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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
85 lines
2.6 KiB
Plaintext
85 lines
2.6 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/operators/as";
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import library "prelude/copy";
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import library "prelude/types/char_literal";
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import library "prelude/types/int_literal";
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import library "prelude/types/float_literal";
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interface UnsafeAs(Dest: type) {
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fn Convert(self) -> Dest;
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}
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interface As(Dest: type) {
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// TODO: extend UnsafeAs(Dest);
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fn Convert(self) -> Dest;
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}
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interface ImplicitAs(Dest: type) {
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// TODO: extend As(Dest);
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fn Convert(self) -> Dest;
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}
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// Workaround: ImplicitAs extends As.
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impl forall [U: type, T: ImplicitAs(U)] T as As(U) {
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fn Convert(self) -> U { return self.Convert(); }
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}
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// Workaround: As extends UnsafeAs.
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impl forall [U: type, T: As(U)] T as UnsafeAs(U) {
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fn Convert(self) -> U { return self.Convert(); }
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}
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// Copyable types have an identity conversion that performs a copy.
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impl forall [T: Copy] T as ImplicitAs(T) {
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fn Convert(self) -> Self { return self.(Copy.Op)(); }
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}
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// `const` can be added and removed when converting a value.
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impl forall [T: type, U: ImplicitAs(T)] U as ImplicitAs(const T) {
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fn Convert(self) -> const T { return self.Convert(); }
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}
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impl forall [T: type, U: ImplicitAs(T)] const U as ImplicitAs(T) {
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fn Convert(self) -> T { return (self as U).Convert(); }
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}
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// `const` can be added to a pointer.
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// TODO: This is also provided as a builtin conversion. We provide it here so
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// that Optional(T*) can implicitly convert to Optional(const T*). See #5750.
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impl forall [T: type] T* as ImplicitAs(const T*) {
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fn Convert(self) -> const T* = "pointer.unsafe_convert";
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}
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impl forall [T: type] T* as As(const T*) {
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fn Convert(self) -> const T* = "pointer.unsafe_convert";
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}
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// Pointer types can be unsafely cast to other pointer types.
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// TODO: Should `unsafe as` be able to remove `const`?
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impl forall [T: type, U: type] T* as UnsafeAs(U*) {
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fn Convert(self) -> U* = "pointer.unsafe_convert";
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}
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// Integer literals can be implicitly converted to floating-point literals.
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impl IntLiteral as ImplicitAs(FloatLiteral) {
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fn Convert(self) -> FloatLiteral = "int.convert_float_checked";
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}
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// Floating-point literals can be explicitly cast to integer literals.
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impl FloatLiteral as UnsafeAs(IntLiteral) {
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fn Convert(self) -> IntLiteral = "float.convert_int";
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}
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// Integer literals can be explicitly cast to char literals.
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impl IntLiteral as As(CharLiteral) {
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fn Convert(self) -> CharLiteral = "int.convert_char_literal";
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}
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interface IntFitsIn(Dest: type) {}
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interface FloatFitsIn(Src: type) {}
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