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 namespace {
  13
  14
  15 }  // namespace
  16
  17 const char kForEach[] = "foreach";
  18 const char kForEach_HelpShort[] =
  19     "foreach: Iterate over a list.";
  20 const char kForEach_Help[] =
  21     "foreach: Iterate over a list.\n"
  22     "\n"
  23     "  foreach(<loop_var>, <list>) {\n"
  24     "    <loop contents>\n"
  25     "  }\n"
  26     "\n"
  27     "  Executes the loop contents block over each item in the list,\n"
  28     "  assigning the loop_var to each item in sequence.\n"
  29     "\n"
  30     "  The block does not introduce a new scope, so that variable assignments\n"
  31     "  inside the loop will be visible once the loop terminates.\n"
  32     "\n"
  33     "  The loop variable will temporarily shadow any existing variables with\n"
  34     "  the same name for the duration of the loop. After the loop terminates\n"
  35     "  the loop variable will no longer be in scope, and the previous value\n"
  36     "  (if any) will be restored.\n"
  37     "\n"
  38     "Example\n"
  39     "\n"
  40     "  mylist = [ \"a\", \"b\", \"c\" ]\n"
  41     "  foreach(i, mylist) {\n"
  42     "    print(i)\n"
  43     "  }\n"
  44     "\n"
  45     "  Prints:\n"
  46     "  a\n"
  47     "  b\n"
  48     "  c\n";
  49 Value RunForEach(Scope* scope,
  50                  const FunctionCallNode* function,
  51                  const ListNode* args_list,
  52                  Err* err) {
  53   const std::vector<const ParseNode*>& args_vector = args_list->contents();
  54   if (args_vector.size() != 2) {
  55     *err = Err(function, "Wrong number of arguments to foreach().",
  56                "Expecting exactly two.");
  57     return Value();
  58   }
  59
  60   // Extract the loop variable.
  61   const IdentifierNode* identifier = args_vector[0]->AsIdentifier();
  62   if (!identifier) {
  63     *err = Err(args_vector[0], "Expected an identifier for the loop var.");
  64     return Value();
  65   }
  66   base::StringPiece loop_var(identifier->value().value());
  67
  68   // Extract the list, avoid a copy if it's an identifier (common case).
  69   Value value_storage_for_exec;  // Backing for list_value when we need to exec.
  70   const Value* list_value = NULL;
  71   const IdentifierNode* list_identifier = args_vector[1]->AsIdentifier();
  72   if (list_identifier) {
  73     list_value = scope->GetValue(list_identifier->value().value(), true);
  74     if (!list_value) {
  75       *err = Err(args_vector[1], "Undefined identifier.");
  76       return Value();
  77     }
  78   } else {
  79     // Not an identifier, evaluate the node to get the result.
  80     Scope list_exec_scope(scope);
  81     value_storage_for_exec = args_vector[1]->Execute(scope, err);
  82     if (err->has_error())
  83       return Value();
  84     list_value = &value_storage_for_exec;
  85   }
  86   if (!list_value->VerifyTypeIs(Value::LIST, err))
  87     return Value();
  88   const std::vector<Value>& list = list_value->list_value();
  89
  90   // Block to execute.
  91   const BlockNode* block = function->block();
  92   if (!block) {
  93     *err = Err(function, "Expected { after foreach.");
  94     return Value();
  95   }
  96
  97   // If the loop variable was previously defined in this scope, save it so we
  98   // can put it back after the loop is done.
  99   const Value* old_loop_value_ptr = scope->GetValue(loop_var);
 100   Value old_loop_value;
 101   if (old_loop_value_ptr)
 102     old_loop_value = *old_loop_value_ptr;
 103
 104   for (const auto& cur : list) {
 105     scope->SetValue(loop_var, cur, function);
 106     block->ExecuteBlockInScope(scope, err);
 107     if (err->has_error())
 108       return Value();
 109   }
 110
 111   // Put back loop var.
 112   if (old_loop_value_ptr) {
 113     // Put back old value. Use the copy we made, rather than use the pointer,
 114     // which will probably point to the new value now in the scope.
 115     scope->SetValue(loop_var, old_loop_value, old_loop_value.origin());
 116   } else {
 117     // Loop variable was undefined before loop, delete it.
 118     scope->RemoveIdentifier(loop_var);
 119   }
 120
 121   return Value();
 122 }
 123
 124 }  // namespace functions