Fix ICE caused by const block pattern

[Rohithkumar2030]

Summary

This PR fixes an internal compiler error (ICE) occurring when matching a deref pattern inside a const block.

Changes made

• Adjusted logic in rustc_hir_typeck from span_bug to self.tcx.dcx().span_delayed_bug
• Added a test: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs
• Generated the corresponding .stderr file for the test using --bless

Notes

• Verified locally with ./x.py test
• Open for review and feedback

Fixes #148138

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  • e1f00a3

[Rohithkumar2030]

r? @Nadrieril

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They may take a while to respond.

[rust-log-analyzer]

The job aarch64-gnu-llvm-20-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

failures:

---- [ui] tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs stdout ----

error: 4 diagnostics reported in JSON output but not expected in test file
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:14:9: ERROR: expected a pattern, found a function call [E0532]
  expected on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:4:1
  expected on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:6:1
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:14:9: ERROR: usage of qualified paths in this context is experimental [E0658]
  expected on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:7:1
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:11:12: WARN: the feature `deref_patterns` is incomplete and may not be safe to use and/or cause compiler crashes [incomplete_features]
  expected on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:8:1
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:14:9: ERROR: expected tuple struct or tuple variant, found associated function `<[_]>::into_vec` [E0164]
  expected on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:9:1

error: 5 diagnostics expected in test file but not reported in JSON output
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:4:1: ERROR: expected a pattern
  reported on different line: tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:14:9
tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs:6:1: ERROR: expected a pattern, found a function call
---

thread '[ui] tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs' panicked at src/tools/compiletest/src/runtest.rs:923:13:
errors differ from expected
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/pattern/deref-patterns/ice-adjust-mode-unimplemented-for-constblock" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"

stack backtrace:
   5: __rustc::rust_begin_unwind
             at /rustc/3b4dd9bf1410f8da6329baa36ce5e37673cbbd1f/library/std/src/panicking.rs:698:5
   6: core::panicking::panic_fmt

[dianne]

I'm sorry to be the bearer of inconvenient news, but I think the span_bug! is correct; the ICE is it working as intended to catch a bug elsewhere in the compiler. From what I can tell, the real problem is at least partially¹ that the ICEing test bypassed the validation in the parser that const blocks don't appear in patterns². If it's at all reasonable, I think the ConstBlock variant of hir::PatExprKind should be removed entirely and this should be caught during AST lowering in rustc_ast_lowering::LoweringContext::lower_expr_within_pat.

It's a little worrisome that the ICEing example confused the parser like that.. I haven't looked into it, but hopefully it only happens for code that would error anyway.

Footnotes

1. I haven't looked into this deeply enough to make sure there isn't anything else bad happening with the expansion of vec! in pattern position ^^ ↩

2. If the validation worked, it'd be a hir::PatExprKind::Lit of LitKind::Err in the HIR so the debug assertion wouldn't get tripped. ↩

[Kivooeo]

That's interesting because @Nadrieril said that this is correct to replace with span_delayed_bug: #148138 (comment)

[Nadrieril]

That's on me for being too quick to jump to conclusions, my bad. I trust @dianne 's analysis

[oli-obk]

• Verified locally with ./x.py test

Considering the tests are failing I don't see you actually did that.

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