Support for excluding variable from forwarding via forward_variables_form.

tools/gn/function_forward_variables_from.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/scope.h"
 
 namespace functions {
 
 namespace {
 
 void ForwardAllValues(const FunctionCallNode* function,
                       Scope* source,
                       Scope* dest,
+                      const std::set<std::string>& exclusion_set,
                       Err* err) {
   Scope::MergeOptions options;
   // This function needs to clobber existing for it to be useful. It will be
   // called in a template to forward all values, but there will be some
   // default stuff like configs set up in both scopes, so it would always
   // fail if it didn't clobber.
   options.clobber_existing = true;
   options.skip_private_vars = true;
   options.mark_dest_used = false;
+  options.excluded_values = exclusion_set;
   source->NonRecursiveMergeTo(dest, options, function,
                               "source scope", err);
   source->MarkAllUsed();
 }
 
 void ForwardValuesFromList(Scope* source,
                            Scope* dest,
                            const std::vector<Value>& list,
+                           const std::set<std::string>& exclusion_set,
                            Err* err) {
   for (const Value& cur : list) {
     if (!cur.VerifyTypeIs(Value::STRING, err))
       return;
+    if (exclusion_set.find(cur.string_value()) != exclusion_set.end())
+      continue;
     const Value* value = source->GetValue(cur.string_value(), true);
     if (value) {
       // Use the storage key for the original value rather than the string in
       // "cur" because "cur" is a temporary that will be deleted, and Scopes
       // expect a persistent StringPiece (it won't copy). Not doing this will
       // lead the scope's key to point to invalid memory after this returns.
       base::StringPiece storage_key = source->GetStorageKey(cur.string_value());
       if (storage_key.empty()) {
         // Programmatic value, don't allow copying.
         *err = Err(cur, "This value can't be forwarded.",
@@ skipping 13 matching lines @@
 }  // namespace
 
 const char kForwardVariablesFrom[] = "forward_variables_from";
 const char kForwardVariablesFrom_HelpShort[] =
     "forward_variables_from: Copies variables from a different scope.";
 const char kForwardVariablesFrom_Help[] =
     "forward_variables_from: Copies variables from a different scope.\n"
     "\n"
     "  forward_variables_from(from_scope, variable_list_or_star)\n"
     "\n"
+    "  forward_variables_from(from_scope, variable_list_or_star,\n"

[brettw, 2016/01/25 20:44:41]

Check out the help for rebase_path, I used C++-style syntax for documenting the
default variables, and we should probably be consistent.

[sdefresne, 2016/01/26 11:59:44]

Done.

+    "                         variable_to_not_forward_list)\n"
+    "\n"
     "  Copies the given variables from the given scope to the local scope\n"
     "  if they exist. This is normally used in the context of templates to\n"
     "  use the values of variables defined in the template invocation to\n"
     "  a template-defined target.\n"
     "\n"
     "  The variables in the given variable_list will be copied if they exist\n"
     "  in the given scope or any enclosing scope. If they do not exist,\n"
     "  nothing will happen and they be left undefined in the current scope.\n"
     "\n"
     "  As a special case, if the variable_list is a string with the value of\n"
     "  \"*\", all variables from the given scope will be copied. \"*\" only\n"
     "  copies variables set directly on the from_scope, not enclosing ones.\n"
     "  Otherwise it would duplicate all global variables.\n"
     "\n"
     "  When an explicit list of variables is supplied, if the variable exists\n"
     "  in the current (destination) scope already, an error will be thrown.\n"
     "  If \"*\" is specified, variables in the current scope will be\n"
     "  clobbered (the latter is important because most targets have an\n"
     "  implicit configs list, which means it wouldn't work at all if it\n"
     "  didn't clobber).\n"
     "\n"
     "  The sources assignment filter (see \"gn help "
           "set_sources_assignment_filter\")\n"
     "  is never applied by this function. It's assumed than any desired\n"
     "  filtering was already done when sources was set on the from_scope.\n"
     "\n"
+    "  The second form of the function allows to give a list of variables not\n"
+    "  to forward. This is mostly useful when used in combination with \"*\".\n"
+    "\n"
     "Examples\n"
     "\n"
     "  # This is a common action template. It would invoke a script with\n"
     "  # some given parameters, and wants to use the various types of deps\n"
     "  # and the visibility from the invoker if it's defined. It also injects\n"
     "  # an additional dependency to all targets.\n"
     "  template(\"my_test\") {\n"
     "    action(target_name) {\n"
     "      forward_variables_from(invoker, [ \"data_deps\", \"deps\",\n"
     "                                        \"public_deps\", \"visibility\" "
                                                                          "])\n"
     "      # Add our test code to the dependencies.\n"
     "      # \"deps\" may or may not be defined at this point.\n"
     "      if (defined(deps)) {\n"
     "        deps += [ \"//tools/doom_melon\" ]\n"
     "      } else {\n"
     "        deps = [ \"//tools/doom_melon\" ]\n"
     "      }\n"
     "    }\n"
     "  }\n"
     "\n"
     "  # This is a template around either a target whose type depends on a\n"
     "  # global variable. It forwards all values from the invoker.\n"
     "  template(\"my_wrapper\") {\n"
     "    target(my_wrapper_target_type, target_name) {\n"
     "      forward_variables_from(invoker, \"*\")\n"
     "    }\n"
-    " }\n";
+    "  }\n"
+    "\n"
+    "  # This is a template around another template that uses a variable to\n"

[brettw, 2016/01/25 20:44:41]

How about "A template that wraps another. It adds behavior based on one
variable, and forwards all others to the nested target."

[sdefresne, 2016/01/26 11:59:44]

Done.

+    "  # initialize another variable and is only interested in that one.\n"
+    "  template(\"my_ios_test_app\") {\n"
+    "    ios_test_app(target_name) {\n"
+    "      forward_variables_from(invoker, \"*\", [\"test_bundle_name\"])\n"
+    "      if (!defined(extra_substitutions)) {\n"
+    "        extra_substitutions = []\n"
+    "      }\n"
+    "      extra_substitutions += [ \"BUNDLE_ID_TEST_NAME=$test_bundle_name\" "
+                                                                          "]\n"
+    "    }\n"
+    "  }\n";
 
 // This function takes a ListNode rather than a resolved vector of values
 // both avoid copying the potentially-large source scope, and so the variables
 // in the source scope can be marked as used.
 Value RunForwardVariablesFrom(Scope* scope,
                               const FunctionCallNode* function,
                               const ListNode* args_list,
                               Err* err) {
   const std::vector<const ParseNode*>& args_vector = args_list->contents();
-  if (args_vector.size() != 2) {
+  if (args_vector.size() != 2 && args_vector.size() != 3) {
     *err = Err(function, "Wrong number of arguments.",
-               "Expecting exactly two.");
+               "Expecting two or three arguments.");
     return Value();
   }
 
   // Extract the scope identifier. This assumes the first parameter is an
   // identifier. It is difficult to write code where this is not the case, and
   // this saves an expensive scope copy. If necessary, this could be expanded
   // to execute the ParseNode and get the value out if it's not an identifer.
   const IdentifierNode* identifier = args_vector[0]->AsIdentifier();
   if (!identifier) {
     *err = Err(args_vector[0], "Expected an identifier for the scope.");
     return Value();
   }
 
   // Extract the source scope.
   Value* value = scope->GetMutableValue(identifier->value().value(), true);
   if (!value) {
     *err = Err(identifier, "Undefined identifier.");
     return Value();
   }
   if (!value->VerifyTypeIs(Value::SCOPE, err))
     return Value();
   Scope* source = value->scope_value();
 
+  // Extract the exclusion list if defined.
+  std::set<std::string> exclusion_set;
+  if (args_vector.size() == 3) {
+    Value exclusion_value = args_vector[2]->Execute(scope, err);
+    if (err->has_error())
+      return Value();
+
+    if (exclusion_value.type() != Value::LIST) {
+      *err = Err(exclusion_value, "Not a valid list of variables to exclude.",
+                 "Expecting a list of strings.");
+      return Value();
+    }
+
+    for (const Value& cur : exclusion_value.list_value()) {
+      if (!cur.VerifyTypeIs(Value::STRING, err))
+        return Value();
+
+      exclusion_set.insert(exclusion_set.end(), cur.string_value());

[brettw, 2016/01/25 20:44:41]

I think you can just delete the first parameter.

[sdefresne, 2016/01/26 11:59:44]

Done.

+    }
+  }
+
   // Extract the list. If all_values is not set, the what_value will be a list.
   Value what_value = args_vector[1]->Execute(scope, err);
   if (err->has_error())
     return Value();
   if (what_value.type() == Value::STRING) {
     if (what_value.string_value() == "*") {
-      ForwardAllValues(function, source, scope, err);
+      ForwardAllValues(function, source, scope, exclusion_set, err);
       return Value();
     }
   } else {
     if (what_value.type() == Value::LIST) {
-      ForwardValuesFromList(source, scope, what_value.list_value(), err);
+      ForwardValuesFromList(source, scope, what_value.list_value(),
+                            exclusion_set, err);
       return Value();
     }
   }
 
   // Not the right type of argument.
   *err = Err(what_value, "Not a valid list of variables to copy.",
              "Expecting either the string \"*\" or a list of strings.");
   return Value();
 }
 
 }  // namespace functions