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carbon-lang/toolchain/check/testdata/impl/basic.carbon
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Dana Jansens a5ba0a0f45 Use GetConstantValueInSpecific to get the impl's specific interface after deduction (#7584) 
During impl lookup, for each (generic) impl candidate, we form a
specific for that impl by deducing its generic arguments. Then we
compare the query interface against the impl's specific interface. That
comparison needs the deduced arguments applied to the impl's specific
interface. Previously we were doing this by getting the impl's
constraint facet type with the impl's specific applied (via
`GetConstantValueInSpecific()`) and then identifying that facet type
with the impl's deduced self.

Identify is a fairly expensive operation. It runs subst, trying to
replace `.Self` references. It walks named constraints. It collects
require declarations. We're looking at making it do _more_ in the future
too, including rewrite constraint resolution and collecting rewrite and
same-type constraints. For this reason we have a cache to make it cheap
on the second run, but it's still a very heavyweight operation to
involve in impl lookup, when all we want is to apply the impl's specific
to its target interface.

We almost have all the information we need to avoid the identification
step. We have the impl's specific after deduction. And we have the
SpecificInterface that the impl is targeting in the `Impl` struct. When
we form the specific for the impl itself, we resolve the declaration
block and form new constant values for all instructions in there, but
that does not cover the SpecificInterface that we're storing in the
`Impl` struct. So we add a new instruction to the impl's eval block,
which will be symbolic when the impl is generic and the target interface
depends on a generic parameter. And we store the `InstId` in the `Impl`
struct. This allows us to gets its constant value later with the impl's
specific applied. From that constant value we can then pull out the
SpecificInterface that the impl is targeting.
2026-07-30 19:59:10 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/none.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/impl/basic.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/impl/basic.carbon
// --- basic.carbon
library "[[@TEST_NAME]]";
interface Simple {
fn F();
}
class C {}
//@dump-sem-ir-begin
impl C as Simple {
fn F() {}
}
//@dump-sem-ir-end
// --- fail_invalid_impl.carbon
library "[[@TEST_NAME]]";
interface I {
fn Op(self);
}
class C {}
// This produces an invalid impl.
// CHECK:STDERR: fail_invalid_impl.carbon:[[@LINE+4]]:6: error: name `Unknown` not found [NameNotFound]
// CHECK:STDERR: impl Unknown as I {
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
impl Unknown as I {
fn Op(unused self) {}
}
// --- fail_import_invalid_impl.carbon
library "[[@TEST_NAME]]";
import library "invalid_impl";
fn F() {
// This impl doesn't exist, but it still tests that we can ignore the
// `impl Unknown as I` on import.
// CHECK:STDERR: fail_import_invalid_impl.carbon:[[@LINE+4]]:3: error: cannot access member of interface `I` in type `type` that does not implement that interface [MissingImplInMemberAccess]
// CHECK:STDERR: C.(I.Op)();
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR:
C.(I.Op)();
}
// --- fail_conflicting_bad_impls.carbon
library "[[@TEST_NAME]]";
interface I {}
class C(T: type) {}
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+4]]:12: error: name `invalid` not found [NameNotFound]
// CHECK:STDERR: final impl invalid as I {}
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
final impl invalid as I {}
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+11]]:12: error: name `invalid` not found [NameNotFound]
// CHECK:STDERR: final impl invalid as I {}
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+7]]:1: error: redefinition of `impl <error> as I` [ImplRedefinition]
// CHECK:STDERR: final impl invalid as I {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE-8]]:1: note: previous definition was here [ImplPreviousDefinition]
// CHECK:STDERR: final impl invalid as I {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
final impl invalid as I {}
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+4]]:12: error: name `alsoinvalid` not found [NameNotFound]
// CHECK:STDERR: final impl alsoinvalid as I {}
// CHECK:STDERR: ^~~~~~~~~~~
// CHECK:STDERR:
final impl alsoinvalid as I {}
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+4]]:14: error: name `invalid` not found [NameNotFound]
// CHECK:STDERR: final impl C(invalid) as I {}
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
final impl C(invalid) as I {}
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+11]]:14: error: name `invalid` not found [NameNotFound]
// CHECK:STDERR: final impl C(invalid) as I {}
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE+7]]:1: error: redefinition of `impl <error> as I` [ImplRedefinition]
// CHECK:STDERR: final impl C(invalid) as I {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR: fail_conflicting_bad_impls.carbon:[[@LINE-8]]:1: note: previous definition was here [ImplPreviousDefinition]
// CHECK:STDERR: final impl C(invalid) as I {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
final impl C(invalid) as I {}
// CHECK:STDOUT: --- basic.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %Simple.type: type = facet_type <@Simple> [concrete]
// CHECK:STDOUT: %C: type = class_type @C [concrete]
// CHECK:STDOUT: %.dd3: <witness> = impl_self_witness %C, @Simple [concrete]
// CHECK:STDOUT: %Simple.impl_witness: <witness> = impl_witness @C.as.Simple.impl.%Simple.impl_witness_table [concrete]
// CHECK:STDOUT: %C.as.Simple.impl.F.type: type = fn_type @C.as.Simple.impl.F [concrete]
// CHECK:STDOUT: %C.as.Simple.impl.F: %C.as.Simple.impl.F.type = struct_value () [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: impl_decl @C.as.Simple.impl [concrete] {} {
// CHECK:STDOUT: %C.ref: type = name_ref C, file.%C.decl [concrete = constants.%C]
// CHECK:STDOUT: %Simple.ref: type = name_ref Simple, file.%Simple.decl [concrete = constants.%Simple.type]
// CHECK:STDOUT: }
// CHECK:STDOUT: %.loc11: <witness> = impl_self_witness @C.as.Simple.impl.%C.ref, @Simple [concrete = constants.%.dd3]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: impl @C.as.Simple.impl: %C.ref as %Simple.ref {
// CHECK:STDOUT: %C.as.Simple.impl.F.decl: %C.as.Simple.impl.F.type = fn_decl @C.as.Simple.impl.F [concrete = constants.%C.as.Simple.impl.F] {} {}
// CHECK:STDOUT: %Simple.impl_witness_table = impl_witness_table (%C.as.Simple.impl.F.decl), @C.as.Simple.impl [concrete]
// CHECK:STDOUT: %Simple.impl_witness: <witness> = impl_witness %Simple.impl_witness_table [concrete = constants.%Simple.impl_witness]
// CHECK:STDOUT:
// CHECK:STDOUT: !members:
// CHECK:STDOUT: .F = %C.as.Simple.impl.F.decl
// CHECK:STDOUT: extend %Simple.ref
// CHECK:STDOUT: witness = %Simple.impl_witness
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @C.as.Simple.impl.F() {
// CHECK:STDOUT: !entry:
// CHECK:STDOUT: return
// CHECK:STDOUT: }
// CHECK:STDOUT:
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