Recompile when dependencies change by wilx · Pull Request #1102 · apache/maven-compiler-plugin

wilx · 2026-07-31T21:46:21Z

Summary

persist the ordered class path and module path in the plugin-local dependencies.lst state file
collect persisted metadata and the current-build timestamp fallback in one cached scan per normalized dependency path, removing the previous duplicate traversal
record regular dependency files as size and modification time, and exploded dependency directories as a stable metadata fingerprint
trigger the existing changed dependency rebuild reason when dependencies are added, removed, reordered, relocated, or replaced at the same path
add unit coverage for the consolidated detector and integration coverage for dependency removal and same-path SNAPSHOT replacement

Why

The 3.x incremental check only considered dependency timestamps relative to the current Maven session. It could therefore miss a dependency removed between invocations or a JAR replaced at the same path before the next invocation, leaving stale application bytecode.

The persisted comparison and the existing session-relative fallback are now consolidated. A missing baseline still detects dependencies rebuilt during the current Maven invocation, while unchanged builds no longer walk exploded dependencies once for persisted state and again for the timestamp fallback.

Validation

JAVA_HOME=/opt/jdks/latest-8 /opt/maven/latest/bin/mvn clean verify — 36 tests passed
JAVA_HOME=/opt/jdks/latest-21 /opt/maven/latest/bin/mvn clean verify — 36 tests passed
focused MCOMPILER-349, MCOMPILER-474, dependency-removal, and same-path-replacement integration tests passed
JAVA_HOME=/opt/jdks/latest-21 /opt/maven/latest/bin/mvn -Prun-its clean verify — 78 builds passed, 5 environment-specific skips

Fixes #1087

Following this checklist to help us incorporate your
contribution quickly and easily:

An issue is filed for this change: No recompilation if the dependencies have changed #1087. This pull request addresses only that issue.
Each commit in the pull request has a meaningful subject line and body.
The pull request title describes the issue. The template's [MCOMPILER-XXX] convention is not applicable because this is tracked as GitHub issue No recompilation if the dependencies have changed #1087.
The pull request description explains what the pull request does, how, and why.
Ran mvn clean verify.
Ran the integration tests successfully with mvn -Prun-its clean verify.

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elharo · 2026-08-07T11:13:18Z

+        }
+        if (changedDependency != null) {
+            if (configuration.log.isDebugEnabled() || configuration.showChanges) {
+                configuration.log.info("\tNew dependency detected: " + changedDependency.toAbsolutePath());


I wouldn't log this above debug level

The log.info is there because it is possible to get the line printed with user supplied maven.compiler.showCompilationChanges property. If it were log.debug it would not print if the user asked via the property. I can change it to debug for configuration.log.isDebugEnabled() and keep the info for configuration.showChanges. But that seems unnecessarily nuanced.

I only see one call of this method?

I agree here with @wilx not needed to do more complicated

elharo · 2026-08-07T11:14:18Z

+            }
+        }
+
+        List<Path> files;


This belongs inside the try, as does all the code that depends on it. Don't split variable declaration and initialization

elharo · 2026-08-07T11:15:38Z

+                    changedDependency = file;
+                }
+            } catch (IOException e) {
+                if (!unreadable) {


should you just break out of the loop in this case?

Fixed by merging the two try/catch regions.

elharo · 2026-08-07T11:20:47Z

+
+        if (hasPreviousState && !oldState.equals(newState)) {
+            if (configuration.log.isDebugEnabled() || configuration.showChanges) {
+                logChanges(oldState, newState, configuration.log);


checking debug here is good, but it's info level in the logChanges method. logChanges should log at debug level

It is already gated by maven.compiler.showCompilationChanges property.

elharo · 2026-08-07T15:32:39Z

+        }
+        if (changedDependency != null) {
+            if (configuration.log.isDebugEnabled() || configuration.showChanges) {
+                configuration.log.info("\tNew dependency detected: " + changedDependency.toAbsolutePath());


I only see one call of this method?

elharo · 2026-08-22T11:00:24Z

-     *
-     * @return {@code true} if at least one single dependency has changed.
-     */
-    protected boolean isDependencyChanged() {


This method should be retained with protected access, even if it's implementation changes

I'm not sure if we need to preserve all plugin internal methods.
Maven plugin is not library so should be not used as standard dependencies.

Even more we only recommended use as plugin not dependencies
https://maven.apache.org/plugins/maven-compiler-plugin/dependency-info.html

slawekjaranowski · 2026-08-26T09:23:52Z

@wilx please rebase

Persist ordered classpath and module-path dependency state between plugin invocations. Compare file metadata and stable directory fingerprints while preserving current-build timestamp detection in the same scan, so removed, reordered, relocated, and same-path replaced dependencies trigger recompilation without duplicate directory traversal. Fixes apache#1087

…gle try/catch.

wilx · 2026-08-26T16:53:03Z

@wilx please rebase

Done.

slawekjaranowski · 2026-08-26T17:48:13Z

@elharo does your comments resolved?

elharo

some of my original comments are answered, a couple are not

elharo · 2026-08-26T19:12:28Z

-     *
-     * @return {@code true} if at least one single dependency has changed.
-     */
-    protected boolean isDependencyChanged() {


elharo · 2026-08-26T19:14:31Z

+        StringBuilder buffer = new StringBuilder(bytes.length * 2);
+        for (byte value : bytes) {
+            int unsigned = value & 0xFF;
+            buffer.append(Character.forDigit(unsigned >>> 4, 16));


I'd just use Integer.toHexString here

Preserve the fixed two-character representation by prepending a zero when the converted byte has only one hexadecimal digit.

wilx marked this pull request as ready for review July 31, 2026 21:48

wilx marked this pull request as draft July 31, 2026 22:19

wilx force-pushed the issue-1087-dependency-state branch from 3d01630 to 665f6cf Compare July 31, 2026 22:42

wilx marked this pull request as ready for review July 31, 2026 22:43

wilx force-pushed the issue-1087-dependency-state branch from 665f6cf to 096cfb4 Compare July 31, 2026 23:25

elharo requested changes Aug 7, 2026

View reviewed changes

elharo requested a review from gnodet August 7, 2026 11:21

elharo reviewed Aug 22, 2026

View reviewed changes

desruisseaux added enhancement New feature or request 3.x labels Aug 24, 2026

wilx added 3 commits August 26, 2026 18:48

DependencyState: Merge directory walk and digest computation into sin…

502158a

…gle try/catch.

Use if for dependency change detection

12013c6

wilx force-pushed the issue-1087-dependency-state branch from e237a3a to 12013c6 Compare August 26, 2026 16:52

slawekjaranowski linked an issue Aug 26, 2026 that may be closed by this pull request

No recompilation if the dependencies have changed #1087

Open

slawekjaranowski approved these changes Aug 26, 2026

View reviewed changes

elharo requested changes Aug 26, 2026

View reviewed changes

Use Integer.toHexString for dependency state digest

920838b

Preserve the fixed two-character representation by prepending a zero when the converted byte has only one hexadecimal digit.

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slawekjaranowski commented Aug 26, 2026

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wilx commented Jul 31, 2026 •

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wilx Aug 7, 2026 •

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