Add warning when Jetifier is enabled.

Fixes #82

doctor-plugin/src/main/java/com/osacky/doctor/DoctorExtension.kt

@@ -41,6 +41,11 @@ open class DoctorExtension(objects: ObjectFactory) {
      */
     val allowBuildingAllAndroidAppsSimultaneously = objects.property<Boolean>().convention(false)
 
+    /**
+     * Warn if using Android Jetifier
+     */
+    val warnWhenJetifierEnabled = objects.property<Boolean>().convention(true)
+
     /**
      * Configures `JAVA_HOME`-specific behavior.
      */

doctor-plugin/src/main/java/com/osacky/doctor/DoctorPlugin.kt

@@ -44,7 +44,8 @@ class DoctorPlugin : Plugin<Project> {
         val downloadSpeedMeasurer = DownloadSpeedMeasurer(buildOperations, extension, intervalMeasurer)
         val buildCacheConnectionMeasurer = BuildCacheConnectionMeasurer(buildOperations, extension, intervalMeasurer)
         val buildCacheKey = RemoteCacheEstimation((buildOperations as BuildOperations), target, clock)
-        val list = listOf(daemonChecker, javaHomeCheck, garbagePrinter, javaAnnotationTime, downloadSpeedMeasurer, buildCacheConnectionMeasurer, buildCacheKey)
+        val jetifierWarning = JetifierWarning(extension, target)
+        val list = listOf(daemonChecker, javaHomeCheck, garbagePrinter, javaAnnotationTime, downloadSpeedMeasurer, buildCacheConnectionMeasurer, buildCacheKey, jetifierWarning)
 
         garbagePrinter.onStart()
         javaAnnotationTime.onStart()

doctor-plugin/src/main/java/com/osacky/doctor/JetifierWarning.kt

@@ -0,0 +1,22 @@
+package com.osacky.doctor
+
+import org.gradle.api.Project
+
+class JetifierWarning(private val doctorExtension: DoctorExtension, private val project: Project) : BuildStartFinishListener {
+
+    override fun onStart() {
+    }
+
+    override fun onFinish(): List<String> {
+        val isJetifierEnabled = project.findProperty(jetifierFlag) as String?
+        if (doctorExtension.warnWhenJetifierEnabled.get() && isJetifierEnabled != null && isJetifierEnabled == "true") {
+            return listOf("Jetifier was enabled which means your builds are slower.")
+        } else {
+            return emptyList()
+        }
+    }
+
+    companion object {
+        const val jetifierFlag = "android.enableJetifier"
+    }
+}

doctor-plugin/src/test/java/com/osacky/doctor/JetifierWarningTest.kt

@@ -0,0 +1,71 @@
+package com.osacky.doctor
+
+import com.google.common.truth.Truth.assertThat
+import org.gradle.testkit.runner.GradleRunner
+import org.junit.Rule
+import org.junit.Test
+import org.junit.rules.TemporaryFolder
+
+class JetifierWarningTest {
+
+    @get:Rule
+    val testProjectRoot = TemporaryFolder()
+
+    val jetifierWarning = "Jetifier was enabled which means your builds are slower."
+
+    @Test
+    fun testJetifierEnabledShowsWarning() {
+        testProjectRoot.writeBuildGradle(
+            """
+                    |plugins {
+                    |  id "com.osacky.doctor"
+                    |}
+                    |doctor {
+                    |  disallowMultipleDaemons = false
+                    |  javaHome {
+                    |    ensureJavaHomeMatches = false
+                    |  }
+                    |}
+                """.trimMargin("|")
+        )
+
+        val result = GradleRunner.create()
+            .forwardOutput()
+            .withArguments("help", "-Pandroid.enableJetifier=true")
+            .withPluginClasspath()
+            .withProjectDir(testProjectRoot.root)
+            .build()
+
+        assertThat(result.output).contains("BUILD SUCCESSFUL")
+        assertThat(result.output).contains("Gradle Doctor Prescriptions")
+        assertThat(result.output).contains(jetifierWarning)
+    }
+
+    @Test
+    fun testJetifierDisabledShowNoWarning() {
+        testProjectRoot.writeBuildGradle(
+            """
+                    |plugins {
+                    |  id "com.osacky.doctor"
+                    |}
+                    |doctor {
+                    |  disallowMultipleDaemons = false
+                    |  javaHome {
+                    |    ensureJavaHomeMatches = false
+                    |  }
+                    |}
+                """.trimMargin("|")
+        )
+
+        val result = GradleRunner.create()
+            .forwardOutput()
+            .withArguments("help", "-Pandroid.enableJetifier=false")
+            .withPluginClasspath()
+            .withProjectDir(testProjectRoot.root)
+            .build()
+
+        assertThat(result.output).contains("BUILD SUCCESSFUL")
+        assertThat(result.output).doesNotContain(jetifierWarning)
+        assertThat(result.output).doesNotContain("Gradle Doctor Prescriptions")
+    }
+}