ENH: Added -j auto for build cmd

spin/cmds/meson.py

@@ -252,8 +252,7 @@ def _check_coverage_tool_installation(coverage_type: GcovReportFormat, build_dir
     "-j",
     "--jobs",
     metavar="N_JOBS",
-    help="Number of parallel tasks to launch",
-    type=int,
+    help="Number of parallel tasks to launch. Can be set to `auto` to use all cores.",
 )
 @click.option("--clean", is_flag=True, help="Clean build directory before build")
 @click.option(
@@ -364,9 +363,24 @@ def build(
 
         # Any other conditions that warrant a reconfigure?
 
+    if jobs is not None:
+        if jobs == "auto":
+            jobs = str(os.cpu_count() or 1)
+        else:
+            try:
+                jobs = str(int(jobs))
+            except ValueError as err:
+                raise click.BadParameter(
+                    f"Expected an integer or 'auto', got '{jobs}'", param_hint="'-j'"
+                ) from err
+
     compile_flags = ["-v"] if verbose else []
     if jobs:
-        compile_flags += ["-j", str(jobs)]
+        if not quiet:
+            click.secho(
+                f"Building with {jobs} parallel jobs", bold=True, fg="bright_blue"
+            )
+        compile_flags += ["-j", jobs]
 
     p = _run(
         _meson_cli()

spin/tests/test_build_cmds.py

@@ -36,6 +36,20 @@ def test_debug_builds(example_pkg):
     assert len(list(debug_files)) != 0, "debug files not generated for gcov build"
 
 
+def test_build_jobs_auto(example_pkg):
+    """Does `spin build -j auto` work?"""
+    p = spin("build", "-j", "auto")
+    assert b"Building with" in p.stdout
+    assert b"parallel jobs" in p.stdout
+
+
+def test_build_jobs_invalid(example_pkg):
+    """Does `spin build -j nan` fail with a clear error?"""
+    p = spin("build", "-j", "nan", sys_exit=False)
+    assert p.returncode != 0
+    assert b"Expected an integer or 'auto'" in p.stderr
+
+
 def test_prefix_builds(example_pkg):
     """does spin build --prefix create a build-install directory with the correct structure?"""
     spin("build", "--prefix=/foobar/")