[eas-cli] Fix flavor detection when build.gradle uses string interpolation

CHANGELOG.md

@@ -10,6 +10,8 @@ This is the log of notable changes to EAS CLI and related packages.
 
 ### 🐛 Bug fixes
 
+- [eas-cli] Fix flavor detection in `build.gradle` files that use string interpolation, such as `buildConfigField "String", "KEY", "\"${System.getenv("KEY")}\""`, which made `eas build` fail with "Failed to autodetect applicationId in multi-flavor project". ([#4260](https://github.com/expo/eas-cli/pull/4260) by [@giaBaoJS](https://github.com/giaBaoJS))
+
 ### 🧹 Chores
 
 ## [23.2.0](https://github.com/expo/eas-cli/releases/tag/v23.2.0) - 2026-08-31

packages/eas-cli/src/project/android/__tests__/fixtures/string-interpolation-in-build.gradle

@@ -0,0 +1,62 @@
+apply plugin: "com.android.application"
+
+import com.android.build.OutputFile
+
+def enableProguardInReleaseBuilds = false
+def jscFlavor = 'org.webkit:android-jsc:+'
+
+android {
+    compileSdkVersion rootProject.ext.compileSdkVersion
+
+    buildFeatures {
+        buildConfig true
+    }
+
+    defaultConfig {
+        applicationId "com.testapp"
+        minSdkVersion rootProject.ext.minSdkVersion
+        targetSdkVersion rootProject.ext.targetSdkVersion
+        versionCode 1
+        versionName "1.0"
+
+        buildConfigField "String", "API_KEY", "\"${System.getenv("API_KEY")}\""
+        buildConfigField "String", "BUILD_LABEL", "\"${System.getenv("FLAVOR")}-${System.getenv("STAGE")}\""
+        resValue "string", "app_id", "\"${System.getenv("APP_ID")}\""
+    }
+    flavorDimensions "env"
+    productFlavors {
+        staging {
+            dimension "env"
+            applicationId "com.testapp.staging"
+            versionCode 123
+        }
+        production {
+            dimension "env"
+            applicationId "com.testapp"
+            versionCode 124
+        }
+    }
+    buildTypes {
+        release {
+            minifyEnabled enableProguardInReleaseBuilds
+            proguardFiles getDefaultProguardFile("proguard-android.txt"), "proguard-rules.pro"
+        }
+    }
+
+    applicationVariants.all { variant ->
+        variant.outputs.each { output ->
+            def abi = output.getFilter(OutputFile.ABI)
+            if (abi != null) {
+                output.versionCodeOverride = defaultConfig.versionCode
+            }
+        }
+    }
+}
+
+dependencies {
+    implementation "com.facebook.react:react-native:+"
+    debugImplementation("com.facebook.flipper:flipper:${FLIPPER_VERSION}") {
+      exclude group:'com.facebook.fbjni'
+    }
+    implementation jscFlavor
+}

packages/eas-cli/src/project/android/__tests__/gradleUtils-test.ts

@@ -166,6 +166,35 @@ describe(getAppBuildGradleAsync, () => {
       },
     });
   });
+
+  test('parsing build.gradle with interpolated strings', async () => {
+    vol.fromJSON(
+      {
+        'android/app/build.gradle': await fsReal.promises.readFile(
+          path.join(__dirname, 'fixtures/string-interpolation-in-build.gradle'),
+          'utf-8'
+        ),
+      },
+      '/test'
+    );
+    const buildGradle = await getAppBuildGradleAsync('/test');
+    expect(pick(buildGradle?.android ?? {}, ['flavorDimensions', 'productFlavors'])).toEqual({
+      flavorDimensions: 'env',
+      productFlavors: {
+        staging: {
+          applicationId: 'com.testapp.staging',
+          versionCode: '123',
+          dimension: 'env',
+        },
+        production: {
+          applicationId: 'com.testapp',
+          versionCode: '124',
+          dimension: 'env',
+        },
+      },
+    });
+    expect(buildGradle?.android?.defaultConfig?.applicationId).toBe('com.testapp');
+  });
 });
 
 describe(parseGradleCommand, () => {

packages/eas-cli/src/project/android/gradleUtils.ts

@@ -45,7 +45,28 @@ export async function getAppBuildGradleAsync(projectDir: string): Promise<AppBui
     .filter(line => !line.trim().startsWith('//'))
     .join('\n');
 
-  return await g2js.parseText(rawBuildGradleWithoutComments);
+  return await g2js.parseText(unwrapStringInterpolations(rawBuildGradleWithoutComments));
+}
+
+/**
+ * gradle-to-js counts `{` and `}` without knowing about string literals, so the braces of a
+ * Groovy string interpolation are treated as a block. When the interpolation contains a method
+ * call, like `buildConfigField "String", "KEY", "\"${System.getenv("KEY")}\""`, the parser
+ * skips one character too many and swallows the closing brace of the surrounding block. Every
+ * entry that follows then ends up nested in the wrong place, which is why `android.productFlavors`
+ * comes back as `undefined` for projects that use interpolated build config fields.
+ *
+ * Unwrapping the interpolations drops the braces and keeps their content. `[^{}]*` never matches
+ * across a brace, so nested interpolations are unwrapped one level per pass.
+ */
+function unwrapStringInterpolations(buildGradle: string): string {
+  let result = buildGradle;
+  let previousResult;
+  do {
+    previousResult = result;
+    result = result.replace(/\$\{([^{}]*)\}/g, '$$$1');
+  } while (result !== previousResult);
+  return result;
 }
 
 export function resolveConfigValue(