Fix PostCSS crash when using toJSON() (#18083)

thecrypticace · web-flow · commit 9df5ba78bf1e · 2025-05-19T11:28:09.000-04:00
When I added source maps to PostCSS I mistakenly assumed that `.source` on a node could be `undefined`. The comment above the property in PostCSS says that `source` can be `undefined` but this is a commentary on the value upon **access** not its expected value on **write**: ```ts declare abstract class Node_ { /** * … * * The nodes that are created manually using the public APIs * provided by PostCSS will have `source` undefined and * will be absent in the source map. * * … */ source?: Node.Source } ``` Rather, what these types mean is that *if the property exists* it must be defined. But otherwise the property can be missing if a node has no source location metadata. This generally wasn't a problem with the string-returning APIs but the `toJSON()` API in PostCSS expects that `source` is defined if present. This caused a crash because our license comment doesn't have a source location. I've addressed this by deleting the `source` property from the node if source location data is not available. Fixes #18082 ref parcel-bundler/parcel#10161
diff --git a/packages/@tailwindcss-postcss/src/ast.ts b/packages/@tailwindcss-postcss/src/ast.ts
@@ -49,6 +49,20 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
     }
   }
 
+  function updateSource(astNode: PostCssChildNode, loc: SourceLocation | undefined) {
+    let source = toSource(loc)
+
+    // The `source` property on PostCSS nodes must be defined if present because
+    // `toJSON()` reads each property and tries to read from source.input if it
+    // sees a `source` property. This means for a missing or otherwise absent
+    // source it must be *missing* from the object rather than just `undefined`
+    if (source) {
+      astNode.source = source
+    } else {
+      delete astNode.source
+    }
+  }
+
   function transform(node: AstNode, parent: PostCssContainerNode) {
     // Declaration
     if (node.kind === 'declaration') {
@@ -57,14 +71,14 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
         value: node.value ?? '',
         important: node.important,
       })
-      astNode.source = toSource(node.src)
+      updateSource(astNode, node.src)
       parent.append(astNode)
     }
 
     // Rule
     else if (node.kind === 'rule') {
       let astNode = postcss.rule({ selector: node.selector })
-      astNode.source = toSource(node.src)
+      updateSource(astNode, node.src)
       astNode.raws.semicolon = true
       parent.append(astNode)
       for (let child of node.nodes) {
@@ -75,7 +89,7 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
     // AtRule
     else if (node.kind === 'at-rule') {
       let astNode = postcss.atRule({ name: node.name.slice(1), params: node.params })
-      astNode.source = toSource(node.src)
+      updateSource(astNode, node.src)
       astNode.raws.semicolon = true
       parent.append(astNode)
       for (let child of node.nodes) {
@@ -90,7 +104,7 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
       // spaces.
       astNode.raws.left = ''
       astNode.raws.right = ''
-      astNode.source = toSource(node.src)
+      updateSource(astNode, node.src)
       parent.append(astNode)
     }
 
