Apr 24, 2019 · Apr 19, 2019 · Apr 24, 2019
diff --git a/packages/eslint-plugin/src/rules/restrict-plus-operands.ts b/packages/eslint-plugin/src/rules/restrict-plus-operands.ts
    docs: {
      description:
        'When adding two variables, operands must both be of type number or of type string.',
 tslintRuleName: 'restrict-plus-operands',
 tslintName: 'restrict-plus-operands',
      category: 'Best Practices',
      recommended: false,
    },

    /**
     * Helper function to get base type of node
     * @param type type to be evaluated
     * @returns string, number or invalid
     */
    function getBaseTypeOfLiteralType(type: ts.Type): BaseLiteral {
      const constraint = type.getConstraint();
      if (
        constraint &&
        // for generic types with union constraints, it will return itself from getConstraint
        // so we have to guard against infinite recursion...
        constraint !== type
      ) {
        return getBaseTypeOfLiteralType(constraint);
      }

      if (type.isNumberLiteral()) {
        return 'number';
      }
diff --git a/packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts b/packages/eslint-plugin/tests/rules/restrict-plus-operands.test.ts
    `const foo = 'hello' + (someBoolean ? 'a' : 'b') + (() => someBoolean ? 'c' : 'd')() + 'e';`,
    `const balls = true;`,
    `balls === true;`,
    // https://github.com/typescript-eslint/typescript-eslint/issues/230
    `
 function foo<T extends string>(a: T) {
    return a + "";
 }
    `,
    `
 function foo<T extends "a" | "b">(a: T) {
    return a + "";
 }
    `,
    `
 function foo<T extends number>(a: T) {
    return a + 1;
 }
    `,
    `
 function foo<T extends 1>(a: T) {
    return a + 1;
 }
    `,
  ],
  invalid: [
    {
        },
      ],
    },
    // https://github.com/typescript-eslint/typescript-eslint/issues/230
    {
      code: `
 function foo<T extends string>(a: T) {
    return a + 1;
 }
      `,
      errors: [
        {
          messageId: 'notStrings',
          line: 3,
          column: 12,
        },
      ],
    },
    {
      code: `
 function foo<T extends "a" | "b">(a: T) {
    return a + 1;
 }
      `,
      errors: [
        {
          messageId: 'notStrings',
          line: 3,
          column: 12,
        },
      ],
    },
    {
      code: `
 function foo<T extends number>(a: T) {
    return a + "";
 }
      `,
      errors: [
        {
          messageId: 'notStrings',
          line: 3,
          column: 12,
        },
      ],
    },
    {
      code: `
 function foo<T extends 1>(a: T) {
    return a + "";
 }
      `,
      errors: [
        {
          messageId: 'notStrings',
          line: 3,
          column: 12,
        },
      ],
    },
  ],
 });
Original file line number	Diff line number	Diff line change
Expand Up		@@ -9,7 +9,7 @@ export default util.createRule({
		docs: {
		description:
		'When adding two variables, operands must both be of type number or of type string.',
		tslintRuleName: 'restrict-plus-operands',
		tslintName: 'restrict-plus-operands',
		category: 'Best Practices',
		recommended: false,
		},
Expand All		@@ -32,10 +32,18 @@ export default util.createRule({

		/**
		* Helper function to get base type of node
		* @param type type to be evaluated
		* @returns string, number or invalid
		*/
		function getBaseTypeOfLiteralType(type: ts.Type): BaseLiteral {
		const constraint = type.getConstraint();
		if (
		constraint &&
		// for generic types with union constraints, it will return itself from getConstraint
		// so we have to guard against infinite recursion...
		constraint !== type
		) {
		return getBaseTypeOfLiteralType(constraint);
		}

		if (type.isNumberLiteral()) {
		return 'number';
		}
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -60,6 +60,27 @@ var foo = ("5.5" as string) + pair.second;
		`const foo = 'hello' + (someBoolean ? 'a' : 'b') + (() => someBoolean ? 'c' : 'd')() + 'e';`,
		`const balls = true;`,
		`balls === true;`,
		// https://github.com/typescript-eslint/typescript-eslint/issues/230
		`
		function foo<T extends string>(a: T) {
		return a + "";
		}
		`,
		`
		function foo<T extends "a" \| "b">(a: T) {
		return a + "";
		}
		`,
		`
		function foo<T extends number>(a: T) {
		return a + 1;
		}
		`,
		`
		function foo<T extends 1>(a: T) {
		return a + 1;
		}
		`,
		],
		invalid: [
		{
Expand DownExpand Up		@@ -305,5 +326,62 @@ var foo = pair + pair;
		},
		],
		},
		// https://github.com/typescript-eslint/typescript-eslint/issues/230
		{
		code: `
		function foo<T extends string>(a: T) {
		return a + 1;
		}
		`,
		errors: [
		{
		messageId: 'notStrings',
		line: 3,
		column: 12,
		},
		],
		},
		{
		code: `
		function foo<T extends "a" \| "b">(a: T) {
		return a + 1;
		}
		`,
		errors: [
		{
		messageId: 'notStrings',
		line: 3,
		column: 12,
		},
		],
		},
		{
		code: `
		function foo<T extends number>(a: T) {
		return a + "";
		}
		`,
		errors: [
		{
		messageId: 'notStrings',
		line: 3,
		column: 12,
		},
		],
		},
		{
		code: `
		function foo<T extends 1>(a: T) {
		return a + "";
		}
		`,
		errors: [
		{
		messageId: 'notStrings',
		line: 3,
		column: 12,
		},
		],
		},
		],
		});