Enable errorprone only by request.

The motivation is that errorprone produces different bytecode than javac
this confuses retrolambda's desugaring where it fails to correctly
desugar try-with-resources.

To enable errorprone one needs to run:

```
./gradlew :mylib:mytask withErrorProne
```

Author: vkryachko

README.md

@@ -63,6 +63,12 @@ Firebase Android libraries exercise all three types of tests recommended by the
 Depending on the requirements of the specific project, some or all of these
 tests may be used to support changes.
 
+> :warning: **Running tests with errorprone**
+>
+> To run with errorprone add `withErrorProne` to the command line, e.g.
+>
+> `./gradlew :<firebase-project>:check withErrorProne`.
+
 ### Unit Testing
 
 These are tests that run on your machine's local Java Virtual Machine (JVM). At

build.gradle

@@ -43,12 +43,11 @@ buildscript {
 }
 
 apply from: 'sdkProperties.gradle'
+apply from: "gradle/errorProne.gradle"
 
 ext {
     playServicesVersion = '16.0.1'
     supportAnnotationsVersion = '28.0.0'
-    errorproneVersion = '2.3.2'
-    errorproneJavacVersion = '9+181-r4173-1'
     googleTruthVersion = '0.45'
     robolectricVersion = '4.1'
 }
@@ -72,12 +71,7 @@ configure(subprojects) {
         jcenter()
         mavenLocal()
     }
-    apply plugin: 'net.ltgt.errorprone'
-    dependencies {
-        errorprone "com.google.errorprone:error_prone_core:$errorproneVersion"
-        errorproneJavac "com.google.errorprone:javac:$errorproneJavacVersion"
 
-    }
     apply plugin: 'com.github.sherter.google-java-format'
     googleJavaFormat {
         toolVersion = '1.7'
@@ -99,10 +93,6 @@ configure(subprojects) {
         exclude '**/package-info.java'
     }
 
-    tasks.withType(JavaCompile) {
-        options.errorprone.excludedPaths = '.*/build/generated/.*'
-    }
-
     apply plugin: "org.jlleitschuh.gradle.ktlint"
 }
 

gradle/errorProne.gradle

@@ -0,0 +1,35 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+def isErrorProneRequested = getGradle().getStartParameter().getTaskNames().contains("withErrorProne")
+
+def errorproneVersion = '2.3.2'
+def errorproneJavacVersion = '9+181-r4173-1'
+
+if (isErrorProneRequested) {
+    configure(subprojects) {
+        apply plugin: 'net.ltgt.errorprone'
+        dependencies {
+            errorprone "com.google.errorprone:error_prone_core:$errorproneVersion"
+            errorproneJavac "com.google.errorprone:javac:$errorproneJavacVersion"
+
+        }
+        tasks.withType(JavaCompile) {
+            options.errorprone.excludedPaths = '.*/build/generated/.*'
+        }
+    }
+}
+
+// marker task to enable errorprone diagnostics.
+task withErrorProne {}