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Unified Diff: tools/gn/parser.cc

Issue 1015063003: tools/gn: add "gn help grammar" with formal grammar (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Remove line requested by brettw Created 5 years, 9 months ago
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Index: tools/gn/parser.cc
diff --git a/tools/gn/parser.cc b/tools/gn/parser.cc
index 2a037fb24fa3a8275d3a05ae8327da902fbabe3c..1fa432e3a8061704d7cac1ea900948327140f582 100644
--- a/tools/gn/parser.cc
+++ b/tools/gn/parser.cc
@@ -9,14 +9,105 @@
#include "tools/gn/operators.h"
#include "tools/gn/token.h"
-// grammar:
-//
-// file := (statement)*
-// statement := block | if | assignment
-// block := '{' statement* '}'
-// if := 'if' '(' expr ')' statement [ else ]
-// else := 'else' (if | statement)*
-// assignment := ident {'=' | '+=' | '-='} expr
+const char kGrammar_Help[] =
+ "GN build language grammar\n"
+ "\n"
+ "Tokens\n"
+ "\n"
+ " GN build files are read as sequences of tokens. While splitting the\n"
+ " file into tokens, the next token is the longest sequence of characters\n"
+ " that form a valid token.\n"
+ "\n"
+ "White space and comments\n"
+ "\n"
+ " White space is comprised of spaces (U+0020), horizontal tabs (U+0009),\n"
+ " carriage returns (U+000D), and newlines (U+000A).\n"
+ "\n"
+ " Comments start at the character \"#\" and stop at the next newline.\n"
+ "\n"
+ " White space and comments are ignored except that they may separate\n"
+ " tokens that would otherwise combine into a single token.\n"
+ "\n"
+ "Identifiers\n"
+ "\n"
+ " Identifiers name variables and functions.\n"
+ "\n"
+ " identifier = letter { letter | digit } .\n"
+ " letter = \"A\" ... \"Z\" | \"a\" ... \"z\" | \"_\" .\n"
+ " digit = \"0\" ... \"9\" .\n"
+ "\n"
+ "Keywords\n"
+ "\n"
+ " The following keywords are reserved and may not be used as\n"
+ " identifiers:\n"
+ "\n"
+ " else false if true\n"
+ "\n"
+ "Integer literals\n"
+ "\n"
+ " An integer literal represents a decimal integer value.\n"
+ "\n"
+ " integer = [ \"-\" ] digit { digit } .\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 \"$\", `\"`, or newline */ .\n"
+ "\n"
+ " After a backslash, certain sequences represent special characters:\n"
+ "\n"
+ " \\\" U+0022 quotation mark\n"
+ " \\$ U+0024 dollar sign\n"
+ " \\\\ U+005C backslash\n"
+ "\n"
+ " All other backslashes represent themselves.\n"
+ "\n"
+ "Punctuation\n"
+ "\n"
+ " The following character sequences represent punctuation:\n"
+ "\n"
+ " + += == != ( )\n"
+ " - -= < <= [ ]\n"
+ " ! = > >= { }\n"
+ " && || . ,\n"
+ "\n"
+ "Grammar\n"
+ "\n"
+ " The input tokens form a syntax tree following a context-free grammar:\n"
+ "\n"
+ " 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"
+ " Expr = UnaryExpr | Expr BinaryOp Expr .\n"
+ " UnaryExpr = PrimaryExpr | UnaryOp UnaryExpr .\n"
+ " PrimaryExpr = identifier | integer | string | Call\n"
+ " | identifier \"[\" Expr \"]\"\n"
+ " | identifier \".\" identifier\n"
+ " | \"(\" Expr \")\"\n"
+ " | \"[\" [ ExprList [ \",\" ] ] \"]\" .\n"
+ " ExprList = Expr { \",\" Expr } .\n"
+ "\n"
+ " AssignOp = \"=\" | \"+=\" | \"-=\" .\n"
+ " UnaryOp = \"!\" .\n"
+ " BinaryOp = \"+\" | \"-\" // highest priority\n"
+ " | \"<\" | \"<=\" | \">\" | \">=\"\n"
+ " | \"==\" | \"!=\"\n"
+ " | \"&&\"\n"
+ " | \"||\" . // lowest priority\n"
+ "\n"
+ " All binary operators are left-associative.\n";
enum Precedence {
PRECEDENCE_ASSIGNMENT = 1, // Lowest precedence.
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