feat(formatter): implement formatting for TSTypeParameters and TSTypeParameterInstantiation (#13919)

Dunqing · Dunqing · commit 06a1df69907c · 2025-09-22T04:24:15.000Z
diff --git a/crates/oxc_formatter/src/write/arrow_function_expression.rs b/crates/oxc_formatter/src/write/arrow_function_expression.rs
@@ -855,22 +855,15 @@ fn format_signature<'a, 'b>(
     cache_mode: FunctionBodyCacheMode,
 ) -> impl Format<'a> + 'b {
     format_with(move |f| {
-        let formatted_async_token =
-            format_with(|f| if arrow.r#async() { write!(f, ["async", space()]) } else { Ok(()) });
-
-        let formatted_parameters =
-            format_with(|f| write!(f, [arrow.type_parameters(), arrow.params()]));
-
-        let format_return_type = format_with(|f| write!(f, arrow.return_type()));
-
         let signatures = format_once(|f| {
             write!(
                 f,
                 [group(&format_args!(
                     maybe_space(!is_first_in_chain),
-                    formatted_async_token,
-                    group(&formatted_parameters),
-                    group(&format_return_type)
+                    arrow.r#async().then_some("async "),
+                    arrow.type_parameters(),
+                    arrow.params(),
+                    group(&arrow.return_type())
                 ))]
             )
         });
diff --git a/crates/oxc_formatter/src/write/class.rs b/crates/oxc_formatter/src/write/class.rs
@@ -27,7 +27,7 @@ use crate::{
 
 use super::{
     FormatWrite,
-    type_parameters::{FormatTsTypeParameters, FormatTsTypeParametersOptions},
+    type_parameters::{FormatTSTypeParameters, FormatTSTypeParametersOptions},
 };
 
 impl<'a> FormatWrite<'a> for AstNode<'a, ClassBody<'a>> {
@@ -314,9 +314,9 @@ impl<'a> Format<'a> for FormatClass<'a, '_> {
             if let Some(type_parameters) = &type_parameters {
                 write!(
                     f,
-                    FormatTsTypeParameters::new(
+                    FormatTSTypeParameters::new(
                         type_parameters,
-                        FormatTsTypeParametersOptions {
+                        FormatTSTypeParametersOptions {
                             group_id: type_parameters_id,
                             is_type_or_interface_decl: false
                         }
diff --git a/crates/oxc_formatter/src/write/function.rs b/crates/oxc_formatter/src/write/function.rs
@@ -49,6 +49,7 @@ impl<'a> FormatWrite<'a> for FormatFunction<'a, '_> {
         if self.r#async() {
             write!(f, ["async", space()])?;
         }
+
         write!(
             f,
             [
diff --git a/crates/oxc_formatter/src/write/mod.rs b/crates/oxc_formatter/src/write/mod.rs
@@ -78,7 +78,7 @@ use self::{
     object_pattern_like::ObjectPatternLike,
     parameter_list::{ParameterLayout, ParameterList},
     semicolon::{ClassPropertySemicolon, OptionalSemicolon},
-    type_parameters::{FormatTsTypeParameters, FormatTsTypeParametersOptions},
+    type_parameters::{FormatTSTypeParameters, FormatTSTypeParametersOptions},
     utils::{
         array::{TrailingSeparatorMode, write_array_node},
         statement_body::FormatStatementBody,
@@ -1377,44 +1377,9 @@ impl<'a> FormatWrite<'a> for AstNode<'a, TSQualifiedName<'a>> {
     }
 }
 
-impl<'a> FormatWrite<'a> for AstNode<'a, TSTypeParameterInstantiation<'a>> {
-    fn write(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
-        write!(f, "<")?;
-        for (i, param) in self.params().iter().enumerate() {
-            if i != 0 {
-                write!(f, [",", space()])?;
-            }
-            write!(f, param)?;
-        }
-        write!(f, ">")
-    }
-}
-
-impl<'a> FormatWrite<'a> for AstNode<'a, TSTypeParameter<'a>> {
-    fn write(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
-        if self.r#const() {
-            write!(f, ["const", space()])?;
-        }
-        if self.r#in() {
-            write!(f, ["in", space()])?;
-        }
-        if self.out() {
-            write!(f, ["out", space()])?;
-        }
-        write!(f, self.name())?;
-        if let Some(constraint) = &self.constraint() {
-            write!(f, [space(), "extends", space(), constraint])?;
-        }
-        if let Some(default) = &self.default() {
-            write!(f, [space(), "=", space(), default])?;
-        }
-        Ok(())
-    }
-}
-
 impl<'a> FormatWrite<'a> for AstNode<'a, TSTypeParameterDeclaration<'a>> {
     fn write(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
-        write!(f, ["<", self.params(), ">"])
+        FormatTSTypeParameters::new(self, FormatTSTypeParametersOptions::default()).fmt(f)
     }
 }
 
@@ -1463,9 +1428,9 @@ impl<'a> FormatWrite<'a> for AstNode<'a, TSInterfaceDeclaration<'a>> {
             if let Some(type_parameters) = type_parameters {
                 write!(
                     f,
-                    FormatTsTypeParameters::new(
+                    FormatTSTypeParameters::new(
                         type_parameters,
-                        FormatTsTypeParametersOptions {
+                        FormatTSTypeParametersOptions {
                             group_id: type_parameter_group,
                             is_type_or_interface_decl: true
                         }
diff --git a/crates/oxc_formatter/src/write/type_parameters.rs b/crates/oxc_formatter/src/write/type_parameters.rs
@@ -1,3 +1,5 @@
+use std::fmt::Pointer;
+
 use oxc_allocator::{Address, Vec};
 use oxc_ast::{AstKind, ast::*};
 
@@ -9,9 +11,49 @@ use crate::{
     },
     generated::ast_nodes::{AstNode, AstNodes},
     options::{FormatTrailingCommas, TrailingSeparator},
+    utils::call_expression::is_test_call_expression,
     write,
 };
 
+use super::FormatWrite;
+
+impl<'a> FormatWrite<'a> for AstNode<'a, TSTypeParameter<'a>> {
+    fn write(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
+        if self.r#const() {
+            write!(f, ["const", space()])?;
+        }
+        if self.r#in() {
+            write!(f, ["in", space()])?;
+        }
+        if self.out() {
+            write!(f, ["out", space()])?;
+        }
+        write!(f, self.name())?;
+
+        if let Some(constraint) = &self.constraint() {
+            let group_id = f.group_id("constraint");
+
+            write!(
+                f,
+                [
+                    space(),
+                    "extends",
+                    group(&indent(&format_args!(
+                        line_suffix_boundary(),
+                        soft_line_break_or_space()
+                    )))
+                    .with_group_id(Some(group_id)),
+                    indent_if_group_breaks(&constraint, group_id)
+                ]
+            )?;
+        }
+        if let Some(default) = &self.default() {
+            write!(f, [space(), "=", space(), default])?;
+        }
+        Ok(())
+    }
+}
+
 impl<'a> Format<'a> for AstNode<'a, Vec<'a, TSTypeParameter<'a>>> {
     fn fmt(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
         // Type parameter lists of arrow function expressions have to include at least one comma
@@ -37,35 +79,190 @@ impl<'a> Format<'a> for AstNode<'a, Vec<'a, TSTypeParameter<'a>>> {
     }
 }
 
-pub struct FormatTsTypeParametersOptions {
+#[derive(Default)]
+pub struct FormatTSTypeParametersOptions {
     pub group_id: Option<GroupId>,
     pub is_type_or_interface_decl: bool,
 }
 
-pub struct FormatTsTypeParameters<'a, 'b> {
+pub struct FormatTSTypeParameters<'a, 'b> {
     decl: &'b AstNode<'a, TSTypeParameterDeclaration<'a>>,
-    options: FormatTsTypeParametersOptions,
+    options: FormatTSTypeParametersOptions,
 }
 
-impl<'a, 'b> FormatTsTypeParameters<'a, 'b> {
+impl<'a, 'b> FormatTSTypeParameters<'a, 'b> {
     pub fn new(
         decl: &'b AstNode<'a, TSTypeParameterDeclaration<'a>>,
-        options: FormatTsTypeParametersOptions,
+        options: FormatTSTypeParametersOptions,
     ) -> Self {
         Self { decl, options }
     }
 }
 
-impl<'a> Format<'a> for FormatTsTypeParameters<'a, '_> {
+impl<'a> Format<'a> for FormatTSTypeParameters<'a, '_> {
     fn fmt(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
-        if self.decl.params().is_empty() && self.options.is_type_or_interface_decl {
+        let params = self.decl.params();
+        if params.is_empty() && self.options.is_type_or_interface_decl {
             write!(f, "<>")
         } else {
             write!(
                 f,
-                [group(&format_args!("<", soft_block_indent(&self.decl.params()), ">"))
+                [group(&format_args!("<", format_once(|f| {
+                    if matches!( self.decl.parent.parent().parent(), AstNodes::CallExpression(call) if is_test_call_expression(call))
+                    {
+                        f.join_nodes_with_space().entries_with_trailing_separator(params, ",", TrailingSeparator::Omit).finish()
+                    } else {
+                        soft_block_indent(&params).fmt(f)
+                    }
+                }), ">"))
                     .with_group_id(self.options.group_id)]
             )
         }
     }
 }
+
+impl<'a> FormatWrite<'a> for AstNode<'a, TSTypeParameterInstantiation<'a>> {
+    fn write(&self, f: &mut Formatter<'_, 'a>) -> FormatResult<()> {
+        let params = self.params();
+
+        if params.is_empty() {
+            // This shouldn't happen in valid TypeScript code, but handle it gracefully
+            return write!(
+                f,
+                [&group(&format_args!(
+                    "<",
+                    format_dangling_comments(self.span).with_soft_block_indent(),
+                    ">"
+                ))]
+            );
+        }
+
+        // Check if this is in the context of an arrow function variable
+        let is_arrow_function_vars = is_arrow_function_variable_type_argument(self);
+
+        // Check if the first (and only) argument can be hugged
+        let first_arg_can_be_hugged = if params.len() == 1 {
+            if let Some(first_type) = params.first() {
+                matches!(first_type.as_ref(), TSType::TSNullKeyword(_))
+                    || should_hug_single_type(first_type.as_ref())
+            } else {
+                false
+            }
+        } else {
+            false
+        };
+
+        let format_params = format_once(|f| {
+            f.join_with(&soft_line_break_or_space())
+                .entries_with_trailing_separator(params, ",", TrailingSeparator::Disallowed)
+                .finish()
+        });
+
+        let should_inline =
+            !is_arrow_function_vars && (params.is_empty() || first_arg_can_be_hugged);
+
+        if should_inline {
+            write!(f, ["<", format_params, ">"])
+        } else {
+            write!(f, [group(&format_args!("<", soft_block_indent(&format_params), ">"))])
+        }
+    }
+}
+
+/// Check if a TSType is a simple type (primitives, keywords, simple references)
+fn is_simple_type(ty: &TSType) -> bool {
+    match ty {
+        TSType::TSAnyKeyword(_)
+        | TSType::TSNullKeyword(_)
+        | TSType::TSThisType(_)
+        | TSType::TSVoidKeyword(_)
+        | TSType::TSNumberKeyword(_)
+        | TSType::TSBooleanKeyword(_)
+        | TSType::TSBigIntKeyword(_)
+        | TSType::TSStringKeyword(_)
+        | TSType::TSSymbolKeyword(_)
+        | TSType::TSNeverKeyword(_)
+        | TSType::TSObjectKeyword(_)
+        | TSType::TSUndefinedKeyword(_)
+        | TSType::TSTemplateLiteralType(_)
+        | TSType::TSLiteralType(_)
+        | TSType::TSUnknownKeyword(_) => true,
+        TSType::TSTypeReference(reference) => {
+            // Simple reference without type arguments
+            reference.type_arguments.is_none()
+        }
+        _ => false,
+    }
+}
+
+/// Check if a TSType is object-like (object literal, mapped type, etc.)
+fn is_object_like_type(ty: &TSType) -> bool {
+    matches!(ty, TSType::TSTypeLiteral(_) | TSType::TSMappedType(_))
+}
+
+/// Check if a single type should be "hugged" (kept inline)
+fn should_hug_single_type(ty: &TSType) -> bool {
+    // Simple types and object-like types can be hugged
+    if is_simple_type(ty) || is_object_like_type(ty) {
+        return true;
+    }
+
+    // Check for union types with mostly void types and one object type
+    // (e.g., `SomeType<ObjectType | null | undefined>`)
+    if let TSType::TSUnionType(union_type) = ty {
+        let types = &union_type.types;
+
+        // Must have at least 2 types
+        if types.len() < 2 {
+            return types.len() == 1 && should_hug_single_type(&types[0]);
+        }
+
+        let has_object_type = types
+            .iter()
+            .any(|t| matches!(t, TSType::TSTypeLiteral(_) | TSType::TSTypeReference(_)));
+
+        let void_count = types
+            .iter()
+            .filter(|t| {
+                matches!(
+                    t,
+                    TSType::TSVoidKeyword(_)
+                        | TSType::TSNullKeyword(_)
+                        | TSType::TSUndefinedKeyword(_)
+                )
+            })
+            .count();
+
+        // Union is huggable if it's mostly void types with one object/reference type
+        (types.len() - 1 == void_count && has_object_type) || types.len() == 1
+    } else {
+        false
+    }
+}
+
+/// Check if this type parameter instantiation is in an arrow function variable context
+///
+/// This detects patterns like:
+/// ```typescript
+/// const foo: SomeThing<{ [P in "x" | "y"]: number }> = () => {};
+/// ```
+fn is_arrow_function_variable_type_argument<'a>(
+    node: &AstNode<'a, TSTypeParameterInstantiation<'a>>,
+) -> bool {
+    let Some(first) = node.params().first() else { unreachable!() };
+
+    // Skip check for single object-like types
+    if node.params().len() == 1 && is_object_like_type(first.as_ref()) {
+        return false;
+    }
+
+    matches!(
+        &node.parent,
+        AstNodes::TSTypeAnnotation(type_annotation)
+            if matches!(
+                &type_annotation.parent,
+                AstNodes::VariableDeclarator(var_decl)
+                    if matches!(&var_decl.init, Some(Expression::ArrowFunctionExpression(_)))
+            )
+    )
+}
diff --git a/tasks/coverage/snapshots/formatter_typescript.snap b/tasks/coverage/snapshots/formatter_typescript.snap
@@ -2,7 +2,7 @@ commit: 261630d6
 
 formatter_typescript Summary:
 AST Parsed     : 8816/8816 (100.00%)
-Positive Passed: 8788/8816 (99.68%)
+Positive Passed: 8789/8816 (99.69%)
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/amdLikeInputDeclarationEmit.ts
 
 Expect to Parse: tasks/coverage/typescript/tests/cases/compiler/arrayFromAsync.ts
@@ -15,8 +15,6 @@ Mismatch: tasks/coverage/typescript/tests/cases/compiler/complexNarrowingWithAny
 
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/declarationEmitCastReusesTypeNode4.ts
 
-Mismatch: tasks/coverage/typescript/tests/cases/compiler/declarationEmitShadowingInferNotRenamed.ts
-
 Expect to Parse: tasks/coverage/typescript/tests/cases/compiler/genericTypeAssertions3.ts
 Unexpected token
 Mismatch: tasks/coverage/typescript/tests/cases/compiler/jsxNamespaceGlobalReexport.tsx
diff --git a/tasks/prettier_conformance/snapshots/prettier.ts.snap.md b/tasks/prettier_conformance/snapshots/prettier.ts.snap.md

Original file line number	Diff line number	Diff line change
`@@ -49,6 +49,7 @@ impl<'a> FormatWrite<'a> for FormatFunction<'a, '_> {`
`49`	`49`	`if self.r#async() {`
`50`	`50`	`write!(f, ["async", space()])?;`
`51`	`51`	`}`
	`52`	`+`
`52`	`53`	`write!(`
`53`	`54`	`f,`
`54`	`55`	`[`