Improve E0512 error message

[GuillaumeGomez]

cc @nagisa

[rust-highfive]

r? @arielb1

(rust_highfive has picked a reviewer for you, use r? to override)

[nagisa]

Reading now, I’d remove the “two” actually, I think, since that’s implied both by the function signature and list of types that come after the colon.

[nagisa]

Looks like an improvement to me.

[GuillaumeGomez]

Updated !

#28909

[pnkfelix]

@GuillaumeGomez why did you drop the word "potentially" ? Do you think it unnecessary?

[GuillaumeGomez]

Then it would be a "potential" error, no? If the types did have the same size, either we'd have another error or it'd be just fine. I don't see other possibility here.

[pnkfelix]

(I resolved my question with @GuillaumeGomez ; i had overlooked that this message is solely coming from trans, not the earlier type-checking where the sizes can be unknown.)

[pnkfelix]

@bors r+

[pnkfelix]

@bors r+

[bors]

📌 Commit 35f8184 has been approved by pnkfelix

[bors]

⌛ Testing commit 35f8184 with merge 40a1e4f...

[bors]

💔 Test failed - auto-mac-64-opt

[Manishearth]

failures:

---- [compile-fail] compile-fail/packed-struct-generic-transmute.rs stdout ----

error: error pattern ' transmute called on types with different size' not found!
status: exit code: 101
command: x86_64-apple-darwin/stage2/bin/rustc /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs -L x86_64-apple-darwin/test/compile-fail/ --target=x86_64-apple-darwin -L x86_64-apple-darwin/test/compile-fail/packed-struct-generic-transmute.stage2-x86_64-apple-darwin.compile-fail.libaux -C prefer-dynamic -o x86_64-apple-darwin/test/compile-fail/packed-struct-generic-transmute.stage2-x86_64-apple-darwin --cfg rtopt -O -L x86_64-apple-darwin/rt
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:22:5: 22:11 warning: struct field is never used: `bar`, #[warn(dead_code)] on by default
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:22     bar: T,
                                                                                                                               ^~~~~~
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:23:5: 23:11 warning: struct field is never used: `baz`, #[warn(dead_code)] on by default
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:23     baz: S
                                                                                                                               ^~~~~~
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:34:38: 34:52 error: transmute called with differently sized types: Foo<[u8; 5], i32> (72 bits) to Oof<[u8; 5], i32> (96 bits) [E0512]
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-generic-transmute.rs:34         let oof: Oof<[u8; 5], i32> = mem::transmute(foo);
                                                                                                                                                                ^~~~~~~~~~~~~~
error: aborting due to previous error

------------------------------------------

thread '[compile-fail] compile-fail/packed-struct-generic-transmute.rs' panicked at 'explicit panic', /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/compiletest/runtest.rs:1501

---- [compile-fail] compile-fail/packed-struct-transmute.rs stdout ----

error: error pattern ' transmute called on types with different size' not found!
status: exit code: 101
command: x86_64-apple-darwin/stage2/bin/rustc /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs -L x86_64-apple-darwin/test/compile-fail/ --target=x86_64-apple-darwin -L x86_64-apple-darwin/test/compile-fail/packed-struct-transmute.stage2-x86_64-apple-darwin.compile-fail.libaux -C prefer-dynamic -o x86_64-apple-darwin/test/compile-fail/packed-struct-transmute.stage2-x86_64-apple-darwin --cfg rtopt -O -L x86_64-apple-darwin/rt
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:22:5: 22:12 warning: struct field is never used: `bar`, #[warn(dead_code)] on by default
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:22     bar: u8,
                                                                                                                       ^~~~~~~
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:23:5: 23:15 warning: struct field is never used: `baz`, #[warn(dead_code)] on by default
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:23     baz: usize
                                                                                                                       ^~~~~~~~~~
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:35:24: 35:38 error: transmute called with differently sized types: Foo (72 bits) to Oof (128 bits) [E0512]
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/packed-struct-transmute.rs:35         let oof: Oof = mem::transmute(foo);
                                                                                                                                          ^~~~~~~~~~~~~~
error: aborting due to previous error

------------------------------------------

thread '[compile-fail] compile-fail/packed-struct-transmute.rs' panicked at 'explicit panic', /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/compiletest/runtest.rs:1501

---- [compile-fail] compile-fail/transmute-different-sizes.rs stdout ----

error: unexpected compiler error or warning: '/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs:18:17: 18:26 error: transmute called with differently sized types: i16 (16 bits) to i8 (8 bits) [E0512]'
status: exit code: 101
command: x86_64-apple-darwin/stage2/bin/rustc /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs -L x86_64-apple-darwin/test/compile-fail/ --target=x86_64-apple-darwin -L x86_64-apple-darwin/test/compile-fail/transmute-different-sizes.stage2-x86_64-apple-darwin.compile-fail.libaux -C prefer-dynamic -o x86_64-apple-darwin/test/compile-fail/transmute-different-sizes.stage2-x86_64-apple-darwin --cfg rtopt -O -L x86_64-apple-darwin/rt
stdout:
------------------------------------------

------------------------------------------
stderr:
------------------------------------------
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs:18:17: 18:26 error: transmute called with differently sized types: i16 (16 bits) to i8 (8 bits) [E0512]
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs:18     let _: i8 = transmute(16i16);
                                                                                                                                     ^~~~~~~~~
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs:23:17: 23:26 error: transmute called with differently sized types: &T (could be 64 bits) to i8 (could be 8 bits) [E0512]
/Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/test/compile-fail/transmute-different-sizes.rs:23     let _: i8 = transmute(x);
                                                                                                                                     ^~~~~~~~~
error: aborting due to 2 previous errors

------------------------------------------

thread '[compile-fail] compile-fail/transmute-different-sizes.rs' panicked at 'explicit panic', /Users/rustbuild/src/rust-buildbot/slave/auto-mac-64-opt/build/src/compiletest/runtest.rs:1501


failures:
    [compile-fail] compile-fail/packed-struct-generic-transmute.rs
    [compile-fail] compile-fail/packed-struct-transmute.rs
    [compile-fail] compile-fail/transmute-different-sizes.rs

[GuillaumeGomez]

@Manishearth: I'm still wondering what happened. I'm thinking about the error comment which could be invalid but it doesn't seem to...

[Manishearth]

Those tests use error-pattern, which puts a pattern at the top of the file. You need to fix those patterns to match the new error message.

[Manishearth]

@bors r+

[bors]

📌 Commit a3f9fc6 has been approved by Manishearth

[bors]

⌛ Testing commit a3f9fc6 with merge beeaea4...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt