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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
55 lines
2.1 KiB
Plaintext
55 lines
2.1 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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package Core library "prelude/default";
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import library "prelude/types/bool";
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import library "prelude/types/int_literal";
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// Provides the default value of an object. If implemented for a type `T`, this
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// is used to initialize declarations without an explicit initializer, such as
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// `var x: T;`, and leaves them in a fully-formed state.
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interface Default { fn Op() -> Self; }
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// Indicates that a type permits unformed initialization, which leaves the
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// object in a state where calling the destructor is valid but optional, and no
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// other operations on the object except for reinitialization are permitted.
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interface UnformedInit {
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// TODO: This should probably be:
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// let StructT: type;
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// fn Op() -> StructT;
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// and should be able to initialize a subset of the fields. For now we always
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// leave the object uninitialized when it is in an unformed state.
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// See https://github.com/carbon-language/carbon-lang/pull/5913
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}
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// Implementations for some builtin types. These need to be here to satisfy the
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// orphan rule because these builtin types have no associated library of their
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// own.
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impl bool as UnformedInit {}
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impl forall [T: type] T* as UnformedInit {}
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impl forall [T: UnformedInit, N: IntLiteral] array(T, N) as UnformedInit {}
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// TODO: Generalize these to apply to tuples and structs containing only
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// `UnformedInit` types.
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impl () as UnformedInit {}
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impl {} as UnformedInit {}
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// Provides a default, possibly unformed, value of an object. This should not be
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// implemented directly. Instead, implement `Default` to provide a fully-formed
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// state or (eventually) `UnformedInit` to provide an unformed state.
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interface DefaultOrUnformed {
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// TODO: This should return `MaybeUnformed(Self)` once that is supported.
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fn Op() -> Self;
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}
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final impl forall [T: Default] T as DefaultOrUnformed {
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fn Op() -> Self {
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return T.(Default.Op)();
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}
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}
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impl forall [T: UnformedInit] T as DefaultOrUnformed {
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fn Op() -> Self = "make_uninitialized";
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}
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