Handle non-type args in TraitRefPrintSugared#153902
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Handle non-type args in TraitRefPrintSugared#153902ViewWay wants to merge 2 commits intorust-lang:mainfrom
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March 14, 2026 21:37
… trait object types This is a cherry-pick of PR #153738 Problem: - PR #150843 introduced a regression where eager type aliases containing dyn Trait (with associated consts) would incorrectly report 'trait is not dyn compatible' errors - This affected 254 crates depending on old bitvec versions Root cause: - When checking for unspecified assoc items in trait object types, we were filtering for all associated consts (is_const()) - But eager type aliases don't get wfchecked at definition site - This broke the assumption that dyn-incompatible traits would be rejected early Fix: - Changed is_const() to is_type_const() to only check type-level associated consts, not regular associated consts - Regular associated consts cannot be bound in trait object types anyway, so checking them was unnecessary Modified files: - compiler/rustc_hir_analysis/src/hir_ty_lowering/dyn_trait.rs - compiler/rustc_middle/src/ty/assoc.rs - compiler/rustc_middle/src/ty/sty.rs - compiler/rustc_sanitizers/src/cfi/typeid/itanium_cxx_abi/transform.rs - tests/ui/type-alias/lack-of-wf.rs (new test) Fixes: #153731
The issue was that `TraitRefPrintSugared` called `type_at(1)` which panics when the argument is not a type (e.g., an inference variable). This can happen when there are prior errors in user code, such as incorrect trait parameters with paren sugar syntax. The fix uses `get(1).and_then(|arg| arg.as_type())` to safely check if the argument is a type before accessing it, falling back to the default printing path if not.
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fmease
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For the love of god, please drop your cherry-pick of the commit I authored in open PR RUST-153738. It makes no sense whatsoever to take ownership of it & to include it here and in your ~5 other PRs. Your PRs can't proceed otherwise.
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Fixes #153853.
The
TraitRefPrintSugaredcalledtype_at(1)which panics when the argument is not a type (e.g., an inference variable).This can happen when there are prior errors in user code, such as incorrect trait parameters with paren sugar syntax.
The fix uses
get(1).and_then(|arg| arg.as_type())to safely check if the argument is a type before accessing it, falling back to the default printing path if not.