Enhance GN string interpolation.

tools/gn/parser.cc

 // Copyright (c) 2013 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/parser.h"
 
 #include "base/logging.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/operators.h"
 #include "tools/gn/token.h"
@@ skipping 38 matching lines @@
     "\n"
     "      integer = [ \"-\" ] digit { digit } .\n"
     "\n"
     "  Leading zeros and negative zero are disallowed.\n"
     "\n"
     "String literals\n"
     "\n"
     "  A string literal represents a string value consisting of the quoted\n"
     "  characters with possible escape sequences and variable expansions.\n"
     "\n"
-    "      string    = `\"` { char | escape | expansion } `\"` .\n"
-    "      escape    = `\\` ( \"$\" | `\"` | char ) .\n"
-    "      expansion = \"$\" ( identifier | \"{\" identifier \"}\" ) .\n"
-    "      char      = /* any character except \"$\", `\"`, or newline */ .\n"
+    "      string           = `\"` { char | escape | expansion } `\"` .\n"
+    "      escape           = `\\` ( \"$\" | `\"` | char ) .\n"
+    "      BracketExpansion = \"{\" ( identifier | ArrayAccess | ScopeAccess "
+                              ") \"}\" .\n"
+    "      expansion        = \"$\" ( identifier | BracketExpansion ) .\n"
+    "      char             = /* any character except \"$\", `\"`, or newline "
+                             "*/ .\n"
     "\n"
     "  After a backslash, certain sequences represent special characters:\n"
     "\n"
     "          \\\"    U+0022    quotation mark\n"
     "          \\$    U+0024    dollar sign\n"
     "          \\\\    U+005C    backslash\n"
     "\n"
     "  All other backslashes represent themselves.\n"
     "\n"
     "Punctuation\n"
@@ skipping 12 matching lines @@
     "      File = StatementList .\n"
     "\n"
     "      Statement     = Assignment | Call | Condition .\n"
     "      Assignment    = identifier AssignOp Expr .\n"
     "      Call          = identifier \"(\" [ ExprList ] \")\" [ Block ] .\n"
     "      Condition     = \"if\" \"(\" Expr \")\" Block\n"
     "                      [ \"else\" ( Condition | Block ) ] .\n"
     "      Block         = \"{\" StatementList \"}\" .\n"
     "      StatementList = { Statement } .\n"
     "\n"
+    "      ArrayAccess = identifier \"[\" { identifier | integer } \"]\" .\n"
+    "      ScopeAccess = identifier \".\" identifier .\n"
     "      Expr        = UnaryExpr | Expr BinaryOp Expr .\n"
     "      UnaryExpr   = PrimaryExpr | UnaryOp UnaryExpr .\n"
     "      PrimaryExpr = identifier | integer | string | Call\n"
-    "                  | identifier \"[\" Expr \"]\"\n"
-    "                  | identifier \".\" identifier\n"
+    "                  | ArrayAccess | ScopeAccess\n"
     "                  | \"(\" Expr \")\"\n"
     "                  | \"[\" [ ExprList [ \",\" ] ] \"]\" .\n"
     "      ExprList    = Expr { \",\" Expr } .\n"
     "\n"
     "      AssignOp = \"=\" | \"+=\" | \"-=\" .\n"
     "      UnaryOp  = \"!\" .\n"
     "      BinaryOp = \"+\" | \"-\"                  // highest priority\n"
     "               | \"<\" | \"<=\" | \">\" | \">=\"\n"
     "               | \"==\" | \"!=\"\n"
     "               | \"&&\"\n"
@@ skipping 627 matching lines @@
         break;
       }
     }
 
     // Suffix comments were assigned in reverse, so if there were multiple on
     // the same node, they need to be reversed.
     if ((*i)->comments() && !(*i)->comments()->suffix().empty())
       const_cast<ParseNode*>(*i)->comments_mutable()->ReverseSuffix();
   }
 }