Add Android Linting Example

docs/modules/ROOT/nav.adoc

@@ -11,7 +11,6 @@
 ** xref:javalib/publishing.adoc[]
 ** xref:javalib/build-examples.adoc[]
 ** xref:javalib/web-examples.adoc[]
-
 * xref:scalalib/intro.adoc[]
 ** xref:scalalib/module-config.adoc[]
 ** xref:scalalib/dependencies.adoc[]
@@ -31,6 +30,7 @@
 ** xref:kotlinlib/web-examples.adoc[]
 * (Experimental) Android with Mill
 ** xref:android/java.adoc[]
+** xref:android/android-linting.adoc[]
 ** xref:android/kotlin.adoc[]
 * xref:comparisons/why-mill.adoc[]
 ** xref:comparisons/maven.adoc[]

docs/modules/ROOT/pages/android/android-linting.adoc

@@ -0,0 +1,12 @@
+= Linting Android Projects
+:page-aliases: Linting_Android_Projects.adoc
+
+include::partial$gtag-config.adoc[]
+
+This page covers essential practices for maintaining and enforcing code quality
+in Android projects using the Mill build tool. Proper linting helps detect
+and resolve potential issues early, promoting better performance, security,
+and user experience.
+
+
+include::partial$example/android/javalib/3-linting.adoc[]

example/android/javalib/3-linting/app/AndroidManifest.xml

@@ -0,0 +1,12 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.helloworld.app" android:versionCode="1" android:versionName="1.0">
+    <uses-sdk android:minSdkVersion="9" android:targetSdkVersion="35"/>
+    <application android:label="@string/app_name" android:theme="@android:style/Theme.Light.NoTitleBar" android:debuggable="true">
+        <activity android:name=".MainActivity"
+                android:exported="true">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+    </application>
+</manifest>

example/android/javalib/3-linting/app/lint.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<lint>
+    <issue id="MissingApplicationIcon" severity="ignore" />
+</lint>

example/android/javalib/3-linting/app/resources/values/colors.xml

@@ -0,0 +1,4 @@
+<resources>
+    <color name="white">#FFFFFF</color>
+    <color name="text_green">#34A853</color>
+</resources>

example/android/javalib/3-linting/app/resources/values/strings.xml

@@ -0,0 +1,4 @@
+<resources>
+    <string name="app_name">HelloWorldApp</string>
+    <string name="hello_world">Hello, World Java!</string>
+</resources>

example/android/javalib/3-linting/app/src/main/java/com/helloworld/app/MainActivity.java

@@ -0,0 +1,39 @@
+package com.helloworld.app;
+
+import android.app.Activity;
+import android.os.Bundle;
+import android.view.Gravity;
+import android.view.ViewGroup.LayoutParams;
+import android.widget.TextView;
+
+public class MainActivity extends Activity {
+  @Override
+  protected void onCreate(Bundle savedInstanceState) {
+    super.onCreate(savedInstanceState);
+
+    // Create a new TextView
+    TextView textView = new TextView(this);
+
+    // Set the text to the string resource
+    textView.setText(getString(R.string.hello_world));
+
+    // Set text size
+    textView.setTextSize(32);
+
+    // Center the text within the view
+    textView.setGravity(Gravity.CENTER);
+
+    // Set the layout parameters (width and height)
+    textView.setLayoutParams(
+        new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT));
+
+    // Set the text color using a resource
+    textView.setTextColor(getResources().getColor(R.color.text_green));
+
+    // Set the background color using a resource
+    textView.setBackgroundColor(getResources().getColor(R.color.white));
+
+    // Set the content view to display the TextView
+    setContentView(textView);
+  }
+}

example/android/javalib/3-linting/build.mill

@@ -0,0 +1,95 @@
+// == Linting with Basic Config
+
+// This Mill build configuration includes a linting step, which is essential for ensuring code
+// quality and adhering to best practices in Android development projects. Running the `androidLintRun` task
+// produces a detailed HTML report by default, identifying potential issues in the code, such as performance,
+// security, and usability warnings. This helps maintain the health and quality of the codebase.
+
+// In this example, we set a custom config to generate the report file in txt format and not HTML.
+
+//// SNIPPET:BUILD
+package build
+
+import mill._
+import mill.javalib.android.{AndroidSdkModule, AndroidLintModule}
+
+// Create and configure an Android SDK module to manage Android SDK paths and tools.
+object androidSdkModule0 extends AndroidSdkModule {
+  def buildToolsVersion = "35.0.0"
+  def bundleToolVersion = "1.17.2"
+}
+
+// Actual android application with linting config
+object app extends AndroidLintModule {
+  def androidSdkModule = mill.define.ModuleRef(androidSdkModule0)
+
+  // Set path to the custom `lint.xml` config file. It is usually at the root of the project
+  def androidLintConfigPath = Task { Some(PathRef(millSourcePath / "lint.xml")) }
+
+  // Set the linting report to be generated as a text file
+  def androidLintReportFmt = Task { "txt" }
+
+  // Set path to generated `.jar` files in this case (or `.class` files)
+  def classPath = Task.Source { androidJar() }
+
+  // Set path to the location of the project source codes
+  def sourcesPath = Task.Source { (millSourcePath / "src" / "main" / "java") }
+
+  // Specify additional flag options for Android Lint not defined in `AndroidLintModule`
+  def androidLintArgs: T[Seq[String]] = Task {
+    Seq(
+      "--classpath",
+      classPath().path.toString,
+      "--sources",
+      sourcesPath().path.toString
+    )
+  }
+
+}
+
+/** See Also: app/AndroidManifest.xml */
+
+// The `AndroidManifest.xml` file shown above is flawed with hardcoded string linting problem so it can be spoted by running the `androidLintRun` task.
+
+/** See Also: app/resources/values/colors.xml */
+/** See Also: app/resources/values/strings.xml */
+/** See Also: app/src/main/java/com/helloworld/app/MainActivity.java */
+/** See Also: app/lint.xml */
+
+// The `lint.xml` file shown above ignores the `MissingApplicationIcon` error in the code as
+// the project is for demostration. There are no icons for the demo project.
+
+////SNIPPET:END
+
+/** Usage
+
+> ./mill show app.androidLintRun  # Display full path to the linting report in text file
+".../out/app/androidLintRun.dest/report.txt"
+
+> cat out/app/androidLintRun.dest/report.txt # Display content of the linting report
+AndroidManifest.xml:3: Error: Avoid hardcoding the debug mode; leaving it out allows debug and release builds to automatically assign one [HardcodedDebugMode]
+
+> sed -i.bak 's/ android:debuggable="true"//g' app/AndroidManifest.xml # Fix the HardcodedDebugMode warning issue from `AndroidManifest.xml`
+
+> ./mill app.androidLintRun # Rerun it for new changes to reflect
+
+> cat out/app/androidLintRun.dest/report.txt # Check the content of report again
+No issues found.
+
+*/
+
+// == Linting with Custom Configurations
+
+// The commands below set the serverity level of `MissingApplicationIcon` to `warning` in the `lint.xml` file that was shown above
+// and run the `androidLintRun` task. Some output of the changes is shown below.
+
+/** Usage
+
+> sed -i.bak 's/severity="ignore"/severity="warning"/g' app/lint.xml # Set `MissingApplicationIcon` severity level to warning
+
+> ./mill app.androidLintRun # Rerun it for new changes to reflect
+
+> cat out/app/androidLintRun.dest/report.txt # Output the changes in the report
+AndroidManifest.xml:3: Warning: Should explicitly set android:icon, there is no default [MissingApplicationIcon]
+
+*/

scalalib/src/mill/javalib/android/AndroidAppModule.scala

@@ -339,4 +339,5 @@ trait AndroidAppModule extends JavaModule {
 
     PathRef(keystoreFile)
   }
+
 }

scalalib/src/mill/javalib/android/AndroidLintModule.scala

@@ -0,0 +1,78 @@
+package mill.javalib.android
+
+import mill._
+import mill.api.PathRef
+import mill.javalib.android.AndroidAppModule
+
+/**
+ * Android Lint Module for integrating the Android Lint tool in a Mill build.
+ *
+ * This module provides configuration options for executing Android Lint, including setting paths,
+ * specifying lint rules, managing reports, and more.
+ */
+@mill.api.experimental
+trait AndroidLintModule extends AndroidAppModule {
+
+  /**
+   * Specifies the file format of lint report. Available file formats are "html", "xml", "txt" and "sarif".
+   * Specifies additional arguments for the Android Lint tool.
+   * Allows for complete customization of the lint command.
+   */
+  def androidLintReportFmt: T[String] = Task { "html" }
+
+  /**
+   * Specifies the lint configuration XML file path. This allows setting custom lint rules or modifying existing ones.
+   */
+  def androidLintConfigPath: T[Option[PathRef]] = Task { None }
+
+  /**
+   * Specifies additional arguments for the Android Lint tool.
+   * Allows for complete customization of the lint command.
+   */
+  def androidLintArgs: T[Seq[String]] = Task { Seq.empty[String] }
+
+  /**
+   * Runs the Android Lint tool to generate a report on code quality issues.
+   *
+   * This method utilizes Android Lint, a tool provided by the Android SDK,
+   * to analyze the source code for potential bugs, performance issues, and
+   * best practices compliance. It generates a report in the specified format.
+   *
+   * The lint tool requires the Android SDK's command-line tools to be installed.
+   * The report is saved in the task's destination directory as "report.html".
+   *
+   * For more details on the Android Lint tool, refer to:
+   * [[https://developer.android.com/studio/write/lint]]
+   */
+  def androidLintRun: T[PathRef] = Task.Input {
+
+    val format = androidLintReportFmt()
+    val lintReport: os.Path = T.dest / s"report.$format"
+
+    // Map the report format to the corresponding lint command flag
+    val lintReportFlag = format match {
+      case "html" => "--html"
+      case "txt" => "--text"
+      case "xml" => "--xml"
+      case "sarif" => "--sarif"
+      case _ => throw new Exception(s"Unsupported report format: $format")
+    }
+
+    // Prepare the lint configuration argument if the config path is set
+    val configArg = androidLintConfigPath().map(config =>
+      Seq("--config", config.path.toString)
+    ).getOrElse(Seq.empty)
+
+    os.call(
+      Seq(
+        androidSdkModule().cmdlineToolsPath().path.toString + "/lint",
+        millSourcePath.toString,
+        lintReportFlag.toString,
+        lintReport.toString
+      ) ++ configArg ++ androidLintArgs()
+    )
+
+    PathRef(lintReport)
+  }
+
+}

scalalib/src/mill/javalib/android/AndroidSdkModule.scala

@@ -74,6 +74,14 @@ trait AndroidSdkModule extends Module {
     PathRef(sdkPath().path / "build-tools" / buildToolsVersion())
   }
 
+  /**
+   * Provides path to the Android cmdline tools for the selected version.
+   */
+  def cmdlineToolsPath: T[PathRef] = Task {
+    installAndroidSdkComponents()
+    PathRef(sdkPath().path / "cmdline-tools" / "latest" / "bin")
+  }
+
   /**
    * Provides path to D8 Dex compiler, used for converting Java bytecode into Dalvik bytecode.
    *