add docs and test

compiler-core/src/language_server/code_action.rs

@@ -3760,7 +3760,25 @@ fn pretty_constructor_name(
     }
 }
 
-/// .
+/// Builder for the "generate function" code action.
+/// Whenever someone hovers an invalid expression that is inferred to have a
+/// function type the language server can generate a function definition for it.
+/// For example:
+///
+/// ```gleam
+/// pub fn main() {
+///   wibble(1, 2, "hello")
+///  //  ^ [generate function]
+/// }
+/// ```
+///
+/// Will generate the following definition:
+///
+/// ```gleam
+/// pub fn wibble(arg_0: Int, arg_1: Int, arg_2: String) -> a {
+///   todo
+/// }
+/// ```
 ///
 pub struct GenerateFunction<'a> {
     module: &'a Module,

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

@@ -73,6 +73,7 @@ const EXPAND_FUNCTION_CAPTURE: &str = "Expand function capture";
 const GENERATE_DYNAMIC_DECODER: &str = "Generate dynamic decoder";
 const PATTERN_MATCH_ON_ARGUMENT: &str = "Pattern match on argument";
 const PATTERN_MATCH_ON_VARIABLE: &str = "Pattern match on variable";
+const GENERATE_FUNCTION: &str = "Generate function";
 
 macro_rules! assert_code_action {
     ($title:expr, $code:literal, $range:expr $(,)?) => {
@@ -4690,10 +4691,23 @@ fn map(list: List(a), fun: fn(a) -> b) { todo }
     );
 }
 
+#[test]
+fn generate_function_works_with_invalid_call() {
+    assert_code_action!(
+        GENERATE_FUNCTION,
+        "
+pub fn main() -> Bool {
+  wibble(1, True, 2.3)
+}
+",
+        find_position_of("wibble").to_selection()
+    );
+}
+
 #[test]
 fn generate_function_works_with_pipeline_steps() {
     assert_code_action!(
-        "Generate function",
+        GENERATE_FUNCTION,
         "
 pub fn main() {
   [1, 2, 3]
@@ -4712,7 +4726,7 @@ fn int_to_string(n: Int) -> String {
 #[test]
 fn generate_function_works_with_pipeline_steps_1() {
     assert_code_action!(
-        "Generate function",
+        GENERATE_FUNCTION,
         "
 pub fn main() {
   [1, 2, 3]

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

@@ -0,0 +1,21 @@
+---
+source: compiler-core/src/language_server/tests/action.rs
+expression: "\npub fn main() -> Bool {\n  wibble(1, True, 2.3)\n}\n"
+---
+----- BEFORE ACTION
+
+pub fn main() -> Bool {
+  wibble(1, True, 2.3)
+  ↑                   
+}
+
+
+----- AFTER ACTION
+
+pub fn main() -> Bool {
+  wibble(1, True, 2.3)
+}
+
+fn wibble(arg_1: Int, arg_2: Bool, arg_3: Float) -> Bool {
+  todo
+}