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just/GRAMMAR.md
2024-10-10 19:45:50 +00:00

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justfile grammar
================
Justfiles are processed by a mildly context-sensitive tokenizer
and a recursive descent parser. The grammar is LL(k), for an
unknown but hopefully reasonable value of k.
tokens
------
```
BACKTICK = `[^`]*`
INDENTED_BACKTICK = ```[^(```)]*```
COMMENT = #([^!].*)?$
DEDENT = emitted when indentation decreases
EOF = emitted at the end of the file
INDENT = emitted when indentation increases
LINE = emitted before a recipe line
NAME = [a-zA-Z_][a-zA-Z0-9_-]*
NEWLINE = \n|\r\n
RAW_STRING = '[^']*'
INDENTED_RAW_STRING = '''[^(''')]*'''
STRING = "[^"]*" # also processes \n \r \t \" \\ escapes
INDENTED_STRING = """[^(""")]*""" # also processes \n \r \t \" \\ escapes
LINE_PREFIX = @-|-@|@|-
TEXT = recipe text, only matches in a recipe body
```
grammar syntax
--------------
```
| alternation
() grouping
_? option (0 or 1 times)
_* repetition (0 or more times)
_+ repetition (1 or more times)
```
grammar
-------
```
justfile : item* EOF
item : alias
| assignment
| eol
| export
| import
| module
| recipe
| set
eol : NEWLINE
| COMMENT NEWLINE
alias : 'alias' NAME ':=' NAME eol
assignment : NAME ':=' expression eol
export : 'export' assignment
set : 'set' setting eol
setting : 'allow-duplicate-recipes' boolean?
| 'allow-duplicate-variables' boolean?
| 'dotenv-filename' ':=' string
| 'dotenv-load' boolean?
| 'dotenv-path' ':=' string
| 'dotenv-required' boolean?
| 'export' boolean?
| 'fallback' boolean?
| 'ignore-comments' boolean?
| 'positional-arguments' boolean?
| 'script-interpreter' ':=' string_list
| 'quiet' boolean?
| 'shell' ':=' string_list
| 'tempdir' ':=' string
| 'unstable' boolean?
| 'windows-powershell' boolean?
| 'windows-shell' ':=' string_list
| 'working-directory' ':=' string
boolean : ':=' ('true' | 'false')
string_list : '[' string (',' string)* ','? ']'
import : 'import' '?'? string? eol
module : 'mod' '?'? NAME string? eol
expression : 'if' condition '{' expression '}' 'else' '{' expression '}'
| 'assert' '(' condition ',' expression ')'
| '/' expression
| value '/' expression
| value '+' expression
| value
condition : expression '==' expression
| expression '!=' expression
| expression '=~' expression
value : NAME '(' sequence? ')'
| BACKTICK
| INDENTED_BACKTICK
| NAME
| string
| '(' expression ')'
string : 'x'? STRING
| 'x'? INDENTED_STRING
| 'x'? RAW_STRING
| 'x'? INDENTED_RAW_STRING
sequence : expression ',' sequence
| expression ','?
recipe : attributes* '@'? NAME parameter* variadic? ':' dependencies eol body?
attributes : '[' attribute* ']' eol
attribute : NAME ( '(' string ')' )?
parameter : '$'? NAME
| '$'? NAME '=' value
variadic : '*' parameter
| '+' parameter
dependencies : dependency* ('&&' dependency+)?
dependency : NAME
| '(' NAME expression* ')'
body : INDENT line+ DEDENT
line : LINE LINE_PREFIX? (TEXT | interpolation)+ NEWLINE
| NEWLINE
interpolation : '{{' expression '}}'
```