Qualify constness in rvalue expressions for promotion to globals.#21744
Merged
bors merged 15 commits intorust-lang:masterfrom Feb 16, 2015
Merged
Qualify constness in rvalue expressions for promotion to globals.#21744bors merged 15 commits intorust-lang:masterfrom
bors merged 15 commits intorust-lang:masterfrom
Conversation
Member
Author
Contributor
|
r? @nick29581 (rust_highfive has picked a reviewer for you, use r? to override) |
Collaborator
|
⌛ Testing commit acb37ce with merge f3f47ad... |
Member
Author
Collaborator
|
💔 Test failed - auto-win-32-nopt-t |
eddyb
force-pushed
the
rvalue-promotion
branch
from
acb37ce to
91d51c8
Compare
Member
Author
|
@bors try 91d51c8 |
Collaborator
|
⌛ Testing commit 91d51c8 with merge c41f7b6... |
Collaborator
|
💔 Test failed - auto-mac-64-opt |
eddyb
force-pushed
the
rvalue-promotion
branch
from
91d51c8 to
f9556d8
Compare
Member
Author
|
@bors try f9556d8 |
Collaborator
|
⌛ Testing commit f9556d8 with merge 70b6649... |
Collaborator
|
💔 Test failed - auto-mac-64-nopt-t |
Contributor
|
This looks great: r+ I have some nits and minor comments, which you can find as comments in this commit: nikomatsakis@feb8ca7 |
Member
Author
|
Blocked on #21996. |
eddyb
force-pushed
the
rvalue-promotion
branch
from
f9556d8 to
a091c5a
Compare
Member
Author
|
@bors r=nikomatsakis a091c5a |
Collaborator
|
⌛ Testing commit a091c5a with merge 5fcfa12... |
Collaborator
|
💔 Test failed - auto-mac-32-opt |
Collaborator
|
💔 Test failed - auto-linux-64-nopt-t |
…ypes with [u8; 0].
eddyb
force-pushed
the
rvalue-promotion
branch
from
7e45074 to
b49f528
Compare
Member
Author
Collaborator
bors
added a commit
that referenced
this pull request
Feb 16, 2015
This includes everything necessary for promoting borrows of constant rvalues to `'static`. That is, `&expr` will have the type `&'static T` if `const T: &'static T = &expr;` is valid. There is a small exception, dereferences of raw pointers, as they misbehave. They still "work" in constants as I didn't want to break legitimate uses (are there any?). The qualification done here can be expanded to allow simple CTFE via `const fn`.
Collaborator
Contributor
|
Isn't this designed to make |
Contributor
|
Epic fight with @bors! |
Contributor
|
(If tests are added, they can close rust-lang/rfcs#827.) |
Member
Author
|
@huonw No, that part needs an RFC. @nikomatsakis wanted to write one for the longest time - in any case, there's a few different directions to go from this base implementation. |
Dylan-DPC-zz
pushed a commit
to Dylan-DPC-zz/rust
that referenced
this pull request
Sep 7, 2020
Do not promote &mut of a non-ZST ever
Since ~pre-1.0~ 1.36, we have accepted code like this:
```rust
static mut TEST: &'static mut [i32] = {
let x = &mut [1,2,3];
x
};
```
I tracked it back to rust-lang#21744, but unfortunately could not find any discussion or RFC that would explain why we thought this was a good idea. And it's not, it breaks all sorts of things -- see rust-lang#75556.
To fix rust-lang#75556, we have to stop promoting non-ZST mutable references no matter the context, which is what this PR does. It's a breaking change.
Notice that this still works, since it does not rely on promotion:
```rust
static mut TEST: &'static mut [i32] = &mut [0,1,2];
```
Cc @rust-lang/wg-const-eval
bors
added a commit
to rust-lang-ci/rust
that referenced
this pull request
Sep 8, 2020
Do not promote &mut of a non-ZST ever
Since ~pre-1.0~ 1.36, we have accepted code like this:
```rust
static mut TEST: &'static mut [i32] = {
let x = &mut [1,2,3];
x
};
```
I tracked it back to rust-lang#21744, but unfortunately could not find any discussion or RFC that would explain why we thought this was a good idea. And it's not, it breaks all sorts of things -- see rust-lang#75556.
To fix rust-lang#75556, we have to stop promoting non-ZST mutable references no matter the context, which is what this PR does. It's a breaking change.
Notice that this still works, since it does not rely on promotion:
```rust
static mut TEST: &'static mut [i32] = &mut [0,1,2];
```
Cc `@rust-lang/wg-const-eval`
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
7 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
This includes everything necessary for promoting borrows of constant rvalues to
'static.That is,
&exprwill have the type&'static Tifconst T: &'static T = &expr;is valid.There is a small exception, dereferences of raw pointers, as they misbehave.
They still "work" in constants as I didn't want to break legitimate uses (are there any?).
The qualification done here can be expanded to allow simple CTFE via
const fn.