LSP tests for TyFunctionDeclaration (FuelLabs#4031)

## Description
Adds go to definition and hover doc comment tests for the
`TyFunctionDeclaration` type.

While working on this I noticed we aren't collecting tokens in function
parameters and return type with generic types. I've opened up FuelLabs#4030 for
this to be addressed.

Works towards FuelLabs#3989

sway-lsp/tests/fixtures/tokens/functions/.gitignore

@@ -0,0 +1,2 @@
+out
+target

sway-lsp/tests/fixtures/tokens/functions/Forc.toml

@@ -0,0 +1,8 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "functions"
+
+[dependencies]
+std = { path = "../../../../../sway-lib-std" }

sway-lsp/tests/fixtures/tokens/functions/src/main.sw

@@ -0,0 +1,36 @@
+contract;
+
+struct Point {
+    x: u32,
+    y: u32,
+}
+
+/// A simple function declaration with a struct as a return type
+fn foo() -> Point {
+    Point { x: 1, y: 2 }
+}
+
+/// A function declaration with struct as a function parameter
+pub fn bar(p: Point) -> Point {
+    Point { x: p.x, y: p.y }
+}
+
+// Function expressions
+fn test() {
+    let p = foo();
+    let p2 = bar(p);
+}
+
+pub enum Rezult<T, E> {
+    Ok: T,
+    Err: E,
+}
+
+pub enum DumbError {
+    Error: (),
+}
+
+// Function with generic types
+pub fn func(r: Rezult<u8, DumbError>) -> Rezult<u8, DumbError> {
+    Rezult::Ok(1u8)
+}

sway-lsp/tests/lib.rs

@@ -197,6 +197,8 @@ async fn show_ast() {
     shutdown_and_exit(&mut service).await;
 }
 
+//------------------- GO TO DEFINITION -------------------//
+
 #[tokio::test]
 async fn go_to_definition() {
     let (mut service, _) = LspService::new(Backend::new);
@@ -777,6 +779,43 @@ async fn go_to_definition_for_consts() {
     definition_check_with_req_offset(&mut service, &mut go_to, 10, 17, 7).await;
 }
 
+#[tokio::test]
+async fn go_to_definition_for_functions() {
+    let (mut service, _) = LspService::new(Backend::new);
+    let uri = init_and_open(
+        &mut service,
+        test_fixtures_dir().join("tokens/functions/src/main.sw"),
+    )
+    .await;
+
+    let mut go_to = GotoDefintion {
+        req_uri: &uri,
+        req_line: 8,
+        req_char: 14,
+        def_line: 2,
+        def_start_char: 7,
+        def_end_char: 12,
+        def_path: uri.as_str(),
+    };
+    // Return type
+    let _ = lsp::definition_check(&mut service, &go_to, 1).await;
+
+    // TODO: @IGI-111 add test for generic return type
+
+    // Function parameter
+    definition_check_with_req_offset(&mut service, &mut go_to, 13, 16, 2).await;
+
+    // TODO: @IGI-111 add test for generic function parameter
+
+    // Functions expression
+    go_to.def_line = 8;
+    go_to.def_start_char = 3;
+    go_to.def_end_char = 6;
+    definition_check_with_req_offset(&mut service, &mut go_to, 19, 13, 3).await;
+}
+
+//------------------- HOVER DOCUMENTATION -------------------//
+
 #[tokio::test]
 async fn hover_docs_for_consts() {
     let (mut service, _) = LspService::new(Backend::new);
@@ -799,6 +838,24 @@ async fn hover_docs_for_consts() {
     let _ = lsp::hover_request(&mut service, &hover, 2).await;
 }
 
+#[tokio::test]
+async fn hover_docs_for_functions() {
+    let (mut service, _) = LspService::new(Backend::new);
+    let uri = init_and_open(
+        &mut service,
+        test_fixtures_dir().join("tokens/functions/src/main.sw"),
+    )
+    .await;
+
+    let hover = HoverDocumentation {
+        req_uri: &uri,
+        req_line: 20,
+        req_char: 14,
+        documentation: "```sway\npub fn bar(p: Point) -> Point\n```\n---\n A function declaration with struct as a function parameter",
+    };
+    let _ = lsp::hover_request(&mut service, &hover, 1).await;
+}
+
 #[tokio::test]
 async fn hover_docs_with_code_examples() {
     let (mut service, _) = LspService::new(Backend::new);