fix(ci): read java_vendor before overwriting java_distribution - #4255

Why

In the matrix generator, per-row post-processing overwrote v.java_distribution with its string .value and only afterwards read .vendor from it:

v.java_distribution = v.java_distribution.value;   // now a string, e.g. ""oracle""
v.java_vendor = v.java_distribution.vendor;         // ""oracle"".vendor === undefined

So v.java_vendor was always undefined. It feeds jdkTestVendor=${{ matrix.java_vendor }} in main.yml, which sets the Gradle test toolchain vendor (JvmVendorSpec.matching(...) in build-logic/basics/src/main/kotlin/configureToolchain.kt). An empty value left the test JDK unconstrained by vendor.

What

Destructure value and vendor before the overwrite, so the read no longer depends on statement order:

const {value: javaDistribution, vendor: javaVendor} = v.java_distribution;
v.java_distribution = javaDistribution;
v.java_vendor = javaVendor;

The later v.java_distribution === ""oracle"" checks run after this block and rely on v.java_distribution already being the string value, which the fix preserves.

main.yml provisions the matching-vendor JDK via actions/setup-java with distribution: ${{ matrix.java_distribution }}, so pinning the vendor in the toolchain spec resolves against an already-installed JDK and does not need org.gradle.java.installations.auto-download.

The same bug and the same destructuring fix were applied in apache/jmeter""s .github/workflows/matrix.js.

How to verify

1. npm ci --prefix .github/workflows
2. MATRIX_JOBS=8 node .github/workflows/matrix.mjs
3. Every row now has a real java_vendor — one of amazon, bellsoft, microsoft, oracle, eclipse, azul — and none is undefined.

🤖 Generated with Claude Code