Check absolute minumum CMake requirement (#6)

examples/minimal-program/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.18)
+cmake_minimum_required(VERSION 3.15)
 project(minimal-program-dev)
 
 # You can add development-specific options here, such as warnings, tests,

examples/minimal-program/pyproject.toml

@@ -32,6 +32,7 @@ directory = "src-python"
 include = ["CMakeLists.txt", "src/*"]
 
 [tool.py-build-cmake.cmake]
+minimum_version = "3.15"
 build_type = "RelWithDebInfo"
 source_path = "src"
 build_args = ["-j"]

examples/minimal-program/src/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.18)
+cmake_minimum_required(VERSION 3.15)
 project(minimal-program)
 
 # Add the executable to compile

examples/minimal/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.18)
+cmake_minimum_required(VERSION 3.17)
 project(minimal-dev)
 
 # You can add development-specific options here, such as warnings, tests,

examples/minimal/README.md

@@ -177,6 +177,7 @@ You can use the `exclude` option to exclude specific files.
 
 ```toml
 [tool.py-build-cmake.cmake]
+minimum_version = "3.17"
 build_type = "RelWithDebInfo"
 source_path = "src"
 build_args = ["-j"]
@@ -187,6 +188,10 @@ project. The most important option is the `source_path`, the folder containing
 your main CMakeLists.txt file. The `-j` flag enables parallel builds, and the 
 `install_components` option defines which CMake components to install. In this
 example, the `python_modules` component is defined in src/CMakeLists.txt.  
+The `minimum_version` option defines which version of CMake is required to build
+this project. If this version or newer is not found in the PATH, it is added as
+a build requirement and installed by the build frontend (e.g. pip) before 
+building.  
 There are many other options, see the py-build-cmake documentation for more 
 details.
 

examples/minimal/pyproject.toml

@@ -31,6 +31,7 @@ directory = "src-python"
 include = ["CMakeLists.txt", "src/*"]
 
 [tool.py-build-cmake.cmake]
+minimum_version = "3.17"
 build_type = "RelWithDebInfo"
 source_path = "src"
 build_args = ["-j"]

examples/minimal/src/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.18)
+cmake_minimum_required(VERSION 3.17)
 project(minimal)
 
 # Find the Python development files

examples/pybind11-project/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.18)
+cmake_minimum_required(VERSION 3.17)
 project(py-build-cmake VERSION 0.0.11)
 set(PY_VERSION_SUFFIX "a0")
 set(PY_FULL_VERSION ${PROJECT_VERSION}${PY_VERSION_SUFFIX})

examples/pybind11-project/pyproject.toml

@@ -36,7 +36,7 @@ include = ["CMakeLists.txt", "cmake/*.cmake", "src/*.cpp", "src/*.hpp"]
 exclude = []
 
 [tool.py-build-cmake.cmake]
-minimum_version = "3.18"
+minimum_version = "3.17"
 build_type = "Release"
 source_path = "." # Containing CMakeLists.txt
 options = { "WITH_PY_STUBS:BOOL" = "On" }

src/py_build_cmake/build.py

@@ -14,6 +14,10 @@
 
 from .config import Config
 
+from distlib.version import NormalizedVersion
+
+_CMAKE_MINIMUM_REQUIRED = NormalizedVersion('3.15')
+
 
 class _BuildBackend(object):
 
@@ -23,13 +27,12 @@ def __init__(self) -> None:
     def check_program_version(
         self,
         program: str,
-        minimum_version: Optional[str],
+        minimum_version: Optional[NormalizedVersion],
         name: Optional[str],
         check_version: bool = True,
     ):
         """Check if there's a new enough version of the given command available
         in PATH."""
-        from distlib.version import NormalizedVersion
         name = name or program
         try:
             # Try running the command
@@ -43,8 +46,8 @@ def check_program_version(
                 program_version = NormalizedVersion(m.group(0))
                 if self.verbose: print("Found", name, program_version)
                 # Check if the version is new enough
-                if minimum_version:
-                    if program_version < NormalizedVersion(minimum_version):
+                if minimum_version is not None:
+                    if program_version < minimum_version:
                         raise RuntimeError(f"{name} too old")
         except CalledProcessError as e:
             if self.verbose:
@@ -76,27 +79,33 @@ def get_requires_for_build_wheel(self, config_settings=None):
 
     def check_cmake_program(self, cfg: Config, deps: List[str]):
         assert cfg.cmake
-        min_cmake_ver = cfg.cmake[self.get_os_name()].get('minimum_version')
-        # If CMake in PATH doesn't work, add it as a build requirement
+        # Do we need to perform a native build?
+        native = not cfg.cross or self.needs_cross_native_build(cfg)
+        native_cfg = cfg.cmake[self.get_os_name()] if native else {}
+        # Do we need to perform a cross build?
+        cross = cfg.cross
+        cross_cfg = cfg.cmake.get('cross', {})
+        # Find the strictest version requirement
+        min_cmake_ver = max(
+            _CMAKE_MINIMUM_REQUIRED,
+            NormalizedVersion(native_cfg.get('minimum_version', '0.0')),
+            NormalizedVersion(cross_cfg.get('minimum_version', '0.0')),
+        )
+        # If CMake in PATH doesn't work or is too old, add it as a build
+        # requirement
         if not self.check_program_version('cmake', min_cmake_ver, "CMake"):
-            req = "cmake"
-            if min_cmake_ver: req += ">=" + min_cmake_ver
-            deps.append(req)
+            deps.append("cmake>=" + str(min_cmake_ver))
+
         # Check if we need Ninja
         cfgs = []
-        # Native build?
-        native = not cfg.cross
-        crossnative = self.needs_cross_native_build(cfg)
-        if native or crossnative:
-            cfgs.append(cfg.cmake[self.get_os_name()])
-        # Cross build?
-        cross = cfg.cross
-        if cross:
-            cfgs.append(cfg.cmake['cross'])
-        # Do any of the configs need Ninja as a generator?
+        if native: cfgs.append(native_cfg)
+        if cross: cfgs.append(cross_cfg)
+        # Do any of the configs require Ninja as a generator?
         needs_ninja = lambda c: 'ninja' in c.get('generator', '').lower()
         need_ninja = any(map(needs_ninja, cfgs))
         if need_ninja:
+            # If so, check if a working version exists in the PATH, otherwise,
+            # add it as a build requirement
             if not self.check_program_version('ninja', None, "Ninja"):
                 deps.append("ninja")