just/GRAMMAR.md
Casey Rodarmor aefdcea7d0
Gargantuan refactor (#522)
- Instead of changing the current directory with `env::set_current_dir`
  to be implicitly inherited by subprocesses, we now use
  `Command::current_dir` to set it explicitly. This feels much better,
  since we aren't dependent on the implicit state of the process's
  current directory.

- Subcommand execution is much improved.

- Added a ton of tests for config parsing, config execution, working
  dir, and search dir.

- Error messages are improved. Many more will be colored.

- The Config is now onwed, instead of borrowing from the arguments and
  the `clap::ArgMatches` object. This is a huge ergonomic improvement,
  especially in tests, and I don't think anyone will notice.

- `--edit` now uses `$VISUAL`, `$EDITOR`, or `vim`, in that order,
  matching git, which I think is what most people will expect.

- Added a cute `tmptree!{}` macro, for creating temporary directories
  populated with directories and files for tests.

- Admitted that grammer is LL(k) and I don't know what `k` is.
2019-11-09 21:43:20 -08:00

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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 = `[^`\n\r]*`
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 = '[^'\r\n]*'
STRING = "[^"]*" # also processes \n \r \t \" \\ escapes
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 : recipe
| alias
| assignment
| export
| eol
eol : NEWLINE
| COMMENT NEWLINE
alias : 'alias' NAME ':=' NAME
assignment : NAME ':=' expression eol
export : 'export' assignment
expression : value '+' expression
| value
value : NAME '(' sequence? ')'
| STRING
| RAW_STRING
| BACKTICK
| NAME
| '(' expression ')'
sequence : expression ',' sequence
| expression ','?
recipe : '@'? NAME parameter* ('+' parameter)? ':' dependencies? body?
parameter : NAME
| NAME '=' value
dependencies : NAME+
body : INDENT line+ DEDENT
line : LINE (TEXT | interpolation)+ NEWLINE
| NEWLINE
interpolation : '{{' expression '}}'
```