Add explanation for E0756 #76489

GuillaumeGomez · 2020-09-08T19:02:50Z

pickfire

Oh, I thought #[ffi_const] was somehow related to const fn but it wasn't.

pickfire · 2020-09-09T00:26:30Z

compiler/rustc_error_codes/src/error_codes/E0756.md

+extern "C" {
+    #[ffi_const] // ok!
+    pub fn strlen(s: *const i8) -> i32;
+}


Same suggestion here. Show another method (or maybe a better one) with less contrast, no need to remove the current one.

#[ffi_pure] extern "C" pub fn foo() {}

jyn514 · 2020-09-09T02:23:51Z

compiler/rustc_error_codes/src/error_codes/E0756.md

@@ -0,0 +1,29 @@
+The `ffi_const` attribute was used on something else than a foreign function


Suggested change

The `ffi_const` attribute was used on something else than a foreign function

The `ffi_const` attribute was used on something other than a foreign function

jyn514 · 2020-09-09T02:24:23Z

compiler/rustc_error_codes/src/error_codes/E0756.md

+```
+
+The `ffi_const` attribute can only be used on foreign function declarations
+which have no effects except for their return value:


Let's not confuse people into thinking about effect type systems ;)

Suggested change

which have no effects except for their return value:

which have no side effects except for their return value:

Previously I was suggesting

The `ffi_pure` attribute can only be used on foreign functions which do not have side effects or infinite loops:

which could be used exactly the same here, I wonder if that is better since I combined multiple parts from the book.

C assumes that all functions don't have infinite loops; it's called "forward progress guarantee". The rules around it are somewhat odd and I don't think they belong here, see https://blog.rust-lang.org/inside-rust/2020/03/19/terminating-rust.html for details.

jonas-schievink · 2020-09-13T16:10:55Z

r? @jyn514

GuillaumeGomez · 2020-09-21T11:39:27Z

@bors: r=jyn514 rollup

bors · 2020-09-21T11:39:29Z

📌 Commit f72fc26cddb9255aa8a7fb12107fc41abe27879f has been approved by jyn514

Rollup of 10 pull requests Successful merges: - rust-lang#76439 (Add error explanation for E0755) - rust-lang#76521 (Fix segfault if pthread_getattr_np fails) - rust-lang#76835 (make replace_prefix only take &str as arguments ) - rust-lang#76967 (Revert adding Atomic::from_mut.) - rust-lang#76977 (Add a regression test for copy propagation miscompilation) - rust-lang#76981 (liballoc bench use imported path Bencher) - rust-lang#76983 (BTreeMap: extra testing & fixed comments) - rust-lang#76996 (Fix typo in rustc_lexer docs) - rust-lang#77009 (Dogfood total_cmp in the test crate) - rust-lang#77012 (update Miri for another bugfix) Failed merges: - rust-lang#76489 (Add explanation for E0756) r? `@ghost`

bors · 2020-09-21T17:52:16Z

☔ The latest upstream changes (presumably #77013) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

jyn514 · 2020-09-21T17:57:32Z

Merged in #77013, not sure why github didn't notice.

GuillaumeGomez · 2020-09-21T18:36:40Z

No, it was E0755, not this one. ;)

GuillaumeGomez · 2020-09-21T19:05:47Z

Let's go again!

@bors: r=jyn514 rollup

bors · 2020-09-21T19:05:50Z

📌 Commit 63195ec has been approved by jyn514

@pickfire

…6, r=jyn514 Add explanation for E0756 r? @pickfire

@pickfire

…6, r=jyn514 Add explanation for E0756 r? @pickfire

…atic-morse Rollup of 13 pull requests Successful merges: - rust-lang#72734 (Reduce duplicate in liballoc reserve error handling) - rust-lang#76131 (Don't use `zip` to compare iterators during pretty-print hack) - rust-lang#76150 (Don't recommend ManuallyDrop to customize drop order) - rust-lang#76275 (Implementation of Write for some immutable ref structs) - rust-lang#76489 (Add explanation for E0756) - rust-lang#76581 (do not ICE on bound variables, return `TooGeneric` instead) - rust-lang#76655 (Make some methods of `Pin` unstable const) - rust-lang#76783 (Only get ImplKind::Impl once) - rust-lang#76807 (Use const-checking to forbid use of unstable features in const-stable functions) - rust-lang#76888 (use if let instead of single match arm expressions) - rust-lang#76914 (extend `Ty` and `TyCtxt` lints to self types) - rust-lang#77022 (Reduce boilerplate for BytePos and CharPos) - rust-lang#77032 (lint missing docs for extern items) Failed merges: r? `@ghost`

GuillaumeGomez force-pushed the add-explanation-e0756 branch from b76f40f to d5a1765 Compare September 8, 2020 19:12

pickfire reviewed Sep 9, 2020

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jyn514 added the A-error-codes Area: Explanation of an error code (--explain) label Sep 9, 2020

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jyn514 added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. A-FFI Area: Foreign function interface (FFI) labels Sep 9, 2020

rust-highfive assigned jyn514 Sep 13, 2020

GuillaumeGomez force-pushed the add-explanation-e0756 branch from d5a1765 to f72fc26 Compare September 21, 2020 11:39

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 21, 2020

RalfJung mentioned this pull request Sep 21, 2020

Rollup of 10 pull requests #77013

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 21, 2020

jyn514 closed this Sep 21, 2020

GuillaumeGomez reopened this Sep 21, 2020

Add explanation for E0756

63195ec

GuillaumeGomez force-pushed the add-explanation-e0756 branch from f72fc26 to 63195ec Compare September 21, 2020 19:05

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 21, 2020

Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Sep 22, 2020

Rollup merge of rust-lang#76489 - GuillaumeGomez:add-explanation-e075…

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…6, r=jyn514 Add explanation for E0756 r? @pickfire

Dylan-DPC-zz mentioned this pull request Sep 22, 2020

Rollup of 13 pull requests #77038

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ecstatic-morse mentioned this pull request Sep 22, 2020

Rollup of 13 pull requests #77039

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ecstatic-morse added a commit to ecstatic-morse/rust that referenced this pull request Sep 22, 2020

Rollup merge of rust-lang#76489 - GuillaumeGomez:add-explanation-e075…

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…6, r=jyn514 Add explanation for E0756 r? @pickfire

ecstatic-morse mentioned this pull request Sep 22, 2020

Rollup of 13 pull requests #77040

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bors merged commit ef6c3a7 into rust-lang:master Sep 22, 2020

rustbot added this to the 1.48.0 milestone Sep 22, 2020

pickfire mentioned this pull request Sep 22, 2020

Add alternative extern syntax #77045

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GuillaumeGomez deleted the add-explanation-e0756 branch September 22, 2020 07:42

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Add explanation for E0756 #76489

Add explanation for E0756 #76489

GuillaumeGomez commented Sep 8, 2020

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GuillaumeGomez commented Sep 21, 2020

bors commented Sep 21, 2020

		@@ -0,0 +1,29 @@
		The `ffi_const` attribute was used on something else than a foreign function

	which have no effects except for their return value:
	which have no side effects except for their return value:

Add explanation for E0756 #76489

Add explanation for E0756 #76489

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