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Document #[cfg(version(...))] #1828

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34 changes: 34 additions & 0 deletions src/conditional-compilation.md
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ ConfigurationPredicate ->
| ConfigurationAll
| ConfigurationAny
| ConfigurationNot
| ConfigurationVersion
| `true`
| `false`

Expand All @@ -23,6 +24,15 @@ ConfigurationAny ->
ConfigurationNot ->
`not` `(` ConfigurationPredicate `)`

ConfigurationVersion ->
`version` `(` `"` ConfigurationVersionLiteral `"` `)`
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@ehuss ehuss May 28, 2025 •
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Shouldn't this be:

Suggested change
`version` `(` `"` ConfigurationVersionLiteral `"` `)`
`version` `(` ( STRING_LITERAL | RAW_STRING_LITERAL ) `)`

and assuming it is, I would just delete the other grammar productions and describe the format of the string in cfg.predicate.version in plain English. Or, we can keep ConfigurationVersionLiteral if you want, but the text will still need to be updated to say that the string needs to conform to the format described by ConfigurationVersionLiteral.

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@est31 est31 May 29, 2025 •
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yeah I think STRING_LITERAL | RAW_STRING_LITERAL is fine.

This works

#[cfg(version(r"1.0"))] fn foo() {}

foo();

note that syntactically, we don't require string literals here, i.e. this doesn't give an error:

#[cfg(any())]
#[cfg(version(hello(world)))] fn foo() {}

#[cfg(any())]
#[cfg(version(123))] fn foo() {}

probably the same for all cfg syntaxes.


ConfigurationVersionLiteral ->
ConfigurationVersionPart `.` ConfigurationVersionPart (`.` ConfigurationVersionPart)?

ConfigurationVersionPart ->
(DEC_DIGIT)+

ConfigurationPredicateList ->
ConfigurationPredicate (`,` ConfigurationPredicate)* `,`?
```
Expand Down Expand Up @@ -55,6 +65,11 @@ r[cfg.predicate.not]
r[cfg.predicate.literal]
* `true` or `false` literals, which are always true or false respectively.

r[cfg.predicate.version]
* `version()` with a version number inside. It is true if the language version
Comment on lines +68 to +69
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Can we merge cfg.version into this section so that it isn't described in two places?

the compiler targets is higher or equal to the contained version number.
It is false otherwise.
Comment on lines +68 to +71

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r[cfg.option-spec]
_Configuration options_ are either names or key-value pairs, and are either set or unset.

Expand Down Expand Up @@ -299,6 +314,19 @@ r[cfg.proc_macro]
Set when the crate being compiled is being compiled with the `proc_macro`
[crate type].

r[cfg.version]
### `version()`

r[cfg.version.behavior]
The `version()` predicate evaluates to true if both:

* The version number contained inside follows the format and
* The version number contained inside is less than or equal to the version
of the language the compiler targets.

r[cfg.version.format]
In order for it to be considered of valid format, the version number has to follow either the `"a.b.c"` scheme or the `"a.b"` scheme. Semantically, assume `c` to be 0 if not present. Order wise, version numbers behave as if they were Rust tuples of type `(u16, u16, u16)`.

r[cfg.panic]
### `panic`

Expand Down Expand Up @@ -371,6 +399,12 @@ fn needs_not_foo() {
// ...
}

// This function is only included if the language version is at least 1.50.0
#[cfg(version("1.50.0"))]
fn needs_new_compiler() {
// ...
}

// This function is only included when the panic strategy is set to unwind
#[cfg(panic = "unwind")]
fn when_unwinding() {
Expand Down
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