Determine which config files each sheet uses

packages/@tailwindcss-upgrade/src/migrate.ts

@@ -125,6 +125,24 @@ export async function analyze(stylesheets: Stylesheet[]) {
       }
     }
   }
+
+  // Step 3: Determine which config files are used by each stylesheet (if any)
+  for (let sheet of stylesheets) {
+    for (let node of sheet.configRules) {
+      let configPath = node.params.match(/['"](.*)['"]/)?.[1]
+      if (!configPath) continue
+
+      sheet.configFiles.add(configPath)
+    }
+  }
+
+  for (let sheet of stylesheets) {
+    for (let parent of sheet.ancestors) {
+      for (let file of parent.configFiles) {
+        sheet.configFiles.add(file)
+      }
+    }
+  }
 }
 
 export async function split(stylesheets: Stylesheet[]) {

packages/@tailwindcss-upgrade/src/stylesheet.ts

@@ -40,6 +40,11 @@ export class Stylesheet {
    */
   layers = new Set<string>()
 
+  /**
+   * The list of config files that this stylesheet uses
+   */
+  configFiles = new Set<string>()
+
   static async load(filepath: string) {
     filepath = path.resolve(process.cwd(), filepath)
 
@@ -75,6 +80,16 @@ export class Stylesheet {
     return imports
   }
 
+  get configRules() {
+    let rules = new Set<postcss.AtRule>()
+
+    this.root.walkAtRules('config', (rule) => {
+      rules.add(rule)
+    })
+
+    return rules
+  }
+
   get isEmpty() {
     return this.root.toString().trim() === ''
   }