Add inlay hints for function parameters (#6513)

## Description

Inlay hints are now displayed in function parameter locations if a
variable with the same name is not present. This should be identical to
the behaviour of rust-analyzer. The inlay_hints benchmark is slower
because we are now also calculating inlay hints for function_params and
variable decls in the same iteration. See screen shot below for all
supported types.

![Screenshot 2024-09-21 at 10 47
12 AM](https://github.com/user-attachments/assets/c3aaa901-e01d-4e88-a405-f1077d2d2dce)

closes #5196

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

sway-lsp/src/capabilities/inlay_hints.rs

@@ -7,13 +7,16 @@ use crate::{
 };
 use lsp_types::{self, Range, Url};
 use std::sync::Arc;
-use sway_core::{language::ty::TyDecl, type_system::TypeInfo};
-use sway_types::Spanned;
+use sway_core::{
+    language::ty::{TyDecl, TyExpression, TyExpressionVariant},
+    type_system::TypeInfo,
+};
+use sway_types::{Ident, Spanned};
 
-// Future PR's will add more kinds
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum InlayKind {
     TypeHint,
+    Parameter,
 }
 
 #[derive(Debug)]
@@ -23,81 +26,154 @@ pub struct InlayHint {
     pub label: String,
 }
 
+/// Generates inlay hints for the provided range.
 pub fn inlay_hints(
     session: Arc<Session>,
     uri: &Url,
     range: &Range,
     config: &InlayHintsConfig,
 ) -> Option<Vec<lsp_types::InlayHint>> {
-    let _p = tracing::trace_span!("inlay_hints").entered();
-    // 1. Loop through all our tokens and filter out all tokens that aren't TypedVariableDeclaration tokens
-    // 2. Also filter out all tokens that have a span that fall outside of the provided range
-    // 3. Filter out all variable tokens that have a type_ascription
-    // 4. Look up the type id for the remaining tokens
-    // 5. Convert the type into a string
+    let _span = tracing::trace_span!("inlay_hints").entered();
+
     if !config.type_hints {
         return None;
     }
 
+    // 1. Iterate through all tokens in the file
+    // 2. Filter for TypedVariableDeclaration tokens within the provided range
+    // 3. For each variable declaration:
+    //    a. If it's a function application, generate parameter hints
+    //    b. If it doesn't have a type ascription and its type is known:
+    //       - Look up the type information
+    //       - Generate a type hint
+    // 4. Collect all generated hints into a single vector
     let hints: Vec<lsp_types::InlayHint> = session
         .token_map()
         .tokens_for_file(uri)
         .filter_map(|item| {
             let token = item.value();
             token.typed.as_ref().and_then(|t| match t {
                 TypedAstToken::TypedDeclaration(TyDecl::VariableDecl(var_decl)) => {
-                    if var_decl.type_ascription.call_path_tree.is_some() {
-                        None
+                    let var_range = get_range_from_span(&var_decl.name.span());
+                    if var_range.start >= range.start && var_range.end <= range.end {
+                        Some(var_decl.clone())
                     } else {
-                        let var_range = get_range_from_span(&var_decl.name.span());
-                        if var_range.start >= range.start && var_range.end <= range.end {
-                            Some(var_decl.clone())
-                        } else {
-                            None
-                        }
+                        None
                     }
                 }
                 _ => None,
             })
         })
-        .filter_map(|var| {
-            let type_info = session.engines.read().te().get(var.type_ascription.type_id);
-            match &*type_info {
-                TypeInfo::Unknown | TypeInfo::UnknownGeneric { .. } => None,
-                _ => Some(var),
+        .flat_map(|var| {
+            let mut hints = Vec::new();
+
+            // Function parameter hints
+            if let TyExpressionVariant::FunctionApplication { arguments, .. } = &var.body.expression
+            {
+                hints.extend(handle_function_parameters(arguments, config));
             }
-        })
-        .map(|var| {
-            let range = get_range_from_span(&var.name.span());
-            let kind = InlayKind::TypeHint;
-            let label = format!("{}", session.engines.read().help_out(var.type_ascription));
-            let inlay_hint = InlayHint { range, kind, label };
-            self::inlay_hint(config.render_colons, inlay_hint)
+
+            // Variable declaration hints
+            if var.type_ascription.call_path_tree.is_none() {
+                let type_info = session.engines.read().te().get(var.type_ascription.type_id);
+                if !matches!(
+                    *type_info,
+                    TypeInfo::Unknown | TypeInfo::UnknownGeneric { .. }
+                ) {
+                    let range = get_range_from_span(&var.name.span());
+                    let kind = InlayKind::TypeHint;
+                    let label = format!("{}", session.engines.read().help_out(var.type_ascription));
+                    let inlay_hint = InlayHint { range, kind, label };
+                    hints.push(self::inlay_hint(config, inlay_hint));
+                }
+            }
+            hints
         })
         .collect();
 
     Some(hints)
 }
 
-fn inlay_hint(render_colons: bool, inlay_hint: InlayHint) -> lsp_types::InlayHint {
+fn handle_function_parameters(
+    arguments: &[(Ident, TyExpression)],
+    config: &InlayHintsConfig,
+) -> Vec<lsp_types::InlayHint> {
+    arguments
+        .iter()
+        .flat_map(|(name, exp)| {
+            let mut hints = Vec::new();
+            let (should_create_hint, span) = match &exp.expression {
+                TyExpressionVariant::Literal(_)
+                | TyExpressionVariant::ConstantExpression { .. }
+                | TyExpressionVariant::Tuple { .. }
+                | TyExpressionVariant::Array { .. }
+                | TyExpressionVariant::ArrayIndex { .. }
+                | TyExpressionVariant::FunctionApplication { .. }
+                | TyExpressionVariant::StructFieldAccess { .. }
+                | TyExpressionVariant::TupleElemAccess { .. } => (true, &exp.span),
+                TyExpressionVariant::EnumInstantiation {
+                    call_path_binding, ..
+                } => (true, &call_path_binding.span),
+                _ => (false, &exp.span),
+            };
+            if should_create_hint {
+                let range = get_range_from_span(span);
+                let kind = InlayKind::Parameter;
+                let label = name.as_str().to_string();
+                let inlay_hint = InlayHint { range, kind, label };
+                hints.push(self::inlay_hint(config, inlay_hint));
+            }
+            // Handle nested function applications
+            if let TyExpressionVariant::FunctionApplication {
+                arguments: nested_args,
+                ..
+            } = &exp.expression
+            {
+                hints.extend(handle_function_parameters(nested_args, config));
+            }
+            hints
+        })
+        .collect::<Vec<_>>()
+}
+
+fn inlay_hint(config: &InlayHintsConfig, inlay_hint: InlayHint) -> lsp_types::InlayHint {
+    let truncate_label = |label: String| -> String {
+        if let Some(max_length) = config.max_length {
+            if label.len() > max_length {
+                format!("{}...", &label[..max_length.saturating_sub(3)])
+            } else {
+                label
+            }
+        } else {
+            label
+        }
+    };
+
+    let label = match inlay_hint.kind {
+        InlayKind::TypeHint if config.render_colons => format!(": {}", inlay_hint.label),
+        InlayKind::Parameter if config.render_colons => format!("{}: ", inlay_hint.label),
+        _ => inlay_hint.label,
+    };
+
     lsp_types::InlayHint {
         position: match inlay_hint.kind {
             // after annotated thing
             InlayKind::TypeHint => inlay_hint.range.end,
+            InlayKind::Parameter => inlay_hint.range.start,
         },
-        label: lsp_types::InlayHintLabel::String(match inlay_hint.kind {
-            InlayKind::TypeHint if render_colons => format!(": {}", inlay_hint.label),
-            InlayKind::TypeHint => inlay_hint.label,
-        }),
+        label: lsp_types::InlayHintLabel::String(truncate_label(label)),
         kind: match inlay_hint.kind {
             InlayKind::TypeHint => Some(lsp_types::InlayHintKind::TYPE),
+            InlayKind::Parameter => Some(lsp_types::InlayHintKind::PARAMETER),
         },
         tooltip: None,
         padding_left: Some(match inlay_hint.kind {
-            InlayKind::TypeHint => !render_colons,
+            InlayKind::TypeHint => !config.render_colons,
+            InlayKind::Parameter => false,
         }),
         padding_right: Some(match inlay_hint.kind {
             InlayKind::TypeHint => false,
+            InlayKind::Parameter => !config.render_colons,
         }),
         text_edits: None,
         data: None,

sway-lsp/src/handlers/request.rs

@@ -333,7 +333,7 @@ pub async fn handle_semantic_tokens_full(
     }
 }
 
-pub(crate) async fn handle_inlay_hints(
+pub async fn handle_inlay_hints(
     state: &ServerState,
     params: InlayHintParams,
 ) -> Result<Option<Vec<InlayHint>>> {

sway-lsp/tests/fixtures/inlay_hints/.gitignore

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

sway-lsp/tests/fixtures/inlay_hints/Forc.toml

@@ -0,0 +1,9 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "inlay_hints"
+implicit-std = false
+
+[dependencies]
+std = { git = "https://github.com/FuelLabs/sway", tag = "v0.63.5" }

sway-lsp/tests/fixtures/inlay_hints/src/main.sw

@@ -0,0 +1,51 @@
+script;
+
+const CONSTANT: u64 = 42;
+
+enum MyEnum {
+    A: u64,
+}
+struct MyStruct {
+    a: u64,
+}
+fn my_function(foo: u64, bar: u64, long_argument_name: u64) -> u64 {
+    foo + bar + long_argument_name
+}
+fn identity<T>(x: T) -> T {
+    x
+}
+fn two_generics<A, B>(_a: A, b: B) -> B {
+    b
+}
+fn three_generics<A, B, C>(a: A, b: B, _c: C) -> B {
+    let _a: A = a;
+    b
+}
+
+fn main() {
+    let _x = my_function(1, 2, 3);
+    let foo = 1;
+    let _y = my_function(foo, 2, 3);
+    let bar = 2;
+    let _function_call = identity(my_function(1, bar, 3));
+    let _z = my_function(foo, bar, 3);
+    let long_argument_name = 3;
+    let _w = my_function(foo, bar, long_argument_name);
+    let _a: bool = identity(true);
+    let _b: u32 = identity(10u32);
+    let _c: u64 = identity(42);
+    let _e: str = identity("foo");
+    let _f: u64 = two_generics(true, 10);
+    let _g: str = three_generics(true, "foo", 10);
+    let _const = identity(CONSTANT);
+    let _tuple = identity((1, 2, 3));
+    let _array = identity([1, 2, 3]);
+    let _enum = identity(MyEnum::A(1));
+    let s = MyStruct { a: 1 };
+    let _struct_field_access = identity(s.a);
+    let t = (0, 1, 9);
+    let _tuple_elem_access = identity(t.2);
+    let a = [1, 2, 3];
+    let _array_index = identity(a[1]);
+}
+