1 files changed, 136 insertions, 0 deletions

diff --git a/crates/ra_ide/src/completion/complete_fn_param.rs b/crates/ra_ide/src/completion/complete_fn_param.rs
new file mode 100644
index 000000000..502458706
--- /dev/null
+++ b/crates/ra_ide/src/completion/complete_fn_param.rs
@@ -0,0 +1,136 @@
+//! FIXME: write short doc here
+
+use ra_syntax::{ast, match_ast, AstNode};
+use rustc_hash::FxHashMap;
+
+use crate::completion::{CompletionContext, CompletionItem, CompletionKind, Completions};
+
+/// Complete repeated parameters, 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.token.parent().ancestors() {
+        match_ast! {
+            match node {
+                ast::SourceFile(it) => { process(it, &mut params) },
+                ast::ItemList(it) => { process(it, &mut params) },
+                _ => (),
+            }
+        }
+    }
+    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, ctx.source_range(), label)
+                .lookup_by(lookup)
+                .add_to(acc)
+        });
+
+    fn process<N: ast::FnDefOwner>(node: N, params: &mut FxHashMap<String, (u32, 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::{do_completion, CompletionItem, CompletionKind};
+    use insta::assert_debug_snapshot;
+
+    fn do_magic_completion(code: &str) -> Vec<CompletionItem> {
+        do_completion(code, CompletionKind::Magic)
+    }
+
+    #[test]
+    fn test_param_completion_last_param() {
+        assert_debug_snapshot!(
+        do_magic_completion(
+                r"
+                fn foo(file_id: FileId) {}
+                fn bar(file_id: FileId) {}
+                fn baz(file<|>) {}
+                ",
+        ),
+            @r###"
+        [
+            CompletionItem {
+                label: "file_id: FileId",
+                source_range: [110; 114),
+                delete: [110; 114),
+                insert: "file_id: FileId",
+                lookup: "file_id",
+            },
+        ]
+        "###
+        );
+    }
+
+    #[test]
+    fn test_param_completion_nth_param() {
+        assert_debug_snapshot!(
+        do_magic_completion(
+                r"
+                fn foo(file_id: FileId) {}
+                fn bar(file_id: FileId) {}
+                fn baz(file<|>, x: i32) {}
+                ",
+        ),
+            @r###"
+        [
+            CompletionItem {
+                label: "file_id: FileId",
+                source_range: [110; 114),
+                delete: [110; 114),
+                insert: "file_id: FileId",
+                lookup: "file_id",
+            },
+        ]
+        "###
+        );
+    }
+
+    #[test]
+    fn test_param_completion_trait_param() {
+        assert_debug_snapshot!(
+        do_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###"
+        [
+            CompletionItem {
+                label: "file_id: FileId",
+                source_range: [289; 293),
+                delete: [289; 293),
+                insert: "file_id: FileId",
+                lookup: "file_id",
+            },
+        ]
+        "###
+        );
+    }
+}