tools/gn/function_foreach.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "tools/gn/err.h"
   6 #include "tools/gn/functions.h"
   7 #include "tools/gn/parse_tree.h"
   8 #include "tools/gn/scope.h"
   9
  10 namespace functions {
  11
  12 const char kForEach[] = "foreach";
  13 const char kForEach_HelpShort[] =
  14     "foreach: Iterate over a list.";
  15 const char kForEach_Help[] =
  16     "foreach: Iterate over a list.\n"
  17     "\n"
  18     "  foreach(<loop_var>, <list>) {\n"
  19     "    <loop contents>\n"
  20     "  }\n"
  21     "\n"
  22     "  Executes the loop contents block over each item in the list,\n"
  23     "  assigning the loop_var to each item in sequence.\n"
  24     "\n"
  25     "  The block does not introduce a new scope, so that variable assignments\n"
  26     "  inside the loop will be visible once the loop terminates.\n"
  27     "\n"
  28     "  The loop variable will temporarily shadow any existing variables with\n"
  29     "  the same name for the duration of the loop. After the loop terminates\n"
  30     "  the loop variable will no longer be in scope, and the previous value\n"
  31     "  (if any) will be restored.\n"
  32     "\n"
  33     "Example\n"
  34     "\n"
  35     "  mylist = [ \"a\", \"b\", \"c\" ]\n"
  36     "  foreach(i, mylist) {\n"
  37     "    print(i)\n"
  38     "  }\n"
  39     "\n"
  40     "  Prints:\n"
  41     "  a\n"
  42     "  b\n"
  43     "  c\n";
  44
  45 Value RunForEach(Scope* scope,
  46                  const FunctionCallNode* function,
  47                  const ListNode* args_list,
  48                  Err* err) {
  49   const std::vector<const ParseNode*>& args_vector = args_list->contents();
  50   if (args_vector.size() != 2) {
  51     *err = Err(function, "Wrong number of arguments to foreach().",
  52                "Expecting exactly two.");
  53     return Value();
  54   }
  55
  56   // Extract the loop variable.
  57   const IdentifierNode* identifier = args_vector[0]->AsIdentifier();
  58   if (!identifier) {
  59     *err = Err(args_vector[0], "Expected an identifier for the loop var.");
  60     return Value();
  61   }
  62   base::StringPiece loop_var(identifier->value().value());
  63
  64   // Extract the list, avoid a copy if it's an identifier (common case).
  65   Value value_storage_for_exec;  // Backing for list_value when we need to exec.
  66   const Value* list_value = nullptr;
  67   const IdentifierNode* list_identifier = args_vector[1]->AsIdentifier();
  68   if (list_identifier) {
  69     list_value = scope->GetValue(list_identifier->value().value(), true);
  70     if (!list_value) {
  71       *err = Err(args_vector[1], "Undefined identifier.");
  72       return Value();
  73     }
  74   } else {
  75     // Not an identifier, evaluate the node to get the result.
  76     Scope list_exec_scope(scope);
  77     value_storage_for_exec = args_vector[1]->Execute(scope, err);
  78     if (err->has_error())
  79       return Value();
  80     list_value = &value_storage_for_exec;
  81   }
  82   if (!list_value->VerifyTypeIs(Value::LIST, err))
  83     return Value();
  84   const std::vector<Value>& list = list_value->list_value();
  85
  86   // Block to execute.
  87   const BlockNode* block = function->block();
  88   if (!block) {
  89     *err = Err(function, "Expected { after foreach.");
  90     return Value();
  91   }
  92
  93   // If the loop variable was previously defined in this scope, save it so we
  94   // can put it back after the loop is done.
  95   const Value* old_loop_value_ptr = scope->GetValue(loop_var);
  96   Value old_loop_value;
  97   if (old_loop_value_ptr)
  98     old_loop_value = *old_loop_value_ptr;
  99
 100   for (const auto& cur : list) {
 101     scope->SetValue(loop_var, cur, function);
 102     block->Execute(scope, err);
 103     if (err->has_error())
 104       return Value();
 105   }
 106
 107   // Put back loop var.
 108   if (old_loop_value_ptr) {
 109     // Put back old value. Use the copy we made, rather than use the pointer,
 110     // which will probably point to the new value now in the scope.
 111     scope->SetValue(loop_var, old_loop_value, old_loop_value.origin());
 112   } else {
 113     // Loop variable was undefined before loop, delete it.
 114     scope->RemoveIdentifier(loop_var);
 115   }
 116
 117   return Value();
 118 }
 119
 120 }  // namespace functions