Strictly proof not tainted by errors in `TypeckResults`

Nobody has claimed this yet.

I get here from #125888.

For now there is a hack when calling tcx.typeck():
https://github.com/rust-lang/rust/blob/76c73827dcd0b363e60b22c3cef64bde4171bf17/compiler/rustc_hir_typeck/src/writeback.rs#L125-L130

so that in returned TypeckResults, the tainted_by_errors may be None even though there is actually some errors. And this could cause many ICEs, because some functions trust that there is no type errors, and whenever it encounters an error, it won't throw an error report and just panic (#125888 is an example).

In this tainted_by_errors function, I try to change the condition to if self.dcx().err_count_excluding_lint_errs() > 0, then return the ErrorGuaranteed, and find that it could resolve 62 ICEs.

Resolved ICE list


    [crashes] tests/crashes/110630.rs
    [crashes] tests/crashes/111709.rs
    [crashes] tests/crashes/111709-2.rs
    [crashes] tests/crashes/112623.rs
    [crashes] tests/crashes/113379.rs
    [crashes] tests/crashes/114663.rs
    [crashes] tests/crashes/115808.rs
    [crashes] tests/crashes/117795.rs
    [crashes] tests/crashes/118545.rs
    [crashes] tests/crashes/119701.rs
    [crashes] tests/crashes/119729.rs
    [crashes] tests/crashes/119786.rs
    [crashes] tests/crashes/120793-2.rs
    [crashes] tests/crashes/120793.rs
    [crashes] tests/crashes/120792.rs
    [crashes] tests/crashes/120873.rs
    [crashes] tests/crashes/121097.rs
    [crashes] tests/crashes/121127.rs
    [crashes] tests/crashes/121063.rs
    [crashes] tests/crashes/121052.rs
    [crashes] tests/crashes/121411.rs
    [crashes] tests/crashes/121429.rs
    [crashes] tests/crashes/121613-2.rs
    [crashes] tests/crashes/121613.rs
    [crashes] tests/crashes/121623.rs
    [crashes] tests/crashes/121816.rs
    [crashes] tests/crashes/121957-1.rs
    [crashes] tests/crashes/121957-2.rs
    [crashes] tests/crashes/122044.rs
    [crashes] tests/crashes/122587-1.rs
    [crashes] tests/crashes/121858.rs
    [crashes] tests/crashes/122259.rs
    [crashes] tests/crashes/122630.rs
    [crashes] tests/crashes/122681.rs
    [crashes] tests/crashes/122904-2.rs
    [crashes] tests/crashes/122904.rs
    [crashes] tests/crashes/122909.rs
    [crashes] tests/crashes/123255.rs
    [crashes] tests/crashes/123276.rs
    [crashes] tests/crashes/123690.rs
    [crashes] tests/crashes/124004.rs
    [crashes] tests/crashes/124021.rs
    [crashes] tests/crashes/124083.rs
    [crashes] tests/crashes/124164.rs
    [crashes] tests/crashes/124262.rs
    [crashes] tests/crashes/124182.rs
    [crashes] tests/crashes/124340.rs
    [crashes] tests/crashes/124563.rs
    [crashes] tests/crashes/124583.rs
    [crashes] tests/crashes/124436.rs
    [crashes] tests/crashes/124894.rs
    [crashes] tests/crashes/125155.rs
    [crashes] tests/crashes/125185.rs
    [crashes] tests/crashes/125553.rs
    [crashes] tests/crashes/125758.rs
    [crashes] tests/crashes/125801.rs
    [crashes] tests/crashes/125768.rs
    [crashes] tests/crashes/125769.rs
    [crashes] tests/crashes/125874.rs
    [crashes] tests/crashes/125888.rs
    [crashes] tests/crashes/125914.rs
    [crashes] tests/crashes/125992.rs

https://github.com/rust-lang/rust/blob/f6b4b71ef10307201b52c17b0f9dcf9557cd90ba/compiler/rustc_infer/src/infer/mod.rs#L1152-L1172

But it will also break many ui tests, because as the hack said, it will affect diagnostic spans pretty negatively. So I think a proper way to resolve that is return a new defined enum rather than Option, such as

https://github.com/rust-lang/rust/blob/f6b4b71ef10307201b52c17b0f9dcf9557cd90ba/compiler/rustc_middle/src/ty/typeck_results.rs#L161-L163

enum TaintedByErrors {
    Normal(ErrorGuaranteed),
    Opaque(ErrorGuaranteed),
    StrictlyNoError,
}

So that we can choose to either early return or do more diagnostics.

@rustbot label +I-ICE +T-compiler

Start with the writeback hack in compiler/rustc_hir_typeck/src/writeback.rs and inspect tainted_by_errors in compiler/rustc_infer/src/infer/mod.rs. Read the TypeckResults representation in compiler/rustc_middle/src/ty/typeck_results.rs, then review the listed ICE and UI tests. Done means distinguishing strict no-error results from results that should preserve diagnostic behavior without allowing ICEs.

Written by the indexing model from the issue text.

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