berkus
/
kdl
mirror of https://github.com/kdl-org/kdl.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Disallow idents like '.1' to avoid footguns

This commit is contained in:
Tab Atkins-Bittner 2024-01-03 17:08:49 -08:00
parent de37e11a29
commit 24cd2141d3
1 changed files with 22 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
SPEC.md
View File

@ -298,18 +298,23 @@ composed of any [Unicode Scalar
Value](https://unicode.org/glossary/#unicode_scalar_value) other than
[non-initial characters](#non-initial-characters), followed by any number of
Unicode Scalar Values other than [non-identifier
characters](#non-identifier-characters), so long as this doesn't produce
something confusable for a [Number](#number). For example, both a
[Number](#number) and an Identifier can start with `-`, but when an Identifier
starts with `-` the second character cannot be a digit. This is precisely
specified in the [Full Grammar](#full-grammar) below.
characters](#non-identifier-characters).
A handful of patterns are disallowed, to avoid confusion with other values:
* idents that appear to start with a [Number](#number)
(like `1.0v2` or `-1em`)
or the "almost a number" pattern of a decimal point without a leading digit
(like `.1`)
* idents that are the language keywords (`true`, `false`, and `null`) without their leading `#`
Identifiers that match these patterns _MUST_ be treated as a syntax error;
such values can only be written as quoted or raw strings.
The precise details of the identifier syntax is specified in the [Full Grammar](#full-grammar) below.
Identifier Strings are terminated by [Whitespace](#whitespace) or
[Newlines](#newline).
The literal identifiers `true`, `false`, and `null` are illegal Identifier
Strings, and _MUST_ be treated as a syntax error.
#### Non-initial characters
The following characters cannot be the first character in an
@ -540,6 +545,11 @@ There are four syntaxes for Numbers: Decimal, Hexadecimal, Octal, and Binary.
* They may optionally include a decimal separator `.`, followed by more digits, which may again be separated by `_`.
* They may optionally be followed by `E` or `e`, an optional `-` or `+`, and more digits, to represent an exponent value.
Note that, similar to JSON and some other languages,
numbers without an integer digit (such as `.1`) are illegal.
They must be written with at least one integer digit, like `0.1`.
(These patterns are also disallowed from [Identifier Strings](#identifier-string), to avoid confusion.)
### Boolean
A boolean [Value](#value) is either the symbol `#true` or `#false`. These
@ -680,9 +690,10 @@ node-children := '{' nodes final-node? '}'
node-terminator := single-line-comment | newline | ';' | eof
identifier := string | bare-identifier
bare-identifier := (unambiguous-ident - boolean - 'null') | numberish-ident
unambiguous-ident := (identifier-char - digit - sign) identifier-char*
numberish-ident := sign ((identifier-char - digit) identifier-char*)?
bare-identifier := (unambiguous-ident - boolean - 'null') | numberish-ident | dotted-ident
unambiguous-ident := (identifier-char - digit - sign - '.') identifier-char*
numberish-ident := sign ((identifier-char - digit - '.') identifier-char*)?
dotted-ident := '.' ((identifier-char - digit) identifier-char*)?
identifier-char := unicode - line-space - [\\/(){};\[\]="#] - disallowed-literal-code-points
keyword := '#' (boolean | 'null')