Support @SuppressWarnings("all")

[tbroyer]

Immutables.org (similar to AutoValue) uses @SuppressWarnings("all") on the files they generate.

Their generated withers use reference equality as an optimization (returning this –the current immutable object– rather than a new immutable object that would be strictly identical): https://github.com/immutables/immutables/blob/d8075fc66be685696bb2ccba36085b2437e11545/value-processor/src/org/immutables/value/processor/Immutables.generator#L1391-L1400

This causes a lot of warnings during compilation (only for strings though):

warning: [StringEquality] String comparison using reference equality instead of value equality
    if (this.authorizationEndpoint == value) {
                                   ^
    (see http://errorprone.info/bugpattern/StringEquality)
  Did you mean 'if (Objects.equals(this.authorizationEndpoint, value)) {'?

because Error Prone doesn't recognize @SuppressWarnings("all").

(note: if you believe it's a really bad practice to suppress all warnings even in code generated by an annotation processor –i.e. code you don't control–, then I'll open an issue on Immutables.org so they emit @SuppressionWarnings("StringEquality") instead)

/cc @elucash

[tbroyer]

Workaround if you don't need "modify-by-copy" for your value types: disable it entirely.

// Disable modify-by-copy generation by Immutables.org
// to avoid StringEquality warnings from Error Prone
@Value.Style(
    defaults = @Value.Immutable(copy = false)
)
package com.example;

import org.immutables.value.Value;

Of course using the -Xep:StringEquality:OFF compiler argument would also work, but would then also ignore your own code.

Alternatively, maybe Error Prone could have an option to ignore warnings for code generated by annotation processors? (ignoring errors might not be a good idea)

---

BTW, apparently, at least Eclipse and IntelliJ IDEA support @SuppressWarnings("all").

[eaftan]

Sorry for the slow reply. We don't want to support @SuppressWarnings("all") because we want people to be precise in suppressing warnings, and to explain why it's safe to do so. For the code generator case, what if we turned off warnings for files with an @generated annotation? That would match what we do internally -- we don't show warnings on generated code, but we do issue errors.

[tbroyer]

👍
Works for me.

I wonder if that couldn't be triggered on any generated class (you have access to the information in the Filer right?) though, rather than relying on a @Generated annotation.

[cushon]

I'm finally getting around to implementing this. @tbroyer, any ideas on how to use the Filer to tell if the sources are generated? AFAICT javac doesn't really distinguish between file objects from generated and non-generated files.

I guess we could assume that -s is set to something reasonable and check if the file came from the source output folder...

[Stephan202]

If the code generator includes it in the produced source code, you could look for the javax.annotation.Generated annotation.

[cushon]

Yep, that's the same @Generated annotation eaftan and tbroyer mentioned above.

My plan is to add a flag that will suppress warnings in @generated code. Any fancier ways of recognizing annotation processor generated code would be in addition to recognizing @generated, not a replacement.

[elucash]

AFAIK, there are no standard ways to find out if specific file was generated by annotation processing API. Javac specific classes could possibly keep track of this, but then, processing rounds and different annotation processors come into play, and also annotation processing is not the only mean to generate code. Fancier ways to detect generated code could possibly cover only fraction of such cases and, in result, have low power-to-weight ratio. So, I think, relying on the presence @Generated annotation is reliable and sufficient enough.

[tbroyer]

@cushon I was initially thinking about intercepting calls to createSourceFile, or to getJavaFileForOutput of JavaFileManager (with JavaFileObject.Kind.SOURCE).

Looking at com.sun.tools.javac.processing.JavacFile though, I see there are getGeneratedSourceNames() and getGeneratedSourceFileObjects(), so if you have direct access to the JavacFiler between each processing round, you could probably know whether a class being compiled/processed is generated (either from the enclosing top-level class name, or the location of the file being compiled).

@elucash Not all generators include a @Generated annotation, if only because Android doesn't have it in its runtime so it has to be explicitly added as a dependency there. See google/auto#240, and I see Immutables.org does exactly that too: https://github.com/immutables/immutables/blob/d8075fc66be685696bb2ccba36085b2437e11545/value-processor/src/org/immutables/value/processor/Immutables.generator#L32-L34

[cushon]

@tbroyer thanks for the pointers. Getting the information out of the filer looks doable, but I think it ends up requiring hacky reflection. I'd prefer to avoid that.

I implemented the version that just checks for @Generated. Hopefully that gets us most of the way there. If there are a lot of generators that don't use the annotation or don't want to add a dependency on a third party copy of jsr250, we can always revisit this.

[tbroyer]

@cushon Thanks. Now eagerly awaiting the next error-prone release ;-)

[cushon]

The last release is only a week old, so it could be a few weeks before the next one. You could try it out with the snapshot releases, though: https://oss.sonatype.org/content/repositories/snapshots/com/google/errorprone/

[tbroyer]

Hmm, 2.0.5-SNAPSHOT doesn't work for me (and this is version 2.0.5-20150630.195032-3, which is what the Travis build deployed).

Repro-case:

1. clone https://github.com/ozwillo/ozwillo-kernel
2. git revert --no-commit aae39685c10b1a17579315e90cf444d2e94ae00f
3. edit build.gradle to use 2.0.5-SNAPSHOT:

repositories { maven { url 'https://oss.sonatype.org/content/repositories/snapshots/' } }
configurations.errorprone {
  resolutionStrategy.force 'com.google.errorprone:error_prone_core:2.0.5-SNAPSHOT'
}

Then run ./gradlew assemble:

:oasis-webapp:compileJava
…/oasis-webapp/build/generated/source/apt/main/oasis/usecases/ImmutableDeleteAppInstance.java:115: warning: [StringEquality] String comparison using reference equality instead of value equality
      if (this.instanceId == value) {
                          ^
    (see http://errorprone.info/bugpattern/StringEquality)
  Did you mean 'if (Objects.equals(this.instanceId, value)) {'?
error: warnings found and -Werror specified
…/oasis-webapp/build/generated/source/apt/main/oasis/usecases/ImmutableChangeOrganizationStatus.java:102: warning: [StringEquality] String comparison using reference equality instead of value equality
      if (this.requesterId == value) {
                           ^
    (see http://errorprone.info/bugpattern/StringEquality)
  Did you mean 'if (Objects.equals(this.requesterId, value)) {'?
…/oasis-webapp/build/generated/source/apt/main/oasis/usecases/ImmutableChangeAppInstanceStatus.java:341: warning: [StringEquality] String comparison using reference equality instead of value equality
      if (this.requesterId == value) {
                           ^
    (see http://errorprone.info/bugpattern/StringEquality)
  Did you mean 'if (Objects.equals(this.requesterId, value)) {'?
…/oasis-webapp/build/generated/source/apt/main/oasis/usecases/ImmutableChangeAppInstanceStatus.java:693: warning: [StringEquality] String comparison using reference equality instead of value equality
      if (this.instance_id == value) {
                           ^
    (see http://errorprone.info/bugpattern/StringEquality)
  Did you mean 'if (Objects.equals(this.instance_id, value)) {'?
1 error
4 warnings

[cushon]

I should have mentioned that it's behind a flag. Does passing -XepDisableWarningsInGeneratedCode work?

[tbroyer]

Indeed works much better ;-)
Thanks

[xenoterracide]

hmm... errorprone like this

    <errorprone.version>2.0.14</errorprone.version>
    <errorprone.plexuscompiler.version>2.8.1</errorprone.plexuscompiler.version>

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <compilerId>javac-with-errorprone</compilerId>
          <forceJavacCompilerUse>true</forceJavacCompilerUse>
          <showDeprecation>true</showDeprecation>
          <showWarnings>true</showWarnings>
          <compilerArgs>
            <arg>-Xep:MissingOverride:ERROR</arg>
            <arg>-XepDisableWarningsInGeneratedCode</arg>
          </compilerArgs>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>org.codehaus.plexus</groupId>
            <artifactId>plexus-compiler-javac-errorprone</artifactId>
            <version>${errorprone.plexuscompiler.version}</version>
          </dependency>
          <dependency>
            <groupId>com.google.errorprone</groupId>
            <artifactId>error_prone_core</artifactId>
            <version>${errorprone.version}</version>
          </dependency>
        </dependencies>
      </plugin>

getting this failure though on an immutables generated class.

[INFO] Compiling 13 source files to /pipeline/source/target/classes
/pipeline/source/target/generated-sources/annotations/com/xenoterracide/util/exception/TryPredicate.java:272: error: [MissingOverride] build implements method in Builder; expected @Override
    public TryPredicate<T> build() {
                           ^
    (see http://errorprone.info/bugpattern/MissingOverride)
  Did you mean '@Override public TryPredicate<T> build() {'?
1 error

I'd guess it's because it's an error and not a warning? I've set it to error because I want CI failures, but I also don't want it to fail on generated code.