ci: speed up environment setup and C++ builds

Author: SYMSCAE

.github/scripts/configure-matrix.py

@@ -1,11 +1,25 @@
 """Configure SCons and CxxTest for the CI matrix."""
 
+import json
 from pathlib import Path
 
-test_requirements = Path("requirements/tests.txt").read_text().splitlines()
+requirements = ["python"]
+for filename in ("build.txt", "conda.txt", "tests.txt"):
+    for line in (Path("requirements") / filename).read_text().splitlines():
+        spec = line.split("#", 1)[0].strip()
+        if spec and spec != "cxxtest":
+            requirements.append(spec)
+
 Path("build").mkdir(exist_ok=True)
-Path("build/matrix-tests.txt").write_text(
-    "\n".join(line for line in test_requirements if line.strip() != "cxxtest")
+Path("build/matrix-environment.yml").write_text(
+    json.dumps(
+        {
+            "name": "test",
+            "channels": ["conda-forge"],
+            "dependencies": requirements,
+        },
+        indent=2,
+    )
     + "\n"
 )
 
@@ -19,7 +33,16 @@
 env.Replace(CXXTEST=os.path.join(cxxtest, 'bin', 'cxxtestgen'),
             CXXTEST_INSTALL_DIR=cxxtest, CXXTEST_PYTHON=sys.executable)
 
-if env['PLATFORM'] != 'win32':
+if env['PLATFORM'] == 'win32':
+    from SCons.Platform.win32 import exec_spawn
+
+    # The outer CI shell already activates conda and SCons configures MSVC.
+    # /D stops each compiler/test-generator child from repeating cmd AutoRun.
+    def spawn_without_autorun(sh, escape, cmd, args, child_env):
+        return exec_spawn([sh, '/D', '/C', escape(' '.join(args))], child_env)
+
+    env['SPAWN'] = spawn_without_autorun
+else:
     env.Replace(CXX=os.environ.get('CXX', os.path.join(prefix, 'bin', 'c++')))
     env.Prepend(CCFLAGS=['-isystem' + os.path.join(prefix, 'include')])
     env.Append(LIBPATH=os.path.join(prefix, 'lib'))

.github/workflows/matrix-and-codecov.yml

@@ -10,6 +10,10 @@ on:
       - published
   workflow_dispatch:
 
+concurrency:
+  group: matrix-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name != 'release' }}
+
 jobs:
   matrix-coverage:
     name: C++ tests (${{ matrix.os }}, Python ${{ matrix.python-version }})
@@ -24,15 +28,19 @@ jobs:
           - os: ubuntu-latest
             shell: bash -l {0}
             build: coverage
+            jobs: 4
           - os: windows-latest
             shell: cmd /C CALL {0}
             build: fast
+            jobs: 4
           - os: macos-latest
             shell: bash -l {0}
             build: fast
+            jobs: 2
           - os: macos-15-intel
             shell: bash -l {0}
             build: fast
+            jobs: 4
     defaults:
       run:
         shell: ${{ matrix.shell }}
@@ -55,28 +63,26 @@ jobs:
           ref: 191adddb3876ab389c0c856e1c03874bf70f8ee4
           path: build/cxxtest
 
-      - name: Initialize miniconda
+      - name: Prepare C++ test configuration
+        shell: python {0}
+        run: |
+          import runpy
+          runpy.run_path('.github/scripts/configure-matrix.py')
+
+      - name: Create build environment
         uses: conda-incubator/setup-miniconda@v3
         with:
           activate-environment: test
           channels: conda-forge
           conda-remove-defaults: "true"
-          auto-update-conda: true
+          auto-update-conda: false
           auto-activate-base: false
           python-version: ${{ matrix.python-version }}
-
-      - name: Prepare C++ test configuration
-        run: python .github/scripts/configure-matrix.py
-
-      - name: Install requirements
-        run: >-
-          conda install --yes --override-channels -c conda-forge
-          --file requirements/build.txt
-          --file requirements/conda.txt
-          --file build/matrix-tests.txt
+          environment-file: build/matrix-environment.yml
+          channel-priority: strict
 
       - name: Build and run C++ tests
-        run: scons -j2 build=${{ matrix.build }} test
+        run: scons -j${{ matrix.jobs }} build=${{ matrix.build }} test
 
       - name: Generate coverage report
         if: runner.os == 'Linux' && matrix.python-version == '3.14'

.github/workflows/tests-on-pr.yml

@@ -4,6 +4,10 @@ on:
   pull_request:
   workflow_dispatch:
 
+concurrency:
+  group: tests-on-pr-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   tests-on-pr:
     runs-on: ubuntu-latest
@@ -23,7 +27,7 @@ jobs:
           activate-environment: test
           channels: conda-forge
           conda-remove-defaults: "true"
-          auto-update-conda: true
+          auto-update-conda: false
           auto-activate-base: false
 
       - name: Conda config
@@ -53,7 +57,7 @@ jobs:
       - name: Build and run C++ tests with coverage
         run: |
           "$CONDA_PREFIX/bin/c++" --version
-          scons build=coverage test
+          scons -j4 build=coverage test
 
       - name: Generate coverage report
         run: >-