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no-unnecessary-generics.ts
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no-unnecessary-generics.ts
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import { ESLintUtils, TSESTree } from "@typescript-eslint/utils";
import * as ts from "typescript";
import { createRule } from "../util";
type ESTreeFunctionLikeWithTypeParameters = TSESTree.FunctionLike & {
typeParameters: {};
};
type TSSignatureDeclarationWithTypeParameters = ts.SignatureDeclaration & {
typeParameters: {};
};
const rule = createRule({
defaultOptions: [],
meta: {
docs: {
description: "Forbids signatures using a generic parameter only once.",
recommended: "error",
},
messages: {
never: "Type parameter {{name}} is never used.",
sole: "Type parameter {{name}} is used only once.",
},
schema: [],
type: "problem",
},
name: "no-relative-import-in-test",
create(context) {
return {
[[
"ArrowFunctionExpression[typeParameters]",
"FunctionDeclaration[typeParameters]",
"FunctionExpression[typeParameters]",
"TSCallSignatureDeclaration[typeParameters]",
"TSConstructorType[typeParameters]",
"TSDeclareFunction[typeParameters]",
"TSFunctionType[typeParameters]",
"TSMethodSignature[typeParameters]",
].join(", ")](esNode: ESTreeFunctionLikeWithTypeParameters) {
const parserServices = ESLintUtils.getParserServices(context);
const tsNode = parserServices.esTreeNodeToTSNodeMap.get(esNode) as TSSignatureDeclarationWithTypeParameters;
if (!tsNode.typeParameters) {
return;
}
const checker = parserServices.program.getTypeChecker();
for (const typeParameter of tsNode.typeParameters) {
const name = typeParameter.name.text;
const res = getSoleUse(tsNode, assertDefined(checker.getSymbolAtLocation(typeParameter.name)), checker);
switch (res.type) {
case "sole":
context.report({
data: { name },
messageId: "sole",
node: parserServices.tsNodeToESTreeNodeMap.get(res.soleUse),
});
break;
case "never":
context.report({
data: { name },
messageId: "never",
node: parserServices.tsNodeToESTreeNodeMap.get(typeParameter),
});
break;
}
}
},
};
},
});
type Result = { type: "ok" | "never" } | { type: "sole"; soleUse: ts.Identifier };
function getSoleUse(sig: ts.SignatureDeclaration, typeParameterSymbol: ts.Symbol, checker: ts.TypeChecker): Result {
const exit = {};
let soleUse: ts.Identifier | undefined;
try {
if (sig.typeParameters) {
for (const tp of sig.typeParameters) {
if (tp.constraint) {
recurse(tp.constraint);
}
}
}
for (const param of sig.parameters) {
if (param.type) {
recurse(param.type);
}
}
if (sig.type) {
recurse(sig.type);
}
} catch (err) {
if (err === exit) {
return { type: "ok" };
}
throw err;
}
return soleUse ? { type: "sole", soleUse } : { type: "never" };
function recurse(node: ts.Node): void {
if (ts.isIdentifier(node)) {
if (checker.getSymbolAtLocation(node) === typeParameterSymbol) {
if (soleUse === undefined) {
soleUse = node;
} else {
throw exit;
}
}
} else {
node.forEachChild(recurse);
}
}
}
export = rule;
function assertDefined<T>(value: T | undefined): T {
if (value === undefined) {
throw new Error("unreachable");
}
return value;
}