New tools.cmake.cmaketoolchain:enabled_blocks (#16563)

* CMakeToolchain block select

* better tests

conan/tools/cmake/toolchain/blocks.py

@@ -1326,6 +1326,15 @@ def __getitem__(self, name):
         return self._blocks[name]
 
     def process_blocks(self):
+        blocks = self._conanfile.conf.get("tools.cmake.cmaketoolchain:enabled_blocks",
+                                          check_type=list)
+        if blocks is not None:
+            try:
+                new_blocks = OrderedDict((b, self._blocks[b]) for b in blocks)
+            except KeyError as e:
+                raise ConanException(f"Block {e} defined in tools.cmake.cmaketoolchain"
+                                     f":enabled_blocks doesn't exist in {list(self._blocks.keys())}")
+            self._blocks = new_blocks
         result = []
         for b in self._blocks.values():
             content = b.get_rendered_content()

conans/model/conf.py

@@ -74,6 +74,7 @@
     "tools.cmake.cmaketoolchain:toolset_cuda": "(Experimental) Path to a CUDA toolset to use, or version if installed at the system level",
     "tools.cmake.cmaketoolchain:presets_environment": "String to define wether to add or not the environment section to the CMake presets. Empty by default, will generate the environment section in CMakePresets. Can take values: 'disabled'.",
     "tools.cmake.cmaketoolchain:extra_variables": "Dictionary with variables to be injected in CMakeToolchain (potential override of CMakeToolchain defined variables)",
+    "tools.cmake.cmaketoolchain:enabled_blocks": "Select the specific blocks to use in the conan_toolchain.cmake",
     "tools.cmake.cmake_layout:build_folder_vars": "Settings and Options that will produce a different build folder and different CMake presets names",
     "tools.cmake.cmake_layout:build_folder": "(Experimental) Allow configuring the base folder of the build for local builds",
     "tools.cmake.cmake_layout:test_folder": "(Experimental) Allow configuring the base folder of the build for test_package",

test/unittests/tools/cmake/test_cmaketoolchain.py

@@ -95,6 +95,34 @@ def test_select_blocks(conanfile):
     assert "########## 'preprocessor' block #############" not in content
 
 
+def test_enabled_blocks_conf(conanfile):
+    conanfile.conf.define("tools.cmake.cmaketoolchain:enabled_blocks", ["generic_system"])
+    toolchain = CMakeToolchain(conanfile)
+    content = toolchain.content
+    assert "########## 'generic_system' block #############" in content
+    assert "########## 'cmake_flags_init' block #############" not in content
+    assert "########## 'libcxx' block #############" not in content
+    assert "########## 'variables' block #############" not in content
+    assert "########## 'preprocessor' block #############" not in content
+
+    # remove multiple
+    conanfile.conf.define("tools.cmake.cmaketoolchain:enabled_blocks",
+                          ["generic_system", "cmake_flags_init"])
+    toolchain = CMakeToolchain(conanfile)
+    content = toolchain.content
+    assert "########## 'generic_system' block #############" in content
+    assert "########## 'cmake_flags_init' block #############" in content
+    assert "########## 'libcxx' block #############" not in content
+    assert "########## 'variables' block #############" not in content
+    assert "########## 'preprocessor' block #############" not in content
+
+    conanfile.conf.define("tools.cmake.cmaketoolchain:enabled_blocks", ["potato"])
+    toolchain = CMakeToolchain(conanfile)
+    with pytest.raises(ConanException) as e:
+        _ = toolchain.content
+    assert "Block 'potato' defined in tools.cmake.cmaketoolchain:enabled_blocks doesn't" in str(e)
+
+
 def test_dict_keys(conanfile):
     toolchain = CMakeToolchain(conanfile)
     assert "generic_system" in toolchain.blocks.keys()