perf: skip reloadWorkspace() when compile tasks are all UP-TO-DATE

[wenytang-ms]

Problem

After every buildTargetCompile, the server unconditionally calls reloadWorkspace() to detect source root changes from code generation frameworks (e.g., Protocol Buffers). However, reloadWorkspace() is expensive — it does a full Gradle Tooling API model query (getGradleSourceSets()) which takes ~1-2s per call.

This is particularly wasteful during Eclipse auto-build cycles. After the initial compile, subsequent auto-builds produce all UP-TO-DATE tasks (no code changed), but reloadWorkspace() still runs every time:

auto-build → BuildServerBuilder.build()
  → BSP buildTargetCompile → all tasks UP-TO-DATE (~100ms)
  → reloadWorkspace() → full Tooling API round-trip (~1-2s) ← wasted!
  → model unchanged → no didChange
  → but auto-build may trigger again due to other resource changes
  → repeat 3-4 times before converging

This adds ~4-8s of unnecessary Gradle Tooling API overhead after each test run or debug launch.

Root Cause

BuildTargetService.compile() always schedules reloadWorkspace() after compilation, regardless of whether any work was actually done:

if (!Boolean.getBoolean("bsp.plugin.reloadworkspace.disabled")) {
    CompletableFuture.runAsync(this::reloadWorkspace);  // always runs
}

The information about whether tasks were UP-TO-DATE is already available in CompileProgressReporter.statusChanged() via TaskSuccessResult.isUpToDate() and TaskSkippedResult, but compile() doesn't use it.

Fix

• Add a hasExecutedWork flag to CompileProgressReporter that tracks whether any task performed actual work (not skipped, not UP-TO-DATE).
• In compile(), only call reloadWorkspace() when reporter.hasExecutedWork() is true.

When all tasks are UP-TO-DATE, no new files were produced, so the project model cannot have changed — reloadWorkspace() is safely skipped.

Risk Assessment

Risk	Level	Mitigation
Missing model changes after UP-TO-DATE compile	None	UP-TO-DATE means Gradle confirmed no outputs changed. Model is derived from Gradle project structure, not compile outputs.
Code generation (protobuf, annotation processors)	None	If codegen tasks produce new files, they won't be UP-TO-DATE — hasExecutedWork will be true and reload will happen normally.
External changes to build files	None	External changes cause tasks to not be UP-TO-DATE on next compile.

Performance Impact

For a workspace with 5 Gradle subprojects after running a test:

Metric	Before	After
Redundant reloadWorkspace() calls	3-4	0
Wasted Gradle Tooling API time	~4-8s	~0s

Related: microsoft/vscode-gradle#1794 (fixed the infinite rebuild loop; this PR reduces remaining convergence overhead)

[Copilot]

Pull request overview

Improves compile-time performance by avoiding expensive workspace model reloads after buildTargetCompile when Gradle reports that all relevant tasks were skipped or UP-TO-DATE.

Changes:

• Track whether any compile-related Gradle task performed real work via CompileProgressReporter.hasExecutedWork().
• Conditionally schedule reloadWorkspace() only when work was executed.
• Add informational logging around the reload decision.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
server/src/main/java/com/microsoft/java/bs/core/internal/services/BuildTargetService.java	Only schedules reloadWorkspace() after compile when tasks executed work; adds logging.
server/src/main/java/com/microsoft/java/bs/core/internal/reporter/CompileProgressReporter.java	Adds a flag to detect non-UP-TO-DATE/non-skipped task outcomes and exposes it to callers.

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