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carbon-lang/toolchain/check/testdata/choice/generic.carbon
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Chandler Carruth 8be274cf60 Replace :! binding syntax with phase keywords and contextual defaults (#7479) 
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
2026-07-11 01:22:44 +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/uint.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/choice/generic.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/choice/generic.carbon
//@dump-sem-ir-begin
choice Always(T: type) {
Sunny
}
//@dump-sem-ir-end
// CHECK:STDOUT: --- generic.carbon
// CHECK:STDOUT:
// CHECK:STDOUT: constants {
// CHECK:STDOUT: %type: type = facet_type <type> [concrete]
// CHECK:STDOUT: %.Self.frozen: %type = symbolic_binding .Self [symbolic_self]
// CHECK:STDOUT: %pattern_type: type = pattern_type type [concrete]
// CHECK:STDOUT: %T.patt: %pattern_type = symbolic_binding_pattern T, 0 [symbolic]
// CHECK:STDOUT: %T: type = symbolic_binding T, 0 [symbolic]
// CHECK:STDOUT: %Always.type: type = generic_class_type @Always [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %Always.generic: %Always.type = struct_value () [concrete]
// CHECK:STDOUT: %Always: type = class_type @Always, @Always(%T) [symbolic]
// CHECK:STDOUT: %struct_type.discriminant: type = struct_type {.discriminant: %empty_tuple.type} [concrete]
// CHECK:STDOUT: %complete_type: <witness> = complete_type_witness %struct_type.discriminant [concrete]
// CHECK:STDOUT: %empty_tuple: %empty_tuple.type = tuple_value () [concrete]
// CHECK:STDOUT: %struct: %struct_type.discriminant = struct_value (%empty_tuple) [concrete]
// CHECK:STDOUT: %require_complete: <witness> = require_complete_type %Always [symbolic]
// CHECK:STDOUT: %Always.val: %Always = struct_value (%empty_tuple) [symbolic]
// CHECK:STDOUT: %.4eb: ref %Always = temporary invalid, %Always.val [symbolic]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: %Always.decl: %Always.type = class_decl @Always [concrete = constants.%Always.generic] {
// CHECK:STDOUT: %T.patt.loc14_16.1: %pattern_type = symbolic_binding_pattern T, 0 [symbolic = %T.patt.loc14_16.2 (constants.%T.patt)]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %.loc14_18.1: type = splice_block %.loc14_18.2 [concrete = type] {
// CHECK:STDOUT: %.Self.frozen: %type = symbolic_binding .Self [symbolic_self = constants.%.Self.frozen]
// CHECK:STDOUT: %.loc14_18.2: type = type_literal type [concrete = type]
// CHECK:STDOUT: }
// CHECK:STDOUT: %T.loc14_16.2: type = symbolic_binding T, 0 [symbolic = %T.loc14_16.1 (constants.%T)]
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: generic class @Always(%T.loc14_16.2: type) {
// CHECK:STDOUT: %T.patt.loc14_16.2: %pattern_type = symbolic_binding_pattern T, 0 [symbolic = %T.patt.loc14_16.2 (constants.%T.patt)]
// CHECK:STDOUT: %T.loc14_16.1: type = symbolic_binding T, 0 [symbolic = %T.loc14_16.1 (constants.%T)]
// CHECK:STDOUT:
// CHECK:STDOUT: !definition:
// CHECK:STDOUT: %Always: type = class_type @Always, @Always(%T.loc14_16.1) [symbolic = %Always (constants.%Always)]
// CHECK:STDOUT: %require_complete: <witness> = require_complete_type %Always [symbolic = %require_complete (constants.%require_complete)]
// CHECK:STDOUT: %Always.val: @Always.%Always (%Always) = struct_value (constants.%empty_tuple) [symbolic = %Always.val (constants.%Always.val)]
// CHECK:STDOUT: %.loc16_1.13: ref @Always.%Always (%Always) = temporary invalid, %Always.val [symbolic = %.loc16_1.13 (constants.%.4eb)]
// CHECK:STDOUT:
// CHECK:STDOUT: class {
// CHECK:STDOUT: %complete_type: <witness> = complete_type_witness constants.%struct_type.discriminant [concrete = constants.%complete_type]
// CHECK:STDOUT: %.loc16_1.1: %empty_tuple.type = tuple_literal () [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %empty_tuple: %empty_tuple.type = tuple_value () [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc16_1.2: %empty_tuple.type = converted %.loc16_1.1, %empty_tuple [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc16_1.3: %struct_type.discriminant = struct_literal (%.loc16_1.2) [concrete = constants.%struct]
// CHECK:STDOUT: %.loc16_1.4: ref @Always.%Always (%Always) = temporary_storage
// CHECK:STDOUT: %.loc16_1.5: ref %empty_tuple.type = class_element_access %.loc16_1.4, element0
// CHECK:STDOUT: %.loc16_1.6: init %empty_tuple.type to %.loc16_1.5 = tuple_init () [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc16_1.7: init %empty_tuple.type = converted %.loc16_1.2, %.loc16_1.6 [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc16_1.8: init %empty_tuple.type to %.loc16_1.5 = in_place_init %.loc16_1.7 [concrete = constants.%empty_tuple]
// CHECK:STDOUT: %.loc16_1.9: init @Always.%Always (%Always) to %.loc16_1.4 = class_init (%.loc16_1.8) [symbolic = %Always.val (constants.%Always.val)]
// CHECK:STDOUT: %.loc16_1.10: init @Always.%Always (%Always) = converted %.loc16_1.3, %.loc16_1.9 [symbolic = %Always.val (constants.%Always.val)]
// CHECK:STDOUT: %.loc16_1.11: ref @Always.%Always (%Always) = temporary %.loc16_1.4, %.loc16_1.10 [symbolic = %.loc16_1.13 (constants.%.4eb)]
// CHECK:STDOUT: %.loc16_1.12: @Always.%Always (%Always) = acquire_value %.loc16_1.11 [symbolic = %Always.val (constants.%Always.val)]
// CHECK:STDOUT: %Sunny: @Always.%Always (%Always) = wrapper_binding Sunny, %.loc16_1.12
// CHECK:STDOUT: complete_type_witness = %complete_type
// CHECK:STDOUT:
// CHECK:STDOUT: !members:
// CHECK:STDOUT: .Self = constants.%Always
// CHECK:STDOUT: .Sunny = %Sunny
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: specific @Always(constants.%T) {
// CHECK:STDOUT: %T.patt.loc14_16.2 => constants.%T.patt
// CHECK:STDOUT: %T.loc14_16.1 => constants.%T
// CHECK:STDOUT: }
// CHECK:STDOUT:
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