rules: CC/auto: add "config_file" rule to generate a c/c++ header...

...starting from a template (aka configuration file), and using the
variables defined via a ["CC/auto", "config"] target.

For example, to use a CMake configuration file, the targets could be
defined as follows

	...
	, "foo-header-blueprint":
	  { "type": ["@", "rules", "CC/auto", "config_file"]
	  , "input": ["config.hpp.in"]
	  , "output": ["config.hpp"]
	  , "stage": ["foo"]
	  , "magic_string": ["cmakedefine"]
	  , "@only": ["true"]
	  }
	, "foo-header":
	  { "type": "configure"
	  , "target": "foo-header-blueprint"
	  , "config":
	    { "type": "let*"
	    , "bindings":
	      [ [ "defines"
	        , [ ["var", "\"string value\""]
	          , ["FOO_MAJOR_VERSION", "3"]
	          , ["use_this_feature", true]
	          ]
	        ]
	      ]
	    , "body": {"type": "env", "vars": ["defines"]}
	    }
	  }
	  ...

The file config.hpp.in may look as follows

	#ifndef config_cmake
	#define config_cmake

	#cmakedefine var
	#cmakedefine use_this_feature
	#cmakedefine01 use_this_feature
	#cmakedefine unused

	#define FOO_VERSION @FOO_MAJOR_VERSION@
	#define DONT_TOUCH_THIS ${FOO_MAJOR_VERSION}

	#endif

and the generated configuration file foo/config.hpp is

	#ifndef config_cmake
	#define config_cmake

	#define var "string value"
	#define use_this_feature
	#define use_this_feature 1
	/* #undef unused */

	#define FOO_VERSION 3
	#define DONT_TOUCH_THIS ${FOO_MAJOR_VERSION}

	#endif

1 files changed, 76 insertions, 0 deletions

diff --git a/CC/auto/config_runner.py b/CC/auto/config_runner.py
new file mode 100755
index 0000000..f938c27
--- /dev/null
+++ b/CC/auto/config_runner.py
@@ -0,0 +1,76 @@
+#!/usr/bin/python3
+
+# Copyright 2022 Huawei Cloud Computing Technology Co., Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import json
+import re
+from sys import argv
+from re import sub, match
+
+input_file = argv[1]
+param_file = argv[2]
+magic_string = argv[3]
+at_only = argv[4] == "true"
+
+
+with open(param_file) as f:
+    param = json.loads(f.read())
+
+# In many cases, CMake simply defines some variables (without any associated
+# value). We handle this situation by assigning to the boolean True the empty
+# string. Note that no False value should be found, because the right way to set
+# a variable to False in the TARGETS file is to *do not mention* that variable
+# at all.
+for k, v in param.items():
+    if isinstance(v, bool):
+        param[k] = ""
+
+with open(input_file) as i:
+    with open("out", "w") as o:
+        for line in i.readlines():
+            if x := re.search(
+                r"#(.*)(" + magic_string + r" )([ \t]*)([a-zA-Z0-9_]+)", line
+            ):
+                # get the VAR
+                key = x.groups()[-1]
+                if key in param:
+                    line = sub(
+                        f"{x.group()[1:]}",
+                        f"{x.groups()[0]}define {x.groups()[2]}{key} {param[key]}",
+                        line,
+                    )
+                else:
+                    line = f"/* #undef {x.groups()[-1]} */\n" 
+            if x := re.search(
+                r"#(.*)(" + magic_string + "01 )([ \t]*)([a-zA-Z0-9_]+)", line
+            ):
+                # get the VAR
+                key = x.groups()[-1]
+                line = sub(
+                    f"{x.group()[1:]}",
+                    f"{x.groups()[0]}define {x.groups()[2]}{key} "
+                    + str(1 if key in param else 0),
+                    line,
+                )
+            if match("#[ \t]*define", line):
+                if x := re.search(r"@([a-zA-Z0-9-_]+)@", line):
+                    key = x.groups()[0]
+                    line = sub(x.group(), param.get(key, ""), line)
+                if not at_only:
+                    if x := re.search(r"\${([a-zA-Z0-9-_]+)}", line):
+                        key = x.groups()[0]
+                        line = sub(r"\${" + key + r"}", param.get(key, ""), line)
+
+            print(line, end="", file=o)