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

2 files changed, 222 insertions, 0 deletions

diff --git a/rules/CC/auto/RULES b/rules/CC/auto/RULES
index 4f38504a..7d27ff62 100644
--- a/rules/CC/auto/RULES
+++ b/rules/CC/auto/RULES
@@ -952,4 +952,150 @@
       }
     }
   }
+, "config_file":
+  { "doc":
+    [ "Generate a C/C++ config header from a given template"
+    , ""
+    , "Generate a C/C++ configuration header using defines specified via the"
+    , "target configuration. In the usual case, a target using this rule is"
+    , "configured by depending on it from a target that uses the built-in"
+    , "\"configure\" rule."
+    ]
+  , "field_doc":
+    { "output":
+      [ "Name of the header file to generate (incl. file name ext). Components are joined with /."
+      ]
+    , "input": ["The input configuration file, used as template."]
+    , "magic_string":
+      [ "The magic string (e.g., \"cmakedefine\") which identifies in which line"
+      , "we have to \"#define\" or \"#undef\" variables according to what is"
+      , "defined in the config field \"defines\"."
+      ]
+    , "@only": ["If set, only replace @VAR@ and not ${VAR}"]
+    }
+  , "config_doc":
+    { "defines":
+      [ "Set a define to a specific value unless its value is \"null\". Must"
+      , "contain a list of pairs. The first element of each pair is the define"
+      , "name and the second argument is the value to set. Strings must be"
+      , "properly escaped. Defines generated from this field are added last,"
+      , "so that they can refer to defines from other \"defines*\" values."
+      ]
+    }
+  , "string_fields": ["magic_string", "@only", "output"]
+  , "target_fields": ["input"]
+  , "config_vars": ["defines"]
+  , "imports":
+    { "first": "first_list_entry"
+    , "last": "last_list_entry"
+    , "stage_singleton_field": ["", "stage_singleton_field"]
+    }
+  , "implicit": {"runner": ["config_runner.py"]}
+  , "expression":
+    { "type": "let*"
+    , "bindings":
+      [ [ "runner"
+        , { "type": "let*"
+          , "bindings": [["fieldname", "runner"], ["location", "runner"]]
+          , "body":
+            {"type": "CALL_EXPRESSION", "name": "stage_singleton_field"}
+          }
+        ]
+      , [ "dict-defines"
+        , { "type": "map_union"
+          , "$1":
+            { "type": "foreach"
+            , "range": {"type": "var", "name": "defines", "default": []}
+            , "var": "pair"
+            , "body":
+              { "type": "let*"
+              , "bindings":
+                [ ["list", {"type": "var", "name": "pair"}]
+                , ["key", {"type": "CALL_EXPRESSION", "name": "first"}]
+                , ["val", {"type": "CALL_EXPRESSION", "name": "last"}]
+                ]
+              , "body":
+                { "type": "singleton_map"
+                , "key": {"type": "var", "name": "key"}
+                , "value": {"type": "var", "name": "val"}
+                }
+              }
+            }
+          }
+        ]
+      , [ "magic_string"
+        , { "type": "assert_non_empty"
+          , "msg": "A non-empty string has to be provided for magic_string"
+          , "$1":
+            {"type": "join", "$1": {"type": "FIELD", "name": "magic_string"}}
+          }
+        ]
+      , [ "@only"
+        , { "type": "if"
+          , "cond": {"type": "FIELD", "name": "@only"}
+          , "then": "true"
+          , "else": "false"
+          }
+        ]
+      , [ "param-blob"
+        , { "type": "singleton_map"
+          , "key": "param-file"
+          , "value":
+            { "type": "BLOB"
+            , "data":
+              { "type": "json_encode"
+              , "$1": {"type": "var", "name": "dict-defines"}
+              }
+            }
+          }
+        ]
+      , [ "input-blob"
+        , { "type": "let*"
+          , "bindings": [["fieldname", "input"], ["location", "input-file"]]
+          , "body":
+            {"type": "CALL_EXPRESSION", "name": "stage_singleton_field"}
+          }
+        ]
+      , [ "outfile"
+        , { "type": "ACTION"
+          , "inputs":
+            { "type": "map_union"
+            , "$1":
+              [ {"type": "var", "name": "param-blob"}
+              , {"type": "var", "name": "input-blob"}
+              , {"type": "var", "name": "runner"}
+              ]
+            }
+          , "cmd":
+            [ "./runner"
+            , "input-file"
+            , "param-file"
+            , {"type": "var", "name": "magic_string"}
+            , {"type": "var", "name": "@only"}
+            ]
+          , "outs": ["out"]
+          }
+        ]
+      , [ "outfile"
+        , { "type": "singleton_map"
+          , "key":
+            { "type": "join"
+            , "separator": "/"
+            , "$1": {"type": "FIELD", "name": "output"}
+            }
+          , "value":
+            { "type": "lookup"
+            , "key": "out"
+            , "map": {"type": "var", "name": "outfile"}
+            }
+          }
+        ]
+      ]
+    , "body":
+      { "type": "RESULT"
+      , "artifacts": {"type": "var", "name": "outfile"}
+      , "runfiles": {"type": "var", "name": "outfile"}
+      }
+    }
+  }
 }
diff --git a/rules/CC/auto/config_runner.py b/rules/CC/auto/config_runner.py
new file mode 100755
index 00000000..f938c272
--- /dev/null
+++ b/rules/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)