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Replace :! binding syntax with phase keywords and contextual defaults (#7479)

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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
This commit is contained in:
Chandler Carruth
2026-07-11 01:22:44 +00:00
committed by GitHub
parent bf106c3b4b
commit 8be274cf60
482 changed files with 16917 additions and 16226 deletions
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toolchain/check/testdata/function/definition/syntactic_merge.carbon
Vendored
+18 -18
View File
@@ -57,23 +57,23 @@ library "[[@TEST_NAME]]";
class C {}
// CHECK:STDERR: fail_only_implicit_params.carbon:[[@LINE+8]]:8: error: implicit parameters of functions must be constant [ImplictParamMustBeConstant]
// CHECK:STDERR: fn Foo[a: C];
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fn Foo[runtime a: C];
// CHECK:STDERR: ^~~~~~~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_only_implicit_params.carbon:[[@LINE+4]]:1: error: semantics TODO: `function with positional parameters` [SemanticsTodo]
// CHECK:STDERR: fn Foo[a: C];
// CHECK:STDERR: ^~~~~~~~~~~~~
// CHECK:STDERR: fn Foo[runtime a: C];
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
fn Foo[a: C];
fn Foo[runtime a: C];
// CHECK:STDERR: fail_only_implicit_params.carbon:[[@LINE+8]]:8: error: implicit parameters of functions must be constant [ImplictParamMustBeConstant]
// CHECK:STDERR: fn Foo[a: (C)] {}
// CHECK:STDERR: ^~~~~~
// CHECK:STDERR: fn Foo[runtime a: (C)] {}
// CHECK:STDERR: ^~~~~~~~~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_only_implicit_params.carbon:[[@LINE+4]]:1: error: semantics TODO: `function with positional parameters` [SemanticsTodo]
// CHECK:STDERR: fn Foo[a: (C)] {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~
// CHECK:STDERR: fn Foo[runtime a: (C)] {}
// CHECK:STDERR: ^~~~~~~~~~~~~~~~~~~~~~~~
// CHECK:STDERR:
fn Foo[a: (C)] {}
fn Foo[runtime a: (C)] {}
// --- fail_raw_identifier.carbon
@@ -149,15 +149,15 @@ library "[[@TEST_NAME]]";
class C {}
alias D = C;
fn Foo[a:! C]();
// CHECK:STDERR: fail_deduced_alias.carbon:[[@LINE+7]]:19: error: redeclaration syntax differs here [RedeclParamSyntaxDiffers]
// CHECK:STDERR: fn Foo[unused a:! D]() {}
// CHECK:STDERR: ^
// CHECK:STDERR: fail_deduced_alias.carbon:[[@LINE-4]]:12: note: comparing with previous declaration here [RedeclParamSyntaxPrevious]
// CHECK:STDERR: fn Foo[a:! C]();
// CHECK:STDERR: ^
fn Foo[a: C]();
// CHECK:STDERR: fail_deduced_alias.carbon:[[@LINE+7]]:18: error: redeclaration syntax differs here [RedeclParamSyntaxDiffers]
// CHECK:STDERR: fn Foo[unused a: D]() {}
// CHECK:STDERR: ^
// CHECK:STDERR: fail_deduced_alias.carbon:[[@LINE-4]]:11: note: comparing with previous declaration here [RedeclParamSyntaxPrevious]
// CHECK:STDERR: fn Foo[a: C]();
// CHECK:STDERR: ^
// CHECK:STDERR:
fn Foo[unused a:! D]() {}
fn Foo[unused a: D]() {}
// --- todo_fail_alias_in_return.carbon