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Avoid symbolic witnesses for .Self in an impl decl (#7564)

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Point symbolic witnesses into `.Self` written inside an impl decl at the
impl that is being declared. This is tricky because the impl does not
yet exist. So we use a new instruction `ImplSelfWitness` which _will_ be
replaced by the `ImplWitness` once it becomes available. The
`ImplSelfWitness` acts like a symbolic witness, except it does not
perform lookup, since we know which impl we will get a witness from.

This prevents us from finding other impls when performing lookups into
`.Self` in an impl decl, which produces incorrect/incoherent results.
This commit is contained in:
Dana Jansens
2026-07-29 16:25:23 +00:00
committed by GitHub
parent 2ac425e591
commit f51c075f8b
94 changed files with 3221 additions and 2797 deletions
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toolchain/check/testdata/struct/import.carbon
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+2 -2
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@@ -291,12 +291,12 @@ fn F() -> {.x: i32} {
// CHECK:STDOUT: %struct_type.x: type = struct_type {.x: %i32} [concrete]
// CHECK:STDOUT: %C: type = class_type @C [concrete]
// CHECK:STDOUT: %I.type: type = facet_type <@I> [concrete]
// CHECK:STDOUT: %int_1: %i32 = int_value 1 [concrete]
// CHECK:STDOUT: %struct: %struct_type.x = struct_value (%int_1) [concrete]
// CHECK:STDOUT: %I.impl_witness: <witness> = impl_witness imports.%I.impl_witness_table [concrete]
// CHECK:STDOUT: %I.facet: %I.type = facet_value %C, (%I.impl_witness) [concrete]
// CHECK:STDOUT: %I.assoc_type: type = assoc_entity_type @I [concrete]
// CHECK:STDOUT: %assoc0.d9a: %I.assoc_type = assoc_entity element0, imports.%Main.import_ref.a1f [concrete]
// CHECK:STDOUT: %int_1: %i32 = int_value 1 [concrete]
// CHECK:STDOUT: %struct: %struct_type.x = struct_value (%int_1) [concrete]
// CHECK:STDOUT: %Copy.type: type = facet_type <@Copy> [concrete]
// CHECK:STDOUT: %Int.as.Copy.impl.Op.type.ac8: type = fn_type @Int.as.Copy.impl.Op, @Int.as.Copy.impl(%N) [symbolic]
// CHECK:STDOUT: %Int.as.Copy.impl.Op.5e0: %Int.as.Copy.impl.Op.type.ac8 = struct_value () [symbolic]