Michael Ekstrand created MCOMPILER-209:
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Summary: Incremental compilation doesn't work unless
useIncrementalCompilation is set to 'false'
Key: MCOMPILER-209
URL: https://jira.codehaus.org/browse/MCOMPILER-209
Project: Maven 2.x Compiler Plugin
Issue Type: Bug
Affects Versions: 3.1
Reporter: Michael Ekstrand
The compiler plugin has the
[useIncrementalCompilation|https://maven.apache.org/plugins/maven-compiler-plugin/compile-mojo.html#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.
The result of all this is incremental compilation with Maven is very confusing
and difficult to understand.
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