Also prefer functions which return the expected type

Author: GearsDatapacks

compiler-core/src/language_server/completer.rs

@@ -136,6 +136,13 @@ impl<'a, IO> Completer<'a, IO> {
             // type is, which generally is the case.
             if expected_type.is_unbound() {
                 TypeMatch::Unknown
+            }
+            // We also want to prioritise functions which return the desired type,
+            // as often the user's intention will be to write a function call.
+            else if let Some((_, return_)) = type_.fn_types()
+                && expected_type.same_as(&return_)
+            {
+                TypeMatch::Matching
             } else if expected_type.same_as(type_) {
                 TypeMatch::Matching
             } else {

compiler-core/src/language_server/tests/completion.rs

@@ -2266,3 +2266,31 @@ pub fn main() -> Bool {
 
     assert_completion!(TestProject::for_source(code), Position::new(5, 3));
 }
+
+#[test]
+fn prefer_function_which_returns_expected_type() {
+    let code = "
+pub fn main() -> Int {
+  a
+}
+
+fn add(a, b) { a + b }
+fn sub(a, b) { a - b }
+fn addf(a, b) { a +. b }
+";
+
+    assert_completion!(TestProject::for_source(code), Position::new(2, 3));
+}
+
+#[test]
+fn prefer_function_which_returns_expected_generic_type() {
+    let code = "
+pub fn main() -> Result(Int, Nil) {
+  let result = Ok(12)
+  let result2 = Error(True)
+  r
+}
+";
+
+    assert_completion!(TestProject::for_source(code), Position::new(4, 3));
+}

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__argument_shadowing.snap

@@ -33,7 +33,7 @@ True
 main
   kind:   Function
   detail: fn(Int) -> fn(Float) -> a
-  sort:   2_main
+  sort:   02_main
   desc:   app
   edits:
     [3:0-3:0]: "main"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__local_variable_anonymous_function.snap

@@ -32,7 +32,7 @@ True
 main
   kind:   Function
   detail: fn() -> Int
-  sort:   2_main
+  sort:   02_main
   desc:   app
   edits:
     [2:34-2:34]: "main"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__local_variable_ignore_anonymous_function_args_nested.snap

@@ -36,15 +36,15 @@ True
 add_two
   kind:   Variable
   detail: fn(Int) -> Int
-  sort:   2_add_two
+  sort:   02_add_two
   desc:   app
   docs:   "A locally defined variable."
   edits:
     [5:4-5:4]: "add_two"
 main
   kind:   Function
   detail: fn() -> Int
-  sort:   2_main
+  sort:   02_main
   desc:   app
   edits:
     [5:4-5:4]: "main"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__local_variable_ignore_anonymous_function_returned.snap

@@ -35,7 +35,7 @@ True
 add_two
   kind:   Variable
   detail: fn(Int) -> Int
-  sort:   2_add_two
+  sort:   02_add_two
   desc:   app
   docs:   "A locally defined variable."
   edits:

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__local_variable_nested_anonymous_function.snap

@@ -36,7 +36,7 @@ True
 main
   kind:   Function
   detail: fn() -> Int
-  sort:   2_main
+  sort:   02_main
   desc:   app
   edits:
     [4:36-4:36]: "main"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__prefer_function_which_returns_expected_generic_type.snap

@@ -0,0 +1,55 @@
+---
+source: compiler-core/src/language_server/tests/completion.rs
+expression: "\npub fn main() -> Result(Int, Nil) {\n  let result = Ok(12)\n  let result2 = Error(True)\n  r\n}\n"
+---
+pub fn main() -> Result(Int, Nil) {
+  let result = Ok(12)
+  let result2 = Error(True)
+  r|
+}
+
+
+----- Completion content -----
+Error
+  kind:   Constructor
+  detail: gleam
+  sort:   04_Error
+False
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_False
+Nil
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_Nil
+Ok
+  kind:   Constructor
+  detail: gleam
+  sort:   04_Ok
+True
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_True
+main
+  kind:   Function
+  detail: fn() -> Result(Int, Nil)
+  sort:   02_main
+  desc:   app
+  edits:
+    [4:2-4:2]: "main"
+result
+  kind:   Variable
+  detail: Result(Int, a)
+  sort:   02_result
+  desc:   app
+  docs:   "A locally defined variable."
+  edits:
+    [4:2-4:2]: "result"
+result2
+  kind:   Variable
+  detail: Result(a, Bool)
+  sort:   2_result2
+  desc:   app
+  docs:   "A locally defined variable."
+  edits:
+    [4:2-4:2]: "result2"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__prefer_function_which_returns_expected_type.snap

@@ -0,0 +1,62 @@
+---
+source: compiler-core/src/language_server/tests/completion.rs
+expression: "\npub fn main() -> Int {\n  a\n}\n\nfn add(a, b) { a + b }\nfn sub(a, b) { a - b }\nfn addf(a, b) { a +. b }\n"
+---
+pub fn main() -> Int {
+  a|
+}
+
+fn add(a, b) { a + b }
+fn sub(a, b) { a - b }
+fn addf(a, b) { a +. b }
+
+
+----- Completion content -----
+Error
+  kind:   Constructor
+  detail: gleam
+  sort:   4_Error
+False
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_False
+Nil
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_Nil
+Ok
+  kind:   Constructor
+  detail: gleam
+  sort:   4_Ok
+True
+  kind:   EnumMember
+  detail: gleam
+  sort:   4_True
+add
+  kind:   Function
+  detail: fn(Int, Int) -> Int
+  sort:   02_add
+  desc:   app
+  edits:
+    [2:2-2:2]: "add"
+addf
+  kind:   Function
+  detail: fn(Float, Float) -> Float
+  sort:   2_addf
+  desc:   app
+  edits:
+    [2:2-2:2]: "addf"
+main
+  kind:   Function
+  detail: fn() -> Int
+  sort:   02_main
+  desc:   app
+  edits:
+    [2:2-2:2]: "main"
+sub
+  kind:   Function
+  detail: fn(Int, Int) -> Int
+  sort:   02_sub
+  desc:   app
+  edits:
+    [2:2-2:2]: "sub"

compiler-core/src/language_server/tests/snapshots/gleam_core__language_server__tests__completion__prefer_values_matching_expected_type.snap

@@ -34,7 +34,7 @@ True
 main
   kind:   Function
   detail: fn() -> Bool
-  sort:   2_main
+  sort:   02_main
   desc:   app
   edits:
     [5:2-5:2]: "main"