regression: cannot find type `SourceFile` in crate `proc_macro`

[BoxyUwU]

• https://crater-reports.s3.amazonaws.com/beta-rustdoc-1.88-1/beta-2025-05-26/reg/safe-proc-macro2-1.0.94/log.txt
• and many others, there are just thousands and thousands of occurances of this in the beta rustdoc crater run :thonk:

[INFO] [stdout] error[E0412]: cannot find type `SourceFile` in crate `proc_macro`
[INFO] [stdout]    --> src/wrapper.rs:366:26
[INFO] [stdout]     |
[INFO] [stdout] 366 |     Compiler(proc_macro::SourceFile),
[INFO] [stdout]     |                          ^^^^^^^^^^ not found in `proc_macro`
[INFO] [stdout]     |
[INFO] [stdout] help: consider importing one of these structs
[INFO] [stdout]     |
[INFO] [stdout] 1   + use crate::SourceFile;
[INFO] [stdout]     |
[INFO] [stdout] 1   + use crate::fallback::SourceFile;
[INFO] [stdout]     |
[INFO] [stdout] help: if you import `SourceFile`, refer to it directly
[INFO] [stdout]     |
[INFO] [stdout] 366 -     Compiler(proc_macro::SourceFile),
[INFO] [stdout] 366 +     Compiler(SourceFile),
[INFO] [stdout]     |

[bjorn3]

This is probably just proc-macro2 detecting that the rustc supports unstable features at all and then assumes that all unstable features it thinks exist haven't changed since it was released (or maybe in this case do already exist in the rustc version it gets compiled with).

[Nemo157]

proc-macro2 actually compiles a probe file to decide whether to enable nightly features. So it seems there's something a little weird going on to make that pass on beta.

[Nemo157]

"-e" "RUSTC_BOOTSTRAP=1"

It seems that nightly features are enabled in that run, so this is just the lack of dtolnay/proc-macro2#497 from 1.0.95 updating the nightly APIs that proc-macro2 uses.

[bjorn3]

That probe file didn't reference SourceFile even before dtolnay/proc-macro2#497.

[Nemo157]

Yes, the probe file was incorrect in what API it used which is why 1.0.94 is broken on nightly/RUSTC_BOOTSTRAP, but it at least should always fail to compile on any stable compiler since it uses #![feature].