Add CodeGeneratorRequestWriter from Base; fix plugins to work with Gradle cache; fix ArtifactMetaPlugin working directory

[alexander-yevsyukov]

This is the receiving half of SpineEventEngine/base-libraries#938: CodeGeneratorRequestWriter is protoc-plugin tooling, not runtime API, so it moves from base into the tool-base module.

Changes

• Add CodeGeneratorRequestWriter under the new package io.spine.tools.code.proto (repackaged from io.spine.code.proto to avoid a split package across the spine-base and spine-tool-base artifacts, as discussed in the issue).
• Add CodeGeneratorRequestWriterSpec with a local constructRequest helper (in base the helper is shared with the parsing specs, which stay there).
• Fix code generation with the Gradle build cache enabled (see below).
• Make ArtifactMetaPlugin write its files under build/spine/artifact-meta instead of claiming the whole build/spine directory (see below).
• Bump version → 2.0.0-SNAPSHOT.400.

Gradle build cache fix

With org.gradle.caching=true, clean build failed in modules using the io.spine.generated-sources and io.spine.descriptor-set-file plugins (e.g., classic-codegen in this repository): compilation reported unresolved references because no generated code was present.

Root cause

The same pattern as SpineEventEngine/compiler#67. Both plugins do their work in doLast actions of the cacheable generateProto task without declaring the results as task outputs:

• GeneratedSourcePlugin copies the protoc output into $projectDir/generated/<sourceSet>/;
• DescriptorSetFilePlugin creates the desc.ref file next to the descriptor set file.

clean deletes generated/ and build/; the build cache then restores generateProto without executing it — only declared outputs are restored — so the copied sources and desc.ref are missing, and compilation fails. With the cache off, everything works only because the task always re-executes after clean.

Fix

• GeneratedSourcePlugin — declares $projectDir/generated/<sourceSet> as an output of generateProto, so the build cache stores and restores the copied code.
• DescriptorSetFilePlugin — declares desc.ref as an output (the .desc file itself is already a declared output of the Protobuf Gradle plugin).
• The generated source directories are now added to source sets via project.files(dir).builtBy(task). This fixes a latent gap exposed by the new test: in pure-Java projects compileJava did not depend on generateProto at all, because the plugin severs the dependency carried by the protoc output directories when replacing them with generated/.... In Spine repositories this was masked by the Kotlin compilation dependency arranged by setupKotlinCompile().

Testing

The new BuildCacheSpec runs build → clean → build via TestKit against a project applying both plugins, with a project-local build cache directory for hermeticity. The test project's clean deletes generated/ (mimicking the Spine convention), and a handwritten Java class refers to the generated code, so missing codegen fails the compilation.

• Cache on: asserts generateProto is FROM_CACHE, the generated code, desc.ref, and the descriptor set file are restored and re-packed into resources.
• Cache off: asserts the task re-executes normally after clean.

Verified both ways: with the output declarations temporarily removed, the cache-on test fails while the cache-off test passes; with the fix, both pass.

ArtifactMetaPlugin working directory

The plugin declared the whole build/spine directory as the output of its writeArtifactMeta task and as a main resources source directory. build/spine is the root working directory shared by all Spine plugins (see rootWorkingDir), where each plugin is expected to claim its own subdirectory. Claiming the root put the declared inputs of other Spine plugins' tasks — e.g., build/spine/compiler/{requests,settings} of launchSpineCompiler — inside the declared output tree of writeArtifactMeta. Gradle's missing-dependency validation then failed consumer builds:

Task ':base:launchSpineCompiler' uses this output of task ':base:writeArtifactMeta' without declaring an explicit or implicit dependency.

The actual files never intersected; only the declared trees overlapped.

The plugin now claims build/spine/artifact-meta. The metadata file keeps its path relative to the output directory, so the in-JAR resource path — META-INF/io.spine/<artifact-id>.meta, the contract of ArtifactMeta.loadFromResource — is unchanged, and the reading side needs no changes. A side benefit: working files of other plugins under build/spine can no longer be swept into packaged resources by processResources. Consumer repositories can drop mustRunAfter("writeArtifactMeta") workarounds once they depend on a tool-base version with this change.

Notes

• org.gradle.caching remains off in gradle.properties: this repository's own build applies the published protobuf-setup-plugins via the root buildscript classpath, which does not yet contain the fix. Re-enable once ToolBase.version in buildSrc points to a release with this change.
• In repositories where the Spine Compiler also writes into generated/<sourceSet> (e.g., validation), Gradle's overlapping-outputs detection makes it re-execute the affected tasks instead of restoring them — correct results, fewer cache hits. Separating output directories per producer is a follow-up beyond this PR.

https://claude.ai/code/session_01QkiJSc86Y7ocs1PeZMxJhX

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.45%. Comparing base (e50738d) to head (d7085b4).

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #181      +/-   ##
============================================
+ Coverage     90.40%   90.45%   +0.04%     
  Complexity      554      554              
============================================
  Files           122      122              
  Lines          2230     2241      +11     
  Branches        311      311              
============================================
+ Hits           2016     2027      +11     
  Misses           93       93              
  Partials        121      121              

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