Take number of arguments at the call-site into account for signature help

Fixes #1065

1 files changed, 22 insertions, 1 deletions

diff --git a/crates/ra_ide_api/src/call_info.rs b/crates/ra_ide_api/src/call_info.rs
index c5e8d5843..831c4ad12 100644
--- a/crates/ra_ide_api/src/call_info.rs
+++ b/crates/ra_ide_api/src/call_info.rs
@@ -28,6 +28,7 @@ pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<Cal
     let function = hir::source_binder::function_from_source(db, symbol.file_id, fn_def)?;
 
     let mut call_info = CallInfo::new(db, function, fn_def)?;
+
     // If we have a calling expression let's find which argument we are on
     let num_params = call_info.parameters.len();
     let has_self = fn_def.param_list().and_then(|l| l.self_param()).is_some();
@@ -38,7 +39,15 @@ pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<Cal
         }
     } else if num_params > 1 {
         // Count how many parameters into the call we are.
-        if let Some(ref arg_list) = calling_node.arg_list() {
+        if let Some(arg_list) = calling_node.arg_list() {
+            // Number of arguments specified at the caller site
+            let mut num_args_of_call = arg_list.args().count();
+
+            // If we are calling a method account for the `self` argument.
+            if has_self {
+                num_args_of_call = num_args_of_call + 1;
+            }
+
             let arg_list_range = arg_list.syntax().range();
             if !arg_list_range.contains_inclusive(position.offset) {
                 tested_by!(call_info_bad_offset);
@@ -49,6 +58,7 @@ pub(crate) fn call_info(db: &RootDatabase, position: FilePosition) -> Option<Cal
                 .args()
                 .position(|arg| arg.syntax().range().contains(position.offset))
                 .or(Some(num_params - 1))
+                .min(Some(num_args_of_call))
                 .unwrap();
 
             call_info.active_parameter = Some(param);
@@ -156,6 +166,17 @@ fn bar() { foo(3, <|>); }"#,
     }
 
     #[test]
+    fn test_fn_signature_two_args_empty() {
+        let info = call_info(
+            r#"fn foo(x: u32, y: u32) -> u32 {x + y}
+fn bar() { foo(<|>); }"#,
+        );
+
+        assert_eq!(info.parameters, vec!("x".to_string(), "y".to_string()));
+        assert_eq!(info.active_parameter, Some(0));
+    }
+
+    #[test]
     fn test_fn_signature_for_impl() {
         let info = call_info(
             r#"struct F; impl F { pub fn new() { F{}} }