fix(eslint-plugin): [no-unnec-type-arg] undefined symbol crash (typescript-eslint#1007)

quentin-jaquier-sonarsource · bradzacher · commit cdf92949bec4 · 2019-09-24T08:46:00.000-07:00
diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-arguments.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-arguments.ts
@@ -121,7 +121,12 @@ function getTypeParametersFromType(
   type: ts.EntityName | ts.Expression | ts.ClassDeclaration,
   checker: ts.TypeChecker,
 ): readonly ts.TypeParameterDeclaration[] | undefined {
-  const sym = getAliasedSymbol(checker.getSymbolAtLocation(type)!, checker);
+  const symAtLocation = checker.getSymbolAtLocation(type);
+  if (symAtLocation === undefined) {
+    return undefined;
+  }
+
+  const sym = getAliasedSymbol(symAtLocation, checker);
   if (sym === undefined || sym.declarations === undefined) {
     return undefined;
   }
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-arguments.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-arguments.test.ts
@@ -52,6 +52,7 @@ ruleTester.run('no-unnecessary-type-arguments', rule, {
       class D<TD = number> extends C { }`,
     `declare const C: unknown;
       class D<TD = number> extends C { }`,
+    `let a: A<number>`,
   ],
   invalid: [
     {

Original file line number	Diff line number	Diff line change
`@@ -52,6 +52,7 @@ ruleTester.run('no-unnecessary-type-arguments', rule, {`
`52`	`52`	class D<TD = number> extends C { }`,
`53`	`53`	`declare const C: unknown;
`54`	`54`	class D<TD = number> extends C { }`,
	`55`	+ `let a: A<number>`,
`55`	`56`	`],`
`56`	`57`	`invalid: [`
`57`	`58`	`{`