
+
+    #[test]
+    fn test_param_completion_nth_param() {
+        check_magic_completion(
+            r"
+            fn foo(file_id: FileId) {}
+            fn bar(file_id: FileId) {}
+            fn baz(file<|>, x: i32) {}
+            ",
+            r#"file_id "file_id: FileId""#,
+        );
+    }
+
+    #[test]
+    fn test_param_completion_trait_param() {
+        check_magic_completion(
+            r"
+            pub(crate) trait SourceRoot {
+                pub fn contains(&self, file_id: FileId) -> bool;
+                pub fn module_map(&self) -> &ModuleMap;
+                pub fn lines(&self, file_id: FileId) -> &LineIndex;
+                pub fn syntax(&self, file<|>)
+            }
+            ",
+            r#"file_id "file_id: FileId""#,
+        );
+    }
+}