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chore: add errors and type assertions to sass-ext
PiperOrigin-RevId: 826549583
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‎sass/ext/_assert.scss‎

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//
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// Copyright 2025 Google LLC
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// SPDX-License-Identifier: Apache-2.0
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//
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// Utility assert functions that throw errors.
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// go/keep-sorted start by_regex='(.+) prefix_order=sass:
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@use 'sass:meta';
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@use 'throw';
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@use 'type';
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// go/keep-sorted end
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/// Asserts that the argument is a specific type. If it is, the argument is
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/// returned, otherwise an error is thrown.
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///
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/// @example scss
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/// @mixin multiply($a, $b) {
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/// $a: assert.is-type($a, 'number');
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/// $b: assert.is-type($b, 'number');
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/// @return $a * $b;
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/// }
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///
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/// @function is-empty($value) {
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/// $value: assert.is-type(
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/// $value,
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/// 'list|map|null',
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/// $message: '$value must be a list, map, or null',
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/// $source: 'is-empty'
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/// );
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/// @return $value and list.length($value) == 0;
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/// }
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///
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/// @param {*} $arg - The argument to check.
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/// @param {string} $type - The string type to assert the argument matches.
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/// Multiple types may be separated by '|'.
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/// @param {string} $message - Optional custom error message.
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/// @param {string} $source - Optional source of the error message.
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/// @return {*} The argument if it matches the type string.
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/// @throw Error if the argument does not match the type string.
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@function is-type(
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$arg,
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$type,
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$message: 'Argument must be type #{meta.inspect($type)}. $arg: #{meta.inspect($arg)}',
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$source: 'assert.is-type'
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) {
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@if type.matches($arg, $type) {
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@return $arg;
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}
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@return throw.error($message, $source);
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}
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/// Asserts that the argument is a specific type. If it is, the argument is
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/// returned, otherwise an error is thrown.
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///
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/// @example scss
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/// @function get-or-throw($map, $key) {
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/// @return assert.not-type(
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/// map.get($map, $key),
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/// 'null',
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/// $message: 'Key must be in the map'
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/// );
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/// }
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///
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/// @param {*} $arg - The argument to check.
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/// @param {string} $type - The string type to assert the argument does not
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/// match. Multiple types may be separated by '|'.
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/// @param {string} $message - Optional custom error message.
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/// @param {string} $source - Optional source of the error message.
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/// @return {*} The argument if it does not match the type string.
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/// @throw Error if the argument matches the type string.
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@function not-type(
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$arg,
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$type,
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$message: 'Argument may not be type #{meta.inspect($type)}. $arg: #{meta.inspect($arg)}',
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$source: 'assert.not-type'
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) {
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@if type.matches($arg, $type) {
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@return throw.error($message, $source);
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}
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@return $arg;
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}

‎sass/ext/_assert_test.scss‎

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//
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// Copyright 2025 Google LLC
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// SPDX-License-Identifier: Apache-2.0
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//
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@use 'true' as test;
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// go/keep-sorted start by_regex='(.+) prefix_order=sass:
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@use 'sass:string';
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@use 'assert';
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@use 'throw';
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// go/keep-sorted end
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@include test.describe('assert') {
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// Value types
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$number: 1;
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$string: 'a-string';
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$color: red;
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$bool: true;
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$null: null;
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$list: ('list', 'of', 'values');
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$map: (
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'map': 'value',
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);
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@include test.describe('is-type()') {
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@include test.it('returns the argument when it matches a single type') {
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@include test.assert-equal(assert.is-type($number, 'number'), $number);
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@include test.assert-equal(assert.is-type($string, 'string'), $string);
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@include test.assert-equal(assert.is-type($bool, 'bool'), $bool);
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@include test.assert-equal(assert.is-type($null, 'null'), $null);
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@include test.assert-equal(assert.is-type($list, 'list'), $list);
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@include test.assert-equal(assert.is-type($map, 'map'), $map);
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}
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@include test.it(
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'returns the argument when it matches one of multiple types'
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) {
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@include test.assert-equal(
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assert.is-type($number, 'number|string'),
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$number
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);
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@include test.assert-equal(
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assert.is-type($string, 'number|string'),
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$string
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);
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@include test.assert-equal(assert.is-type($null, 'list|map|null'), $null);
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@include test.assert-equal(assert.is-type($list, 'list|map|null'), $list);
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@include test.assert-equal(assert.is-type($map, 'list|map|null'), $map);
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}
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@include test.it('throws an error when it does not match the type') {
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@include test.assert-true(
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throw.get-error(assert.is-type($number, 'string')),
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'number should not match "string" type'
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);
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@include test.assert-true(
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throw.get-error(assert.is-type($string, 'number')),
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'string should not match "number" type'
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);
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@include test.assert-true(
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throw.get-error(assert.is-type($null, 'list|map')),
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'null should not match "list|map" type'
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);
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}
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}
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@include test.describe('not-type()') {
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@include test.it(
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'returns the argument when it does not match a single type'
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) {
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@include test.assert-equal(assert.not-type($number, 'string'), $number);
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@include test.assert-equal(assert.not-type($string, 'number'), $string);
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@include test.assert-equal(assert.not-type($bool, 'string'), $bool);
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@include test.assert-equal(assert.not-type($null, 'string'), $null);
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@include test.assert-equal(assert.not-type($list, 'string'), $list);
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@include test.assert-equal(assert.not-type($map, 'string'), $map);
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}
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@include test.it(
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'returns the argument when it does not match one of multiple types'
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) {
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@include test.assert-equal(
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assert.not-type($number, 'string|map'),
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$number
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);
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@include test.assert-equal(
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assert.not-type($string, 'number|map'),
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$string
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);
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@include test.assert-equal(assert.not-type($null, 'list|map'), $null);
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}
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@include test.it('throws an error when it matches the type') {
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@include test.assert-true(
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throw.get-error(assert.not-type($number, 'number')),
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'number should match "number" type and throw'
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);
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@include test.assert-true(
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throw.get-error(assert.not-type($string, 'string')),
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'string should match "string" type and throw'
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);
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@include test.assert-true(
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throw.get-error(assert.not-type($null, 'null')),
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'null should match "null" type and throw'
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);
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@include test.assert-true(
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throw.get-error(assert.not-type($number, 'number|string')),
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'number should match "number|string" type and throw'
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);
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@include test.assert-true(
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throw.get-error(assert.not-type($string, 'number|string')),
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'string should match "number|string" type and throw'
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);
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@include test.assert-true(
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throw.get-error(assert.not-type($null, 'list|map|null')),
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'null should match "list|map|null" type and throw'
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);
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}
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}
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}

‎sass/ext/_throw.scss‎

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//
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// Copyright 2025 Google LLC
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// SPDX-License-Identifier: Apache-2.0
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//
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// Utilities for `sass-true` errors, to support testing error behavior.
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// go/keep-sorted start by_regex='(.+) prefix_order=sass:
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@use 'sass:meta';
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@use 'sass:string';
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// go/keep-sorted end
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@forward 'true' show error;
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/// Returns false if none of the given values are error strings, or returns an
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/// error string if any value has an error.
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///
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/// This is used to support testing error behavior with `sass-true`, since
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/// `@error` messages cannot be caught at build time.
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///
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/// @example scss
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/// // A function that may return an "ERROR:" string in a test.
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/// @function get-value($map, $key) {
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/// @if meta.type-of($map) != 'map' {
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/// // Identical to `@error 'ERROR: Arg is not a map'` outside of tests.
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/// @return throw.error('Arg is not a map');
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/// }
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/// @return map.get($map, $key);
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/// }
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///
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/// // A function that needs to handle potential errors from other functions.
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/// @function mix-primary-on-surface($values) {
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/// $primary: get-value($values, 'primary');
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/// $surface: get-value($values, 'surface');
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/// $error: throw.get-error($primary, $secondary);
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/// @if $error {
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/// // Return early to guard logic against additional errors since
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/// // $primary or $secondary may be a string instead of a color.
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/// @return $error;
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/// }
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///
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/// @return color.mix($primary, $surface, 10%);
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/// }
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///
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/// Note: `throw.error()` and `throw.get-error()` are only useful when testing
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/// error behavior using `sass-true`. If you are not testing a function, use
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/// `@error` instead.
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///
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/// @example scss
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/// // In a `sass-true` test, `throw.get-error()` can be used to assert that
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/// // an error is thrown.
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/// @use 'true' as test with ($catch-errors: true);
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///
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/// @include test.describe('module.get-value()') {
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/// @include test.it('throws an error if the value is not a map') {
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/// $result: module.get-value('not a map', 'primary');
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/// @include test.assert-truthy(throw.get-error($result), '$result is an error');
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/// }
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/// }
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///
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/// @param {*} $error - The value to check.
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/// @param {list} $errors - Additional values to check. Useful for checking
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/// multiple errors at the same time.
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/// @return {string|boolean} The error string if any value is an error, or false
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/// otherwise.
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@function get-error($error, $errors...) {
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@if _is-error($error) {
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@return $error;
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}
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@each $additional-error in $errors {
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@if _is-error($additional-error) {
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@return $additional-error;
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}
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}
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@return false;
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}
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@function _is-error($error) {
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@return (meta.type-of($error) == 'string') and
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(string.index($error, 'ERROR') == 1);
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}

‎sass/ext/_throw_test.scss‎

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//
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// Copyright 2025 Google LLC
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// SPDX-License-Identifier: Apache-2.0
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//
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@use 'true' as test;
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// go/keep-sorted start by_regex='(.+) prefix_order=sass:
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@use 'throw';
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// go/keep-sorted end
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@include test.describe('throw') {
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@include test.describe('get-error()') {
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@include test.it('returns the string if the value is an error string') {
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$error: throw.error('test error message');
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@include test.assert-equal(throw.get-error($error), $error);
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}
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@include test.it('returns null for non-error strings') {
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@include test.assert-false(
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throw.get-error('not an error'),
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'get-error("not an error") should return null for non-error strings'
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);
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}
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@include test.it('returns null for other values') {
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@include test.assert-false(
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throw.get-error(1),
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'get-error(1) should return null'
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);
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@include test.assert-false(
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throw.get-error(true),
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'get-error(true) should return null'
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);
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@include test.assert-false(
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throw.get-error(null),
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'get-error(null) should return null'
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);
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@include test.assert-false(
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throw.get-error(()),
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'get-error(()) should return null'
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);
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}
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@include test.it(
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'returns the first error if multiple values are provided'
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) {
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$error: throw.error('test error message');
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@include test.assert-equal(
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throw.get-error(
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'not an error',
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'still not an error',
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$error,
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'not an error either'
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),
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$error
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);
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}
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@include test.it('returns null if multiple non-error values are provided') {
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@include test.assert-false(
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throw.get-error('not an error', 'still not an error'),
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'get-error("not an error", "still not an error") should return null'
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);
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}
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}
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}

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