add tools for generating shim headers

Closes https://github.com/dart-lang/sdk/pull/51612

GitOrigin-RevId: 7e71761d5f13e9dff8d60c0287cc12fda56f9642
Change-Id: I76400e00ead54d9fc3d0dae26c2468e8401f3de8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/286601
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

build/shim_headers.gni

@@ -0,0 +1,36 @@
+# Copyright 2016 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+template("shim_headers") {
+  action_name = "gen_${target_name}"
+  config_name = "${target_name}_config"
+  shim_headers_path = "${root_gen_dir}/shim_headers/${target_name}"
+  config(config_name) {
+    include_dirs = [ shim_headers_path ]
+  }
+  action(action_name) {
+    script = "//tools/generate_shim_headers.py"
+    args = [
+      "--generate",
+      "--headers-root",
+      rebase_path(invoker.root_path),
+      "--output-directory",
+      rebase_path(shim_headers_path),
+    ]
+    if (defined(invoker.prefix)) {
+      args += [
+        "--prefix",
+        invoker.prefix,
+      ]
+    }
+    args += invoker.headers
+    outputs = []
+    foreach(h, invoker.headers) {
+      outputs += [ shim_headers_path + "/" + rebase_path(invoker.root_path,"//") + "/" + h ]
+    }
+  }
+  group(target_name) {
+    deps = [ ":${action_name}" ]
+    all_dependent_configs = [ ":${config_name}" ]
+  }
+}

tools/generate_shim_headers.py

@@ -0,0 +1,111 @@
+#!/usr/bin/env python
+# Copyright 2012 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+Generates shim headers that mirror the directory structure of bundled headers,
+but just forward to the system ones.
+
+This allows seamless compilation against system headers with no changes
+to our source code.
+"""
+
+
+import optparse
+import os.path
+import sys
+
+
+SHIM_TEMPLATE = """
+#if defined(OFFICIAL_BUILD)
+#error shim headers must not be used in official builds!
+#endif
+"""
+
+
+def GeneratorMain(argv):
+  parser = optparse.OptionParser()
+  parser.add_option('--headers-root', action='append')
+  parser.add_option('--define', action='append')
+  parser.add_option('--output-directory')
+  parser.add_option('--prefix', default='')
+  parser.add_option('--use-include-next', action='store_true')
+  parser.add_option('--outputs', action='store_true')
+  parser.add_option('--generate', action='store_true')
+
+  options, args = parser.parse_args(argv)
+
+  if not options.headers_root:
+    parser.error('Missing --headers-root parameter.')
+  if not options.output_directory:
+    parser.error('Missing --output-directory parameter.')
+  if not args:
+    parser.error('Missing arguments - header file names.')
+
+  source_tree_root = os.path.abspath(
+    os.path.join(os.path.dirname(__file__), '..'))
+
+  for root in options.headers_root:
+    target_directory = os.path.join(
+      options.output_directory,
+      os.path.relpath(root, source_tree_root))
+    if options.generate and not os.path.exists(target_directory):
+      os.makedirs(target_directory)
+
+    for header_spec in args:
+      if ';' in header_spec:
+        (header_filename,
+         include_before,
+         include_after) = header_spec.split(';', 2)
+      else:
+        header_filename = header_spec
+        include_before = ''
+        include_after = ''
+      if options.outputs:
+        yield os.path.join(target_directory, header_filename)
+      if options.generate:
+        header_path = os.path.join(target_directory, header_filename)
+        header_dir = os.path.dirname(header_path)
+        if not os.path.exists(header_dir):
+          os.makedirs(header_dir)
+        with open(header_path, 'w') as f:
+          f.write(SHIM_TEMPLATE)
+
+          if options.define:
+            for define in options.define:
+              key, value = define.split('=', 1)
+              # This non-standard push_macro extension is supported
+              # by compilers we support (GCC, clang).
+              f.write('#pragma push_macro("%s")\n' % key)
+              f.write('#undef %s\n' % key)
+              f.write('#define %s %s\n' % (key, value))
+
+          if include_before:
+            for header in include_before.split(':'):
+              f.write('#include %s\n' % header)
+
+          include_target = options.prefix + header_filename
+          if options.use_include_next:
+            f.write('#include_next <%s>\n' % include_target)
+          else:
+            f.write('#include <%s>\n' % include_target)
+
+          if include_after:
+            for header in include_after.split(':'):
+              f.write('#include %s\n' % header)
+
+          if options.define:
+            for define in options.define:
+              key, value = define.split('=', 1)
+              # This non-standard pop_macro extension is supported
+              # by compilers we support (GCC, clang).
+              f.write('#pragma pop_macro("%s")\n' % key)
+
+
+def DoMain(argv):
+  return '\n'.join(GeneratorMain(argv))
+
+
+if __name__ == '__main__':
+  DoMain(sys.argv[1:])