Affects Version/s: 3.1
Fix Version/s: None
The compiler plugin has the useIncrementalCompilation flag. However, when this flag is set to true and using the javac compiler, the compilation is not very incremental; the compiler always at least claims it is rebuilding all source files (and compile times are consistent with this being what it is actually doing, though it is hard to tell). If I set useIncrementalCompilation to false, then it actually does report that some modules are up-to-date, and some only need a subset of their files compiled.
It seems that one or more of the following is happening:
- useIncrementalCompilation has some meaning that is very different from what a user would expect, actually controlling whether the compiler plugin uses some internal incremental compilation mechanism vs. incremental compilation support built-in to the particular compiler backend. One would expect this flag to turn on incremental compilation vs. build-everything.
- The log messages do not reflect what it is actually doing; that is, it seems possible that it's saying "Compiling 164 source files" when it's really handing 164 source files off to the compiler for potential compilation. If this is the case, it is very confusing and misleading.
- The logic of useIncrementalCompilation is just inverted. Looking at the source code for the abstract compiler MOJO, it doesn't look like it's quite this simple, but I also don't know what all the various components at work are doing.
- There is a bug in the implementation of useIncrementalCompilation.
The result of all this is incremental compilation with Maven is very confusing and difficult to understand.