javac-diagnostics.md

Most Dagger errors are in the format:

src/main/java/dagger/playground/Playground.java:20: [Dagger/DuplicateBindings] dagger.playground.E is bound multiple times:
  A a();
    ^
      @Provides dagger.playground.E dagger.playground.Mod.first()
      @Provides dagger.playground.E dagger.playground.Mod.second()
  
      dagger.playground.E is injected at
          dagger.playground.D.<init>(e)
      dagger.playground.D is injected at
          dagger.playground.C.<init>(d)
      dagger.playground.C is injected at
          dagger.playground.B.<init>(c)
      dagger.playground.B is injected at
          dagger.playground.A.<init>(b)
      dagger.playground.A is provided at
          dagger.playground.Component.a()

package dagger.playground;

class A {
  @Inject A(B b) {}
}
class B {
  @Inject B(C c) {}
}
class C {
  @Inject C(D d) {}
}
class D {
  @Inject D(E e) {}
}

class E {}

@dagger.Module
interface Mod {
  @Provides
  static E first() {
    return new E();
  }
  
  @Provides
  static E second() {
    return new E();
  }
}

@dagger.Component(modules = Mod.class)
interface Component {
  A a();
}

The format is hard to read, for a few reasons:

• The file path, especially in larger projects, is quite long. It takes up a good chunk of the first line of the diagnostic. This is a general diagnostic problem not particular to Dagger
• Our errors are multiple lines, but weren't designed to match the behavior of javac's diagnostic formatting. This is probably because we do most of our unit testing with github.com/google-compile-testing, which returns the Diagnostic unformatted. Here's the openjdk revision that began splitting up diagnostics.