Instrumented every build configuration and merged their coverage (#665)

Only default_build_coverage carried -fprofile-arcs, because the gate was the
build type and it is the only one of five whose name ends in _coverage. The
other four build and run all their tests and their coverage was discarded. That
is not redundancy thrown away: each configuration selects a different set of TX_
feature macros, so the code the other four compile is absent from the
denominator rather than uncovered in it.

TX_COVERAGE instruments a build regardless of its name, defaulting to OFF so a
single configuration built by hand behaves as before. coverage.sh gains a
--merge mode that unions the per-configuration JSON tracefiles, and
cmake_bootstrap.sh runs it after the test loop so a local run produces the same
merged report CI reads. The template sets TX_COVERAGE for build and test, and
coverage_name moves to the merged report.

Measured on the ThreadX suite, all 480 tests passing:

  default_build_coverage           3827 valid   3827 covered
  disable_notify_callbacks_build   3767         3766
  stack_checking_build             3857         3856
  stack_checking_rand_fill_build   3862         3861
  trace_build                      4123         4108
  merged                           4503         4487

The denominator grows by 676 lines, 17.7%, and the figure moves from 99.97% to
99.64%. The second one is honest, and the drop is the point rather than a
regression: the denominator now includes code the old report never counted. The
union also contains a file the old report did not contain at all --
tx_thread_stack_error_handler.c compiles only under TX_ENABLE_STACK_CHECKING, so
it was not listed at 0%, it was simply absent. 177 files becomes 178.

Coverage collection moved out of test() and now runs after the test loop, one
configuration at a time. gcov writes its intermediate gcov files into the
directory gcovr is rooted at, and coverage.sh roots every configuration at the
repository root so filenames come out repo-relative. Five concurrent gcovr
processes therefore share one scratch directory and delete each other's output:
the first full run of this change passed all 480 tests and produced no report
for three of the five configurations. Measured both ways -- two gcovr rooted at
the repository root fail concurrently and succeed in sequence. CI would not
have caught it, because test_tx.sh sets CTEST_PARALLEL_LEVEL=1 and takes the
serial branch.

Per-configuration output moved under coverage_report/per_configuration/ and is
excluded from the Pages artifact. The deploy job merges the ThreadX and SMP
artifacts into one tree and every configuration directory has the same name in
both, so left at the top level one suite's would overwrite the other's on the
published site.

On the SMP suite, an earlier run of this change saw trace_build fail
threadx_smp_time_slice_test and then hang, which raised the question of whether
-fprofile-arcs perturbs a timing-sensitive test. It does not. Sixteen runs
settle it, and the decisive one is that threadx_smp_time_slice_test failed
ERROR #31 -- twice in a row under --repeat until-pass:2 -- on an uninstrumented
build, in the exact shape CI runs, while three instrumented runs of that shape
passed 5 of 5. In the CI shape, CTEST_PARALLEL_LEVEL=1 run.sh test all:

  TX_COVERAGE=OFF   3 runs   2 green, one ERROR #31        310 s
  TX_COVERAGE=ON    3 runs   3 green, 5/5 each             325-329 s

So the test is a pre-existing flake on dev and instrumenting all five costs
about 5% of the suite's wall clock. Separately, and also in both instrumented
and uninstrumented builds, run.sh's parallel branch -- what a developer gets
typing run.sh test all with no CTEST_PARALLEL_LEVEL -- hangs under its own load,
four times in twelve runs. Several SMP tests create 1024 ThreadX threads by
construction and the Linux port backs each with a pthread, so five
configurations at once put on the order of 5000 threads on the machine. CI sets
CTEST_PARALLEL_LEVEL=1 and does not take that branch.

Assisted-by: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/regression_template.yml

@@ -29,8 +29,13 @@ on:
         default: false
         required: false
         type: boolean
+      # The merged report, not one configuration's. Every configuration is
+      # instrumented now (TX_COVERAGE below) and coverage.sh --merge unions
+      # them; default_build_coverage was one build of five, and the code the
+      # other four select was absent from its denominator rather than uncovered
+      # in it.
       coverage_name:
-        default: 'default_build_coverage'
+        default: 'merged'
         required: false
         type: string
       skip_deploy:
@@ -79,12 +84,20 @@ jobs:
       timeout-minutes: 10
       run: ${{ inputs.install_script }}
 
+    # TX_COVERAGE instruments every build configuration rather than only the one
+    # whose name ends in _coverage. It has to be set for the build as well as the
+    # test: the build is where -fprofile-arcs is decided, and the test run is
+    # where the reports are collected and merged.
     - name: Build
       timeout-minutes: 15
+      env:
+        TX_COVERAGE: ${{ inputs.skip_coverage && 'OFF' || 'ON' }}
       run: ${{ inputs.build_script }}
 
     - name: Test
       timeout-minutes: 60
+      env:
+        TX_COVERAGE: ${{ inputs.skip_coverage && 'OFF' || 'ON' }}
       run: ${{ inputs.test_script }}
 
     - name: Publish Test Results
@@ -163,12 +176,32 @@ jobs:
       if: ${{ !cancelled() && (!inputs.skip_coverage) }}
       run: echo "coverage_report=coverage_report-$(date +%s)" >> $GITHUB_OUTPUT
 
+    # per_configuration is excluded deliberately. deploy_code_coverage downloads
+    # every coverage_report-* artifact with merge-multiple, so whatever is in
+    # here lands on the published site -- and each suite's per-configuration
+    # directories carry the same names, so ThreadX's would overwrite SMP's.
+    # The top level therefore holds only the suite directory and the merged XML,
+    # which is the shape the deploy already expects.
     - name: Upload Code Coverage Artifacts
       uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
       if: ${{ !cancelled() && (inputs.skip_deploy && !inputs.skip_coverage) }}
       with:
           name: ${{ steps.artifact.outputs.coverage_report }}
-          path: ${{ inputs.cmake_path }}/coverage_report
+          path: |
+            ${{ inputs.cmake_path }}/coverage_report
+            !${{ inputs.cmake_path }}/coverage_report/per_configuration/**
+          retention-days: 1
+
+    # The per-configuration reports, kept separately so they are downloadable
+    # when the merged number moves and the question is which configuration moved
+    # it. The name deliberately does not match coverage_report-*, so the deploy
+    # job's pattern does not pick it up and it never reaches the published site.
+    - name: Upload Per-Configuration Coverage
+      uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+      if: ${{ !cancelled() && (!inputs.skip_coverage) }}
+      with:
+          name: coverage_detail ${{ inputs.result_affix }}
+          path: ${{ inputs.cmake_path }}/coverage_report/per_configuration
           retention-days: 1
 
     - name: Upload Code Coverage Pages