Attempt to detect installed Sass implementation

CHANGELOG.md

@@ -1,5 +1,13 @@
 # True Changelog
 
+## Unreleased
+
+- FEATURE: If True `sass` option is not specified, True will automatically
+  attempt to use `embedded-sass`, then `sass`.
+  [#290](https://github.com/oddbird/true/issues/290)
+- INTERNAL: Add `sass` and `sass-embedded` as optional peer-dependencies.
+- INTERNAL: Update dependencies
+
 ## 8.0.0 (02/23/24)
 
 - FEATURE: Add True `sass` option (`string` or Sass implementation instance,

README.md

@@ -31,6 +31,12 @@ In command line:
 npm install --save-dev sass-true
 ```
 
+True requires Dart Sass v1.45.0 or higher, so install it if you haven't already:
+
+```bash
+npm install --save-dev sass-embedded # or `sass`
+```
+
 Import in your test directory,
 like any other Sass file:
 
@@ -155,11 +161,11 @@ when upgrading from an older version of True.
    npm install --save-dev sass-true
    ```
 
-2. [Optional] Install Dart Sass (`sass` or `sass-embedded`), if not already
+2. [Optional] Install Dart Sass (`sass-embedded` or `sass`), if not already
    installed.
 
    ```bash
-   npm install --save-dev sass
+   npm install --save-dev sass-embedded # or `sass`
    ```
 
 3. Write some Sass tests in `test/test.scss` (see above).
@@ -203,8 +209,8 @@ should be usable in the same way: just pass your test runner's `describe` and
 
 The `sass` option is an optional string name of a Dart Sass implementation
 installed in the current environment (e.g. `'embedded-sass'` or `'sass'`), or a
-Dart Sass implementation instance itself. If none is provided, this defaults to
-`'sass'`.
+Dart Sass implementation instance itself. If none is provided, True will attempt
+to detect which implementation is available, starting with `sass-embedded`.
 
 If True can't parse the CSS output, it'll give you some context lines of CSS as
 part of the error message. This context will likely be helpful in understanding

package.json

@@ -66,6 +66,18 @@
     "jest-diff": "^29.7.0",
     "lodash": "^4.17.21"
   },
+  "peerDependencies": {
+    "sass": ">=1.45.0",
+    "sass-embedded": ">=1.45.0"
+  },
+  "peerDependenciesMeta": {
+    "sass": {
+      "optional": true
+    },
+    "sass-embedded": {
+      "optional": true
+    }
+  },
   "devDependencies": {
     "@babel/core": "^7.25.2",
     "@babel/preset-env": "^7.25.4",

src/index.ts

@@ -66,6 +66,16 @@ export type Rule = CssCommentAST | CssRuleAST | CssAtRuleAST;
 
 export type Parser = (rule: Rule, ctx: Context) => Parser;
 
+const loadSass = function (sassPkg: string) {
+  try {
+    // eslint-disable-next-line global-require
+    return require(sassPkg);
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+  } catch (err) {
+    throw new Error(`Cannot find Dart Sass (\`${sassPkg}\`) dependency.`);
+  }
+};
+
 export const runSass = function (
   trueOptions: TrueOptions,
   src: string,
@@ -103,14 +113,23 @@ export const runSass = function (
   let compiler;
   if (trueOpts.sass && typeof trueOpts.sass !== 'string') {
     compiler = trueOpts.sass;
+  } else if (typeof trueOpts.sass === 'string') {
+    compiler = loadSass(trueOpts.sass);
   } else {
-    const sassPkg = trueOpts.sass ?? 'sass';
     try {
-      // eslint-disable-next-line global-require
-      compiler = require(sassPkg);
+      // try sass-embedded before sass
+      compiler = loadSass('sass-embedded');
       // eslint-disable-next-line @typescript-eslint/no-unused-vars
-    } catch (err) {
-      throw new Error(`Cannot find Dart Sass (\`${sassPkg}\`) dependency.`);
+    } catch (e1) {
+      /* istanbul ignore next */
+      try {
+        compiler = loadSass('sass');
+        // eslint-disable-next-line @typescript-eslint/no-unused-vars
+      } catch (e2) {
+        throw new Error(
+          'Cannot find Dart Sass (`sass-embedded` or `sass`) dependency.',
+        );
+      }
     }
   }