Merge pull request #1603 from compiler-errors/patch-1

Raw lifetimes

Author: ehuss

src/identifiers.md

@@ -14,6 +14,8 @@ r[ident.syntax]
 >
 > IDENTIFIER :\
 > NON_KEYWORD_IDENTIFIER | RAW_IDENTIFIER
+>
+> RESERVED_RAW_IDENTIFIER : `r#_`
 
 <!-- When updating the version, update the UAX links, too. -->
 r[ident.unicode]
@@ -71,6 +73,10 @@ r[ident.raw.allowed]
 Unlike a normal identifier, a raw identifier may be any strict or reserved
 keyword except the ones listed above for `RAW_IDENTIFIER`.
 
+r[ident.raw.reserved]
+It is an error to use the RESERVED_RAW_IDENTIFIER token `r#_` in order to avoid confusion with the [_WildcardPattern_].
+
+[_WildcardPattern_]: patterns.md#wildcard-pattern
 [`extern crate`]: items/extern-crates.md
 [`no_mangle`]: abi.md#the-no_mangle-attribute
 [`path` attribute]: items/modules.md#the-path-attribute

src/tokens.md

@@ -758,17 +758,39 @@ r[lex.token.life.syntax]
 >       `'` [IDENTIFIER_OR_KEYWORD][identifier]
 >   _(not immediately followed by `'`)_\
 >    | `'_`
->   _(not immediately followed by `'`)_
+>   _(not immediately followed by `'`)_\
+>    | RAW_LIFETIME
 >
 > LIFETIME_OR_LABEL :\
 >       `'` [NON_KEYWORD_IDENTIFIER][identifier]
+>   _(not immediately followed by `'`)_\
+>    | RAW_LIFETIME
+>
+> RAW_LIFETIME :\
+> &nbsp;&nbsp; `'r#` [IDENTIFIER_OR_KEYWORD][identifier] <sub>*Except `crate`, `self`, `super`, `Self`*</sub>
+>   _(not immediately followed by `'`)_
+>
+> RESERVED_RAW_LIFETIME : `'r#_`
 >   _(not immediately followed by `'`)_
 
 r[lex.token.life.intro]
 Lifetime parameters and [loop labels] use LIFETIME_OR_LABEL tokens. Any
 LIFETIME_TOKEN will be accepted by the lexer, and for example, can be used in
 macros.
 
+r[lex.token.life.raw.intro]
+A raw lifetime is like a normal lifetime, but its identifier is prefixed by `r#`. (Note that the `r#` prefix is not included as part of the actual lifetime.)
+
+r[lex.token.life.raw.allowed]
+Unlike a normal lifetime, a raw lifetime may be any strict or reserved keyword except the ones listed above for `RAW_LIFETIME`.
+
+r[lex.token.life.raw.reserved]
+It is an error to use the RESERVED_RAW_LIFETIME token `'r#_` in order to avoid confusion with the [placeholder lifetime].
+
+r[lex.token.life.raw.edition2021]
+> **Edition differences**: Raw lifetimes are accepted in the 2021
+> edition or later. In earlier additions the token `'r#lt` is lexed as `'r # lt`.
+
 ## Punctuation
 
 r[lex.token.punct]
@@ -849,7 +871,8 @@ r[lex.token.reserved-prefix.syntax]
 > **<sup>Lexer 2021+</sup>**\
 > RESERVED_TOKEN_DOUBLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b` or `c` or `r` or `br` or `cr`_</sub> | `_` ) `"`\
 > RESERVED_TOKEN_SINGLE_QUOTE : ( IDENTIFIER_OR_KEYWORD <sub>_Except `b`_</sub> | `_` ) `'`\
-> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br` or `cr`_</sub> | `_` ) `#`
+> RESERVED_TOKEN_POUND : ( IDENTIFIER_OR_KEYWORD <sub>_Except `r` or `br` or `cr`_</sub> | `_` ) `#`\
+> RESERVED_TOKEN_LIFETIME : `'` (IDENTIFIER_OR_KEYWORD <sub>_Except `r`_</sub> | _) `#`
 
 r[lex.token.reserved-prefix.intro]
 Some lexical forms known as _reserved prefixes_ are reserved for future use.
@@ -863,6 +886,9 @@ Note that raw identifiers, raw string literals, and raw byte string literals may
 r[lex.token.reserved-prefix.strings]
 Similarly the `r`, `b`, `br`, `c`, and `cr` prefixes used in raw string literals, byte literals, byte string literals, raw byte string literals, C string literals, and raw C string literals are not interpreted as reserved prefixes.
 
+r[lex.token.reserved-prefix.life]
+Source input which would otherwise be lexically interpreted as a non-raw lifetime (or a keyword or `_`) which is immediately followed by a `#` character (without intervening whitespace) is identified as a reserved lifetime prefix.
+
 r[lex.token.reserved-prefix.edition2021]
 > **Edition differences**: Starting with the 2021 edition, reserved prefixes are reported as an error by the lexer (in particular, they cannot be passed to macros).
 >
@@ -875,6 +901,7 @@ r[lex.token.reserved-prefix.edition2021]
 > lexes!{continue 'foo}
 > lexes!{match "..." {}}
 > lexes!{r#let#foo}         // three tokens: r#let # foo
+> lexes!{'prefix #lt}
 > ```
 >
 > Examples accepted before the 2021 edition but rejected later:
@@ -883,6 +910,7 @@ r[lex.token.reserved-prefix.edition2021]
 > lexes!{a#foo}
 > lexes!{continue'foo}
 > lexes!{match"..." {}}
+> lexes!{'prefix#lt}
 > ```
 
 [Inferred types]: types/inferred.md
@@ -924,6 +952,7 @@ r[lex.token.reserved-prefix.edition2021]
 [numeric types]: types/numeric.md
 [paths]: paths.md
 [patterns]: patterns.md
+[placeholder lifetime]: lifetime-elision.md
 [question]: expressions/operator-expr.md#the-question-mark-operator
 [range]: expressions/range-expr.md
 [rangepat]: patterns.md#range-patterns