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Chandler Carruth
8be274cf60
Implement the toolchain side of proposal #7254, removing the `:!` binding syntax for generic and template parameters in favor of the keywords `generic`, `template`, and `runtime` plus contextual defaults for phase. For valid programs this is semantics-preserving: each binding resolves to the same phase, and produces the same SemIR, as it did under `:!`/`:`. The parser derives a binding's phase from its syntactic context plus any explicit phase keyword; new diagnostics and error recovery for misused keywords are described below. Implementation details for each component: - Lexer: remove the `:!` (`ColonExclaim`) token, move its virtual parse-node budget onto `:`, and add the `generic` and `runtime` keywords. - Parser: thread a `BindingContext` (`ExplicitParam`, `DeducedParam`, or `CompileTimeEntityParam`) from declaration introducers down through parameter lists to each binding pattern, using a one-token lookahead to distinguish a name-qualifier parameter list from a declaration's own final list. Parameters of a compile-time entity (`class`, `interface`, `constraint`, `choice`, `alias`, `export`, `namespace`) and deduced `[]` parameters default to checked generic; explicit function parameters and local bindings default to runtime. `HandleBindingPattern` resolves the phase from that context plus the keyword: a `generic` keyword needs no node of its own (the phase is carried by the binding's node kind), while a `runtime` keyword is preserved as a `RuntimeBindingName` node so `check` can name it in a diagnostic. A phase keyword that is merely redundant with the contextual default is diagnosed here, without invalidating the parse tree. - Check: a phase keyword that is invalid for its context (for example `runtime` on a checked-generic parameter) is diagnosed here, and recovers by building an error binding that still introduces the name so that later uses of it do not produce cascading errors. The removed `:!` syntax is now rejected as an ordinary parse error. The `form`/`:?`/`->?` ("extended types") portion of proposal #7254 is left for a separate change. Assisted-by: Claude Code
62 lines
2.4 KiB
Plaintext
62 lines
2.4 KiB
Plaintext
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/none.carbon
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//
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// AUTOUPDATE
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// TIP: To test this file alone, run:
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// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/impl/lookup/access.carbon
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// TIP: To dump output, run:
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// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/impl/lookup/access.carbon
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// --- fail_todo_impl_witness_access_in_impl_type_structure.carbon
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library "[[@TEST_NAME]]";
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interface X(T: type) {}
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interface Y {
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let Y1: type;
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}
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interface Z {
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let Z1: type;
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}
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// There's 2 ImplWitnessAccess instructions in the type, but they together
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// resolve to a symbolic type value, so the type structure is: `? as X(?)`
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impl forall [T: Z where .Z1 impls Y] T as X(T.Z1.(Y.Y1)) {}
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class C(W: type) {
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impl as Y where .Y1 = W {}
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}
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fn F(generic V: Z where .Z1 = C({})) {
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// The type stucture is `? as X({})` which will match the impl's less specific
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// `? as X(?)`, then the impl will deduce the parameter of `X` to be `{}` from
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// the type of `V`. This would fail if ImplWitnessAccess instructions were
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// treated as Concrete in the type structure, since the impl would have a
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// different concrete value (an ImplWitnessAccess) than the query (a
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// StructValue).
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V as X({});
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}
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fn G(generic V: Z where .Z1 impls Y) {
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// The type structure is `? as X(?)`, also built from ImplWitnessAccess insts,
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// which will match the impl's `? as X(?)`.
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V as X(V.(Z.Z1).(Y.Y1));
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}
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fn H(generic U: type, generic V: Z where .Z1 = C(U)) {
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// The type structure is `? as X(?)`, without using an ImplWitnessAccess,
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// which will match the impl's `? as X(?)`. This would fail if
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// ImplWitnessAccess instructions were treated as Concrete in the type
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// structure, since the impl's type structure would be more specific than the
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// query's.
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//
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// TODO: This should pass.
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// CHECK:STDERR: fail_todo_impl_witness_access_in_impl_type_structure.carbon:[[@LINE+4]]:3: error: cannot convert type `V` that implements `Z where .(Z.Z1) = C(U)` into type implementing `X(U)` [ConversionFailureFacetToFacet]
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// CHECK:STDERR: V as X(U);
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// CHECK:STDERR: ^~~~~~~~~
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// CHECK:STDERR:
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V as X(U);
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}
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