Detect cases where `?` is applied on a type that could be coming from a different crate version than expected #150558

estebank · 2025-12-31T23:41:11Z

error[E0277]: `?` couldn't convert the error to `dependency::Error`
  --> replaced
   |
LL | fn main() -> Result<(), Error> {
   |              ----------------- expected `dependency::Error` because of this
...
LL |     Err(Error2)?;
   |     -----------^ the trait `From<Error2>` is not implemented for `dependency::Error`
   |     |
   |     this can't be annotated with `?` because it has type `Result<_, Error2>`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
help: the trait `From<Error2>` is not implemented for `dependency::Error`
      but trait `From<()>` is implemented for it
  --> replaced
   |
LL | impl From<()> for Error {
   | ^^^^^^^^^^^^^^^^^^^^^^^
   = help: for that trait implementation, expected `()`, found `Error2`
   = note: there are multiple different versions of crate `dependency` in the dependency graph
   = help: you can use `cargo tree` to explore your dependency tree

The existing checks rely on having access to the actual types/traits that diverged to detect they are called the same, come from different crates with the same name. The new check is less specific, merely looking to see if the crate name the involved type belongs has multiple crates.

CC #78552.

… a different crate version than expected ``` error[E0277]: `?` couldn't convert the error to `dependency::Error` --> replaced | LL | fn main() -> Result<(), Error> { | ----------------- expected `dependency::Error` because of this ... LL | Err(Error2)?; | -----------^ the trait `From<Error2>` is not implemented for `dependency::Error` | | | this can't be annotated with `?` because it has type `Result<_, Error2>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait help: the trait `From<Error2>` is not implemented for `dependency::Error` but trait `From<()>` is implemented for it --> replaced | LL | impl From<()> for Error { | ^^^^^^^^^^^^^^^^^^^^^^^ = help: for that trait implementation, expected `()`, found `Error2` = note: there are multiple different versions of crate `dependency` in the dependency graph = help: you can use `cargo tree` to explore your dependency tree ``` The existing checks rely on having access to the actual types/traits that diverged to detect they are called the same, come from different crates with the same name. The new check is less specific, merely looking to see if the crate name the involved type belongs has multiple crates.

rustbot · 2025-12-31T23:41:16Z

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rustbot · 2025-12-31T23:41:17Z

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estebank · 2026-01-02T20:38:02Z

This is the output I get:

~/workspace/rust-issue-78552-repro/repro-runtime$ cargo +dev build
   Compiling repro-runtime v0.1.0 (/home/gh-estebank/workspace/rust-issue-78552-repro/repro-runtime)
error[E0277]: `?` couldn't convert the error to `Status`
   --> repro-runtime/src/main.rs:5:78
    |
  4 | fn main() -> Result<(), Status> {
    |              ------------------ expected `Status` because of this
  5 |     Err(ApplicationError::ImpossibleCondition("you tried to run it!".into()))?
    |     -------------------------------------------------------------------------^ the trait `From<ApplicationError>` is not implemented for `Status`
    |     |
    |     this can't be annotated with `?` because it has type `Result<_, ApplicationError>`
    |
    = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
help: the following other types implement trait `From<T>`
   --> /home/gh-estebank/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/tonic-0.14.2/src/status.rs:709:1
    |
709 | impl From<h2::Error> for Status {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Status` implements `From<h2::error::Error>`
...
722 | impl From<std::io::Error> for Status {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Status` implements `From<std::io::Error>`
    = note: there are multiple different versions of crate `tonic` in the dependency graph
    = help: you can use `cargo tree` to explore your dependency tree

For more information about this error, try `rustc --explain E0277`.
error: could not compile `repro-runtime` (bin "repro-runtime") due to 1 previous error

jieyouxu

Thanks

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jieyouxu · 2026-01-03T06:23:38Z

@bors r+ rollup

bors · 2026-01-03T06:23:40Z

📌 Commit 22bb4fe has been approved by jieyouxu

It is now in the queue for this repository.

…jieyouxu Detect cases where `?` is applied on a type that could be coming from a different crate version than expected ``` error[E0277]: `?` couldn't convert the error to `dependency::Error` --> replaced | LL | fn main() -> Result<(), Error> { | ----------------- expected `dependency::Error` because of this ... LL | Err(Error2)?; | -----------^ the trait `From<Error2>` is not implemented for `dependency::Error` | | | this can't be annotated with `?` because it has type `Result<_, Error2>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait help: the trait `From<Error2>` is not implemented for `dependency::Error` but trait `From<()>` is implemented for it --> replaced | LL | impl From<()> for Error { | ^^^^^^^^^^^^^^^^^^^^^^^ = help: for that trait implementation, expected `()`, found `Error2` = note: there are multiple different versions of crate `dependency` in the dependency graph = help: you can use `cargo tree` to explore your dependency tree ``` The existing checks rely on having access to the actual types/traits that diverged to detect they are called the same, come from different crates with the same name. The new check is less specific, merely looking to see if the crate name the involved type belongs has multiple crates. CC rust-lang#78552.

Rollup of 5 pull requests Successful merges: - #150558 (Detect cases where `?` is applied on a type that could be coming from a different crate version than expected) - #150570 (Removed confusing diagnostics note for trait required for `?` operator use) - #150589 (Remove unneeded `forbid_generic` field from `Res::SelfTyAlias`) - #150635 (triagebot: Add a mention for `dec2flt`, `flt2dec`, and `fmt/num.rs`) - #150637 (Fix broken edit links in Unstable and rustc books) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #150558 - estebank:multiple-dep-versions, r=jieyouxu Detect cases where `?` is applied on a type that could be coming from a different crate version than expected ``` error[E0277]: `?` couldn't convert the error to `dependency::Error` --> replaced | LL | fn main() -> Result<(), Error> { | ----------------- expected `dependency::Error` because of this ... LL | Err(Error2)?; | -----------^ the trait `From<Error2>` is not implemented for `dependency::Error` | | | this can't be annotated with `?` because it has type `Result<_, Error2>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait help: the trait `From<Error2>` is not implemented for `dependency::Error` but trait `From<()>` is implemented for it --> replaced | LL | impl From<()> for Error { | ^^^^^^^^^^^^^^^^^^^^^^^ = help: for that trait implementation, expected `()`, found `Error2` = note: there are multiple different versions of crate `dependency` in the dependency graph = help: you can use `cargo tree` to explore your dependency tree ``` The existing checks rely on having access to the actual types/traits that diverged to detect they are called the same, come from different crates with the same name. The new check is less specific, merely looking to see if the crate name the involved type belongs has multiple crates. CC #78552.

rustbot assigned jieyouxu Dec 31, 2025

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 31, 2025

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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-review Status: Awaiting review from the assignee but also interested parties. labels Jan 3, 2026

This was referenced Jan 3, 2026

Rollup of 4 pull requests #150636

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Rollup of 5 pull requests #150638

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bors merged commit 78376fd into rust-lang:main Jan 3, 2026
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Detect cases where `?` is applied on a type that could be coming from a different crate version than expected #150558

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estebank commented Dec 31, 2025 •

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Detect cases where `?` is applied on a type that could be coming from a different crate version than expected #150558

Detect cases where `?` is applied on a type that could be coming from a different crate version than expected #150558

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