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
10namespace functions {
11
12namespace {
13
14
15}  // namespace
16
17const char kForEach[] = "foreach";
18const char kForEach_HelpShort[] =
19    "foreach: Iterate over a list.";
20const 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";
49Value 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());
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 (size_t i = 0; i < list.size(); i++) {
105    scope->SetValue(loop_var, list[i], 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
125