Optimize classpath pre-processing in java_stub_template.txt

[rsalvador]

The classpath pre-processing in this java_stub_template.txt loop:

bazel/src/main/java/com/google/devtools/build/lib/bazel/rules/java/java_stub_template.txt

Line 309 in fcfcb92

for path in ${CLASSPATH}; do

is slow for long classpaths. For example for classpaths with ~250,000 and ~700,000 entries the loop takes 28 and 50 seconds, respectively, on an intel MacBook. This change reduce the times to 1 second or less.

Fixes #19480

[fmeum]

@mai93 As the original author of d0ee889, would you be available to review this?

[sgowroji]

Hi @rsalvador, Could you please take a look at the failing checks?

[rsalvador]

Hi @sgowroji, seems to be an infra (No space left on device) error: https://buildkite.com/bazel/bazel-bazel-github-presubmit/builds/17414#018a8379-ac66-45cd-b1d3-5319ee26895b/663-3842

(11:23:45) ERROR: /Users/buildkite/builds/bk-imacpro-6/bazel/bazel-bazel-github-presubmit/src/test/shell/bazel/BUILD:655:8: Testing //src/test/shell/bazel:allowlist_test (shard 1 of 3) failed: I/O exception during sandboxed execution: /private/var/tmp/_bazel_buildkite/c960f1e32dbf1661ca10ecfcb6915aad/sandbox/darwin-sandbox/6590/execroot/_main/bazel-out (No space left on device)

I see other PRs that trigger a darwin build also failing with the same error.

[rsalvador]

Could this fix be available in the 6.4.0 release? Do I need to do anything for that?

[fmeum]

@bazel-io flag

[iancha1992]

@bazel-io fork 6.4.0