Codegen single-non-ZST-field constants with name-keyed struct fields - #4724
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feliperodri merged 2 commits intoAug 14, 2026
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try_codegen_constant built the field-value list in declaration order and used the positional struct constructor, but the goto struct type lists fields in LAYOUT order. For constants whose layout reorders fields (e.g. a (Wrap(u8), u16) pair placing the u16 first), this ICEd with 'value type does not match field type' (surfaced by yansi and bitvec in a crates.io autoharness sweep). Key the values by the variant's field names instead. Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>
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Pull request overview
Fixes an ICE in try_codegen_constant when codegenning struct constants whose field layout order differs from declaration order by switching from positional struct initialization to name-keyed field initialization, aligning with the goto struct’s layout-based field ordering.
Changes:
- Build struct constant initializers as a name-keyed map of field values and use
Expr::struct_exprinstead ofstruct_expr_from_values. - Add a regression test intended to cover layout-vs-declaration field order mismatches in constant struct codegen.
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Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| kani-compiler/src/codegen_cprover_gotoc/codegen/operand.rs | Switch constant struct expansion to name-keyed field initialization to match goto struct layout order. |
| tests/kani/Structs/const_struct_layout_order.rs | Add regression test for struct-constant codegen with layout-reordered fields. |
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The `try_codegen_constant` fix only applies to constant structs with a single non-ZST field (`non_zst_types.len() == 1`). The original test used a `Pair` with two non-ZST fields (`Wrap(u8)` and `u16`), which takes the separate allocation branch and never reaches the name-keyed `struct_expr` path, so it did not cover the regression. Replace it with a struct that has exactly one non-ZST field: a zero-sized `Marker` declared before a higher-aligned `u64`, so layout order (`u64` first) differs from declaration order. Verified that this reproduces the "value type does not match field type" ICE on the pre-fix compiler and passes with the fix. Signed-off-by: Felipe Monteiro <felisous@amazon.com>
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try_codegen_constantbuilt the field-value list in declaration order and used the positional struct constructor, but the goto struct type lists fields in layout order. For constants whose layout reorders fields (e.g. a(Wrap(u8), u16)pair placing theu16first), this ICEd with value type does not match field type.Surfaced by yansi and bitvec in a top-500 crates.io autoharness sweep (tracking #3832); the fix and regression test are independent of autoharness.
Changes
struct_expr) instead of position (struct_expr_from_values).By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.