hunterpayne commented on PR #160:
URL:
https://github.com/apache/maven-compiler-plugin/pull/160#issuecomment-2070978534
I can tell you with 100% certainty that only tracking file timestamps won't
work and will be a bug farm. You must know which .class files are generated
from which .java files and in addition know which .class files depend upon
which other .class files. If this isn't possible, then it isn't possible to
implement this feature in a maintainable way. So either we need to track this
additional information, or relax the requirement to so, module level or package
level and track dependencies at that level. I am OK with either path but we
shouldn't go ahead with only tracking file timestamps and acting like that is a
working incremental build feature.
On Monday, April 22, 2024 at 02:17:06 PM PDT, Martin Desruisseaux
***@***.***> wrote:
While incremental builds is important, my reading of the source code
inherited from Maven 3 suggests that in its current state, incremental build
has bugs causing the opposite effect than what the plugin wanted to achieve. We
could try to fix the Maven 3 compiler plugin, but I do not know if it is worth
the effort given that the plugin is getting a significant rewrite for Maven 4.
The current useIncrementalCompilation parameter is a boolean flag which is
actually mixing at least two aspects: whether to check if a dependency changed,
and how to detect which source files changed. I suggest to deprecate that
parameter and replace it with a new incrementalCompilation parameter (same name
but without use prefix). The value of that parameter would be a comma-separated
list of the following:
- dependencies: check whether a dependency changed.
- sources: check whether a source file has been updated, or whether
source files were added or removed.
- classes: check whether a source file is more recent than its .class
file.
- modules (new): don't try to do incremental build in Maven, but delegate
that task to javac instead. This is possible only with modular projects. It
uses the --module compiler option, which is an alternative to enumerating all
source files on the command-line.
Equivalences with the current parameter:
- useIncrementalCompilation = true is equivalent to
incrementalCompilation = dependencies,sources (except maybe for the cases of
newly added source files).
- useIncrementalCompilation = false is equivalent to
incrementalCompilation = classes.
For an initial version of the Maven 4 compiler plugin, detection of changes
would be based only on file timestamps. This is the same strategy than the
current plugin. This approach would be unable to detect that a class needs to
be recompiled because it depends on another class which has been changed.
However, the current plugin cannot detect such cases neither, so we don't lost
anything. If we support that feature in the future, it would be one new value
in the above-cited list of comma-separated values.
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