Support deleting all unused type parameters in a list, and deleting @template tag (#25748)

* Support deleting all unused type parameters in a list, and deleting @template tag

* Support type parameter in 'infer'

src/compiler/checker.ts

@@ -22613,6 +22613,7 @@ namespace ts {
                 grammarErrorOnNode(node, Diagnostics.infer_declarations_are_only_permitted_in_the_extends_clause_of_a_conditional_type);
             }
             checkSourceElement(node.typeParameter);
+            registerForUnusedIdentifiersCheck(node);
         }
 
         function checkImportType(node: ImportTypeNode) {
@@ -23641,7 +23642,8 @@ namespace ts {
         type PotentiallyUnusedIdentifier =
             | SourceFile | ModuleDeclaration | ClassLikeDeclaration | InterfaceDeclaration
             | Block | CaseBlock | ForStatement | ForInStatement | ForOfStatement
-            | Exclude<SignatureDeclaration, IndexSignatureDeclaration | JSDocFunctionType> | TypeAliasDeclaration;
+            | Exclude<SignatureDeclaration, IndexSignatureDeclaration | JSDocFunctionType> | TypeAliasDeclaration
+            | InferTypeNode;
 
         function checkUnusedIdentifiers(potentiallyUnusedIdentifiers: ReadonlyArray<PotentiallyUnusedIdentifier>, addDiagnostic: AddUnusedDiagnostic) {
             for (const node of potentiallyUnusedIdentifiers) {
@@ -23681,6 +23683,7 @@ namespace ts {
                     case SyntaxKind.FunctionType:
                     case SyntaxKind.ConstructorType:
                     case SyntaxKind.TypeAliasDeclaration:
+                    case SyntaxKind.InferType:
                         checkUnusedTypeParameters(node, addDiagnostic);
                         break;
                     default:
@@ -23734,21 +23737,48 @@ namespace ts {
             }
         }
 
-        function checkUnusedTypeParameters(
-            node: ClassDeclaration | ClassExpression | FunctionDeclaration | MethodDeclaration | FunctionExpression | ArrowFunction | ConstructorDeclaration | SignatureDeclaration | InterfaceDeclaration | TypeAliasDeclaration,
-            addDiagnostic: AddUnusedDiagnostic,
-        ): void {
+        function checkUnusedTypeParameters(node: ClassLikeDeclaration | SignatureDeclaration | InterfaceDeclaration | TypeAliasDeclaration | InferTypeNode, addDiagnostic: AddUnusedDiagnostic): void {
             // Only report errors on the last declaration for the type parameter container;
             // this ensures that all uses have been accounted for.
-            const typeParameters = getEffectiveTypeParameterDeclarations(node);
-            if (!(node.flags & NodeFlags.Ambient) && last(getSymbolOfNode(node).declarations) === node) {
+            if (node.flags & NodeFlags.Ambient || node.kind !== SyntaxKind.InferType && last(getSymbolOfNode(node).declarations) !== node) return;
+
+            if (node.kind === SyntaxKind.InferType) {
+                const { typeParameter } = node;
+                if (isTypeParameterUnused(typeParameter)) {
+                    addDiagnostic(node, UnusedKind.Parameter, createDiagnosticForNode(node, Diagnostics._0_is_declared_but_its_value_is_never_read, idText(typeParameter.name)));
+                }
+            }
+            else {
+                const typeParameters = getEffectiveTypeParameterDeclarations(node);
+                const seenParentsWithEveryUnused = new NodeSet<DeclarationWithTypeParameterChildren>();
+
                 for (const typeParameter of typeParameters) {
-                    if (!(getMergedSymbol(typeParameter.symbol).isReferenced! & SymbolFlags.TypeParameter) && !isIdentifierThatStartsWithUnderscore(typeParameter.name)) {
-                        addDiagnostic(typeParameter, UnusedKind.Parameter, createDiagnosticForNode(typeParameter.name, Diagnostics._0_is_declared_but_its_value_is_never_read, symbolName(typeParameter.symbol)));
+                    if (!isTypeParameterUnused(typeParameter)) continue;
+
+                    const name = idText(typeParameter.name);
+                    const { parent } = typeParameter;
+                    if (parent.kind !== SyntaxKind.InferType && parent.typeParameters!.every(isTypeParameterUnused)) {
+                        if (seenParentsWithEveryUnused.tryAdd(parent)) {
+                            const range = isJSDocTemplateTag(parent)
+                                // Whole @template tag
+                                ? rangeOfNode(parent)
+                                // Include the `<>` in the error message
+                                : rangeOfTypeParameters(parent.typeParameters!);
+                            const only = typeParameters.length === 1;
+                            const message = only ? Diagnostics._0_is_declared_but_its_value_is_never_read : Diagnostics.All_type_parameters_are_unused;
+                            const arg0 = only ? name : undefined;
+                            addDiagnostic(typeParameter, UnusedKind.Parameter, createFileDiagnostic(getSourceFileOfNode(parent), range.pos, range.end - range.pos, message, arg0));
+                        }
+                    }
+                    else {
+                        addDiagnostic(typeParameter, UnusedKind.Parameter, createDiagnosticForNode(typeParameter, Diagnostics._0_is_declared_but_its_value_is_never_read, name));
                     }
                 }
             }
         }
+        function isTypeParameterUnused(typeParameter: TypeParameterDeclaration): boolean {
+            return !(getMergedSymbol(typeParameter.symbol).isReferenced! & SymbolFlags.TypeParameter) && !isIdentifierThatStartsWithUnderscore(typeParameter.name);
+        }
 
         function addToGroup<K, V>(map: Map<[K, V[]]>, key: K, value: V, getKey: (key: K) => number | string): void {
             const keyString = String(getKey(key));

src/compiler/core.ts

@@ -2093,7 +2093,7 @@ namespace ts {
         return arg => f(arg) || g(arg);
     }
 
-    export function assertTypeIsNever(_: never): void { } // tslint:disable-line no-empty
+    export function assertType<T>(_: T): void { } // tslint:disable-line no-empty
 
     export function singleElementArray<T>(t: T | undefined): T[] | undefined {
         return t === undefined ? undefined : [t];

src/compiler/diagnosticMessages.json

@@ -3655,6 +3655,10 @@
         "category": "Message",
         "code": 6204
     },
+    "All type parameters are unused": {
+        "category": "Error",
+        "code": 6205
+    },
 
     "Projects to reference": {
         "category": "Message",
@@ -4208,6 +4212,14 @@
         "category": "Message",
         "code": 90010
     },
+    "Remove template tag": {
+        "category": "Message",
+        "code": 90011
+    },
+    "Remove type parameters": {
+        "category": "Message",
+        "code": 90012
+    },
     "Import '{0}' from module \"{1}\"": {
         "category": "Message",
         "code": 90013
@@ -4276,6 +4288,14 @@
         "category": "Message",
         "code": 90029
     },
+    "Replace 'infer {0}' with 'unknown'": {
+        "category": "Message",
+        "code": 90030
+    },
+    "Replace all unused 'infer' with 'unknown'": {
+        "category": "Message",
+        "code": 90031
+    },
     "Convert function to an ES2015 class": {
         "category": "Message",
         "code": 95001

src/compiler/parser.ts

@@ -7030,8 +7030,8 @@ namespace ts {
                         skipWhitespace();
                         const typeParameter = <TypeParameterDeclaration>createNode(SyntaxKind.TypeParameter);
                         typeParameter.name = parseJSDocIdentifierName(Diagnostics.Unexpected_token_A_type_parameter_name_was_expected_without_curly_braces);
-                        skipWhitespace();
                         finishNode(typeParameter);
+                        skipWhitespace();
                         typeParameters.push(typeParameter);
                     } while (parseOptionalJsdoc(SyntaxKind.CommaToken));
 

src/compiler/tsbuild.ts

@@ -1268,7 +1268,7 @@ namespace ts {
                 // Don't report status on "solution" projects
                 break;
             default:
-                assertTypeIsNever(status);
+                assertType<never>(status);
         }
     }
 }

src/compiler/utilities.ts

@@ -676,6 +676,19 @@ namespace ts {
 
     export function isDeclarationWithTypeParameters(node: Node): node is DeclarationWithTypeParameters;
     export function isDeclarationWithTypeParameters(node: DeclarationWithTypeParameters): node is DeclarationWithTypeParameters {
+        switch (node.kind) {
+            case SyntaxKind.JSDocCallbackTag:
+            case SyntaxKind.JSDocTypedefTag:
+            case SyntaxKind.JSDocSignature:
+                return true;
+            default:
+                assertType<DeclarationWithTypeParameterChildren>(node);
+                return isDeclarationWithTypeParameterChildren(node);
+        }
+    }
+
+    export function isDeclarationWithTypeParameterChildren(node: Node): node is DeclarationWithTypeParameterChildren;
+    export function isDeclarationWithTypeParameterChildren(node: DeclarationWithTypeParameterChildren): node is DeclarationWithTypeParameterChildren {
         switch (node.kind) {
             case SyntaxKind.CallSignature:
             case SyntaxKind.ConstructSignature:
@@ -696,12 +709,9 @@ namespace ts {
             case SyntaxKind.SetAccessor:
             case SyntaxKind.FunctionExpression:
             case SyntaxKind.ArrowFunction:
-            case SyntaxKind.JSDocCallbackTag:
-            case SyntaxKind.JSDocTypedefTag:
-            case SyntaxKind.JSDocSignature:
                 return true;
             default:
-                assertTypeIsNever(node);
+                assertType<never>(node);
                 return false;
         }
     }
@@ -786,7 +796,7 @@ namespace ts {
         return createDiagnosticForNodeInSourceFile(sourceFile, node, message, arg0, arg1, arg2, arg3);
     }
 
-    export function createDiagnosticForNodeArray(sourceFile: SourceFile, nodes: NodeArray<Node>, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): Diagnostic {
+    export function createDiagnosticForNodeArray(sourceFile: SourceFile, nodes: NodeArray<Node>, message: DiagnosticMessage, arg0?: string | number, arg1?: string | number, arg2?: string | number, arg3?: string | number): DiagnosticWithLocation {
         const start = skipTrivia(sourceFile.text, nodes.pos);
         return createFileDiagnostic(sourceFile, start, nodes.end - start, message, arg0, arg1, arg2, arg3);
     }
@@ -8128,4 +8138,75 @@ namespace ts {
         }
         return { min, max };
     }
+
+    export interface ReadonlyNodeSet<TNode extends Node> {
+        has(node: TNode): boolean;
+        forEach(cb: (node: TNode) => void): void;
+        some(pred: (node: TNode) => boolean): boolean;
+    }
+
+    export class NodeSet<TNode extends Node> implements ReadonlyNodeSet<TNode> {
+        private map = createMap<TNode>();
+
+        add(node: TNode): void {
+            this.map.set(String(getNodeId(node)), node);
+        }
+        tryAdd(node: TNode): boolean {
+            if (this.has(node)) return false;
+            this.add(node);
+            return true;
+        }
+        has(node: TNode): boolean {
+            return this.map.has(String(getNodeId(node)));
+        }
+        forEach(cb: (node: TNode) => void): void {
+            this.map.forEach(cb);
+        }
+        some(pred: (node: TNode) => boolean): boolean {
+            return forEachEntry(this.map, pred) || false;
+        }
+    }
+
+    export interface ReadonlyNodeMap<TNode extends Node, TValue> {
+        get(node: TNode): TValue | undefined;
+        has(node: TNode): boolean;
+    }
+
+    export class NodeMap<TNode extends Node, TValue> implements ReadonlyNodeMap<TNode, TValue> {
+        private map = createMap<{ node: TNode, value: TValue }>();
+
+        get(node: TNode): TValue | undefined {
+            const res = this.map.get(String(getNodeId(node)));
+            return res && res.value;
+        }
+
+        getOrUpdate(node: TNode, setValue: () => TValue): TValue {
+            const res = this.get(node);
+            if (res) return res;
+            const value = setValue();
+            this.set(node, value);
+            return value;
+        }
+
+        set(node: TNode, value: TValue): void {
+            this.map.set(String(getNodeId(node)), { node, value });
+        }
+
+        has(node: TNode): boolean {
+            return this.map.has(String(getNodeId(node)));
+        }
+
+        forEach(cb: (value: TValue, node: TNode) => void): void {
+            this.map.forEach(({ node, value }) => cb(value, node));
+        }
+    }
+
+    export function rangeOfNode(node: Node): TextRange {
+        return { pos: getTokenPosOfNode(node), end: node.end };
+    }
+
+    export function rangeOfTypeParameters(typeParameters: NodeArray<TypeParameterDeclaration>): TextRange {
+        // Include the `<>`
+        return { pos: typeParameters.pos - 1, end: typeParameters.end + 1 };
+    }
 }