Remove an outdated test #148918
Merged
Remove an outdated test #148918
+17
−37
Conversation
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
rustbot
added
S-waiting-on-review
Collaborator
|
r? @davidtwco rustbot has assigned @davidtwco. Use |
jdonszelmann
requested changes
Nov 14, 2025
Contributor
There was a problem hiding this comment.
I've looked through the tests, and I can't find one (not even doc test) that tests the fact that try_from has a blanket impl for T: Into, etc. So maybe having some library test for that would be nice? This test on its own seems indeed useless though, since 1.41 definitely.
rustbot
added
S-waiting-on-author
This... is a weird test. It has two impls: - `impl<T> From<Foo<T>> for Box<T>` (commented out, more on that later), and - `impl<T> Into<Vec<T>> for Foo<T>` The idea of that test is to show that the first impl doesn't compile, but the second does, thus `TryFrom` should be using `Into` and not `From` (because `Into` is more general, since the `From` impl doesn't compile). However: 1. The types are different -- `Box` vs `Vec`, which is significant b/c `Box` is fundamental 2. The commented out impl actually compiles! (which wasn't detected b/c it's commented out :\ ) Here is a table for compilation of the impls: | | `Vec` | `Box` | |--------|--------------|----------------| | `From` | since 1.41.0 | never | | `Into` | always | not since 1.28 | [godbolt used to test this](https://godbolt.org/z/T38E3jGKa) Order of events: 1. in `1.28` the `incoherent_fundamental_impls` lint becomes deny by default (this is *not* mentioned in the changelog yay) 2. `1.32` changed absolutely nothing, even though this version is credited in the test 3. the test was added (I'm not exactly sure when) (see rust-lang#56796) 4. in `1.41` coherence was relaxed to allow `From`+`Vec` to compile To conclude: since `1.41` this test does nothing (and before that it was written in a way which did not detect this change). It looks to me like today (since `1.41`) we *could* bound `TryFrom` impl with `From` (but now it'd be a useless breaking change of course). Am I missing anything? Is there a useful version of this test that could be written?
WaffleLapkin
force-pushed
the
tryfromwhattttt
branch
from
b9c620e to
e645e51
Compare
Collaborator
|
This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed. Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers. |
Member
Author
|
@rustbot review |
rustbot
added
S-waiting-on-review
Contributor
|
@bors r+ rollup |
Collaborator
bors
added
S-waiting-on-bors
bors
added a commit
that referenced
this pull request
Dec 3, 2025
Rollup of 5 pull requests Successful merges: - #148918 (Remove an outdated test) - #149244 (Fix std::mem::drop rustdoc misleading statement) - #149532 (Rename supertrait item shadowing lints) - #149541 (Various never type test improvements) - #149590 (linker: Remove special case for `rust-lld` in `detect_self_contained_mingw`) r? `@ghost` `@rustbot` modify labels: rollup
rust-timer
added a commit
that referenced
this pull request
Dec 3, 2025
Rollup merge of #148918 - WaffleLapkin:tryfromwhattttt, r=jdonszelmann Remove an outdated test This... is a weird test. It has two impls: - `impl<T> From<Foo<T>> for Box<T>` (commented out, more on that later), and - `impl<T> Into<Vec<T>> for Foo<T>` The idea of that test is to show that the first impl doesn't compile, but the second does, thus `TryFrom` should be using `Into` and not `From` (because `Into` is more general, since the `From` impl doesn't compile). However: 1. The types are different -- `Box` vs `Vec`, which is significant b/c `Box` is fundamental 2. The commented out impl actually compiles! (which wasn't detected b/c it's commented out :\ ) Here is a table for compilation of the impls: | | `Vec` | `Box` | |--------|--------------|----------------| | `From` | since 1.41.0 | never | | `Into` | always | not since 1.28 | [godbolt used to test this](https://godbolt.org/z/T38E3jGKa) Order of events: 1. in `1.28` the `incoherent_fundamental_impls` lint becomes deny by default (this is *not* mentioned in the changelog yay) 2. `1.32` changed absolutely nothing, even though this version is credited in the test 3. the test was added (I'm not exactly sure when) (see #56796) 4. in `1.41` coherence was relaxed to allow `From`+`Vec` to compile To conclude: since `1.41` this test does nothing (and before that it was written in a way which did not detect this change). It looks to me like today (since `1.41`) we *could* bound `TryFrom` impl with `From` (but now it'd be a useless breaking change of course). Am I missing anything? Is there a useful version of this test that could be written?
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
5 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... is a weird test.
It has two impls:
impl<T> From<Foo<T>> for Box<T>(commented out, more on that later), andimpl<T> Into<Vec<T>> for Foo<T>The idea of that test is to show that the first impl doesn't compile, but the second does, thus
TryFromshould be usingIntoand notFrom(becauseIntois more general, since theFromimpl doesn't compile).However:
BoxvsVec, which is significant b/cBoxis fundamentalHere is a table for compilation of the impls:
VecBoxFromIntogodbolt used to test this
Order of events:
1.28theincoherent_fundamental_implslint becomes deny by default (this is not mentioned in the changelog yay)1.32changed absolutely nothing, even though this version is credited in the testTryFromblanket impl to useIntoinstead ofFrom#56796)1.41coherence was relaxed to allowFrom+Vecto compileTo conclude: since
1.41this test does nothing (and before that it was written in a way which did not detect this change). It looks to me like today (since1.41) we could boundTryFromimpl withFrom(but now it'd be a useless breaking change of course).Am I missing anything? Is there a useful version of this test that could be written?