Skip to content

Fix unused type parameter checking to skip overload signatures and only report on implementations #1618

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 7 commits into
base: main
Choose a base branch
from
+181 −2
Open

Fix unused type parameter checking to skip overload signatures and only report on implementations #1618

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
c5eeeec
Initial plan
Copilot Aug 21, 2025
e72f01e
Initial investigation: add test case and understand issue
Copilot Aug 22, 2025
64269ce
Fix unused type parameter diagnostic to use TS6133 instead of TS6196
Copilot Aug 22, 2025
469d286
Add comprehensive test case for unused type parameters
Copilot Aug 22, 2025
c72979a
Revert diagnostic changes - type variables are not values that can be…
Copilot Aug 22, 2025
beefab7
Fix unused type parameter checking in overloads to only report on imp…
Copilot Aug 22, 2025
0065dbe
Combine comments for unused parameter and type parameter checking
Copilot Aug 22, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions internal/checker/checker.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6691,11 +6691,11 @@ func (c *Checker) checkUnusedIdentifiers(potentiallyUnusedIdentifiers []*ast.Nod
c.checkUnusedLocalsAndParameters(node)
case ast.KindConstructor, ast.KindFunctionExpression, ast.KindFunctionDeclaration, ast.KindArrowFunction, ast.KindMethodDeclaration,
ast.KindGetAccessor, ast.KindSetAccessor:
// Only report unused parameters on the implementation, not overloads.
// Only report unused parameters and type parameters on the implementation, not overloads.
if node.Body() != nil {
c.checkUnusedLocalsAndParameters(node)
c.checkUnusedTypeParameters(node)
}
c.checkUnusedTypeParameters(node)
case ast.KindMethodSignature, ast.KindCallSignature, ast.KindConstructSignature, ast.KindFunctionType, ast.KindConstructorType,
ast.KindTypeAliasDeclaration, ast.KindJSTypeAliasDeclaration, ast.KindInterfaceDeclaration:
c.checkUnusedTypeParameters(node)
Expand Down
24 changes: 24 additions & 0 deletions testdata/baselines/reference/compiler/overloadUnusedTypeParameters.errors.txt
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
overloadUnusedTypeParameters.ts(3,30): error TS6196: 'T' is declared but never used.
overloadUnusedTypeParameters.ts(13,31): error TS6196: 'T' is declared but never used.


==== overloadUnusedTypeParameters.ts (2 errors) ====
export function tryParseJson<T>(text: string): unknown;
export function tryParseJson<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson<T>() {
~
!!! error TS6196: 'T' is declared but never used.
throw new Error("noop")
}

export function tryParseJson2<T>(text: string): unknown;
export function tryParseJson2<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson2() {
throw new Error("noop")
}

export function tryParseJson3<T>(_text: string): unknown {
~
!!! error TS6196: 'T' is declared but never used.
throw new Error("noop")
}
29 changes: 29 additions & 0 deletions testdata/baselines/reference/compiler/overloadUnusedTypeParameters.js
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,29 @@
//// [tests/cases/compiler/overloadUnusedTypeParameters.ts] ////

//// [overloadUnusedTypeParameters.ts]
export function tryParseJson<T>(text: string): unknown;
export function tryParseJson<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson<T>() {
throw new Error("noop")
}

export function tryParseJson2<T>(text: string): unknown;
export function tryParseJson2<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson2() {
throw new Error("noop")
}

export function tryParseJson3<T>(_text: string): unknown {
throw new Error("noop")
}

//// [overloadUnusedTypeParameters.js]
export function tryParseJson() {
throw new Error("noop");
}
export function tryParseJson2() {
throw new Error("noop");
}
export function tryParseJson3(_text) {
throw new Error("noop");
}
56 changes: 56 additions & 0 deletions testdata/baselines/reference/compiler/overloadUnusedTypeParameters.symbols
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,56 @@
//// [tests/cases/compiler/overloadUnusedTypeParameters.ts] ////

=== overloadUnusedTypeParameters.ts ===
export function tryParseJson<T>(text: string): unknown;
>tryParseJson : Symbol(tryParseJson, Decl(overloadUnusedTypeParameters.ts, 0, 0), Decl(overloadUnusedTypeParameters.ts, 0, 55), Decl(overloadUnusedTypeParameters.ts, 1, 106))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 0, 29))
>text : Symbol(text, Decl(overloadUnusedTypeParameters.ts, 0, 32))

export function tryParseJson<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
>tryParseJson : Symbol(tryParseJson, Decl(overloadUnusedTypeParameters.ts, 0, 0), Decl(overloadUnusedTypeParameters.ts, 0, 55), Decl(overloadUnusedTypeParameters.ts, 1, 106))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 1, 29))
>text : Symbol(text, Decl(overloadUnusedTypeParameters.ts, 1, 32))
>predicate : Symbol(predicate, Decl(overloadUnusedTypeParameters.ts, 1, 45))
>parsed : Symbol(parsed, Decl(overloadUnusedTypeParameters.ts, 1, 58))
>parsed : Symbol(parsed, Decl(overloadUnusedTypeParameters.ts, 1, 58))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 1, 29))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 1, 29))

export function tryParseJson<T>() {
>tryParseJson : Symbol(tryParseJson, Decl(overloadUnusedTypeParameters.ts, 0, 0), Decl(overloadUnusedTypeParameters.ts, 0, 55), Decl(overloadUnusedTypeParameters.ts, 1, 106))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 2, 29))

throw new Error("noop")
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))
}

export function tryParseJson2<T>(text: string): unknown;
>tryParseJson2 : Symbol(tryParseJson2, Decl(overloadUnusedTypeParameters.ts, 4, 1), Decl(overloadUnusedTypeParameters.ts, 6, 56), Decl(overloadUnusedTypeParameters.ts, 7, 107))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 6, 30))
>text : Symbol(text, Decl(overloadUnusedTypeParameters.ts, 6, 33))

export function tryParseJson2<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
>tryParseJson2 : Symbol(tryParseJson2, Decl(overloadUnusedTypeParameters.ts, 4, 1), Decl(overloadUnusedTypeParameters.ts, 6, 56), Decl(overloadUnusedTypeParameters.ts, 7, 107))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 7, 30))
>text : Symbol(text, Decl(overloadUnusedTypeParameters.ts, 7, 33))
>predicate : Symbol(predicate, Decl(overloadUnusedTypeParameters.ts, 7, 46))
>parsed : Symbol(parsed, Decl(overloadUnusedTypeParameters.ts, 7, 59))
>parsed : Symbol(parsed, Decl(overloadUnusedTypeParameters.ts, 7, 59))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 7, 30))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 7, 30))

export function tryParseJson2() {
>tryParseJson2 : Symbol(tryParseJson2, Decl(overloadUnusedTypeParameters.ts, 4, 1), Decl(overloadUnusedTypeParameters.ts, 6, 56), Decl(overloadUnusedTypeParameters.ts, 7, 107))

throw new Error("noop")
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))
}

export function tryParseJson3<T>(_text: string): unknown {
>tryParseJson3 : Symbol(tryParseJson3, Decl(overloadUnusedTypeParameters.ts, 10, 1))
>T : Symbol(T, Decl(overloadUnusedTypeParameters.ts, 12, 30))
>_text : Symbol(_text, Decl(overloadUnusedTypeParameters.ts, 12, 33))

throw new Error("noop")
>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2022.error.d.ts, --, --))
}
50 changes: 50 additions & 0 deletions testdata/baselines/reference/compiler/overloadUnusedTypeParameters.types
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,50 @@
//// [tests/cases/compiler/overloadUnusedTypeParameters.ts] ////

=== overloadUnusedTypeParameters.ts ===
export function tryParseJson<T>(text: string): unknown;
>tryParseJson : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }
>text : string

export function tryParseJson<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
>tryParseJson : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }
>text : string
>predicate : (parsed: unknown) => parsed is T
>parsed : unknown

export function tryParseJson<T>() {
>tryParseJson : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }

throw new Error("noop")
>new Error("noop") : Error
>Error : ErrorConstructor
>"noop" : "noop"
}

export function tryParseJson2<T>(text: string): unknown;
>tryParseJson2 : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }
>text : string

export function tryParseJson2<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
>tryParseJson2 : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }
>text : string
>predicate : (parsed: unknown) => parsed is T
>parsed : unknown

export function tryParseJson2() {
>tryParseJson2 : { <T>(text: string): unknown; <T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined; }

throw new Error("noop")
>new Error("noop") : Error
>Error : ErrorConstructor
>"noop" : "noop"
}

export function tryParseJson3<T>(_text: string): unknown {
>tryParseJson3 : <T>(_text: string) => unknown
>_text : string

throw new Error("noop")
>new Error("noop") : Error
>Error : ErrorConstructor
>"noop" : "noop"
}
20 changes: 20 additions & 0 deletions testdata/tests/cases/compiler/overloadUnusedTypeParameters.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
// @strict: true
// @noUnusedLocals: true
// @noUnusedParameters: true
// @target: esnext

export function tryParseJson<T>(text: string): unknown;
export function tryParseJson<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson<T>() {
throw new Error("noop")
}

export function tryParseJson2<T>(text: string): unknown;
export function tryParseJson2<T>(text: string, predicate: (parsed: unknown) => parsed is T): T | undefined;
export function tryParseJson2() {
throw new Error("noop")
}

export function tryParseJson3<T>(_text: string): unknown {
throw new Error("noop")
}
Loading