[PATCH v2 2/5] docs: sphinx-pre-install: check GNU Make version

[Chen Miao <chenmiao.ku@gmail.com>]

The kernel documentation build requires GNU Make 4.0 or newer, but the
Sphinx dependency checker only verifies that a make executable exists.
This lets incompatible make implementations pass the check and fail
later during the build.

Check the GNU Make version on all supported systems. Prefer a compatible
gmake command, which is how Homebrew provides GNU Make on macOS, and
fall back to make. Document the requirement and the macOS gmake
invocation.

Signed-off-by: Chen Miao <chenmiao.ku@gmail.com>
---
 Documentation/doc-guide/sphinx.rst |  4 ++-
 tools/docs/sphinx-pre-install      | 41 +++++++++++++++++++++++++++++-
 2 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/Documentation/doc-guide/sphinx.rst b/Documentation/doc-guide/sphinx.rst
index 1e105542a..4fb716e77 100644
--- a/Documentation/doc-guide/sphinx.rst
+++ b/Documentation/doc-guide/sphinx.rst
@@ -147,7 +147,9 @@ documentation. After installing MacTeX, restart the terminal or run
 ``eval "$(/usr/libexec/path_helper)"`` so its command-line tools are visible.
 The default virtualenv mode is recommended on macOS because PyYAML is
 installed from ``Documentation/sphinx/requirements.txt`` rather than from a
-Homebrew formula.
+Homebrew formula. The script also checks for GNU Make 4.0 or newer; when
+Homebrew provides it as ``gmake``, use ``gmake htmldocs`` instead of
+``make htmldocs``.
 
 Installing Sphinx Minimal Version
 ---------------------------------
diff --git a/tools/docs/sphinx-pre-install b/tools/docs/sphinx-pre-install
index 1b9d77ec3..54f36c3b8 100755
--- a/tools/docs/sphinx-pre-install
+++ b/tools/docs/sphinx-pre-install
@@ -40,6 +40,7 @@ from kdoc.python_version import PythonVersion
 
 RECOMMENDED_VERSION = PythonVersion("3.4.3").version
 MIN_PYTHON_VERSION = PythonVersion("3.7").version
+MIN_MAKE_VERSION = PythonVersion("4.0").version
 
 
 class DepManager:
@@ -308,6 +309,44 @@ class MissingCheckers(AncillaryMethods):
 
         return None
 
+    def get_make_version(self, cmd):
+        """Get the GNU Make version, or None if cmd is not GNU Make."""
+        if not cmd:
+            return None
+
+        try:
+            result = self.run(
+                [cmd, "--version"],
+                capture_output=True,
+                text=True,
+                check=True,
+            )
+        except (OSError, subprocess.CalledProcessError):
+            return None
+
+        match = re.search(
+            r"^GNU Make\s+([0-9]+(?:\.[0-9]+)*)", result.stdout, re.MULTILINE
+        )
+        if not match:
+            return None
+
+        return PythonVersion.parse_version(match.group(1))
+
+    def check_make(self):
+        """Check for GNU Make 4.0 or newer."""
+        candidates = (
+            os.environ.get("MAKE"),
+            self.which("gmake"),
+            self.which("make"),
+        )
+
+        for make in candidates:
+            version = self.get_make_version(make)
+            if version and version >= MIN_MAKE_VERSION:
+                return
+
+        self.deps.add_package("make", DepManager.SYSTEM_MANDATORY)
+
     def check_perl_module(self, prog, dtype):
         """
         Does perl have a dependency? Is it available?
@@ -1559,7 +1598,7 @@ class SphinxDependencyChecker(MissingCheckers):
         # Check for needed programs/tools
         self.check_perl_module("Pod::Usage", DepManager.SYSTEM_MANDATORY)
 
-        self.check_program("make", DepManager.SYSTEM_MANDATORY)
+        self.check_make()
         self.check_program("which", DepManager.SYSTEM_MANDATORY)
 
         self.check_program("dot", DepManager.SYSTEM_OPTIONAL)
-- 
2.50.1 (Apple Git-155)