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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
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/testdata/class/method/fail_generic_method.carbon
Vendored
+12 -12
View File
@@ -12,7 +12,7 @@
class I {}
class Class(T:! type) {
class Class(T: type) {
var a: T;
fn F(self, n: T);
}
@@ -20,18 +20,18 @@ class Class(T:! type) {
// TODO: The follow-on errors here aren't great. Investigate whether we can
// enter the scope anyway if the parameters don't match.
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE+15]]:17: error: type `<pattern for I>` of parameter 1 in redeclaration differs from previous parameter type `<pattern for type>` [RedeclParamDiffersType]
// CHECK:STDERR: fn Class(unused N:! I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^~~~~
// CHECK:STDERR: fn Class(unused N: I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE-10]]:13: note: previous declaration's corresponding parameter here [RedeclParamPrevious]
// CHECK:STDERR: class Class(T:! type) {
// CHECK:STDERR: ^~~~~~~~
// CHECK:STDERR: class Class(T: type) {
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE+8]]:33: error: name `Self` not found [NameNotFound]
// CHECK:STDERR: fn Class(unused N:! I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^~~~
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE+8]]:32: error: name `Self` not found [NameNotFound]
// CHECK:STDERR: fn Class(unused N: I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE+4]]:49: error: name `T` not found [NameNotFound]
// CHECK:STDERR: fn Class(unused N:! I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^
// CHECK:STDERR: fail_generic_method.carbon:[[@LINE+4]]:48: error: name `T` not found [NameNotFound]
// CHECK:STDERR: fn Class(unused N: I).F(unused self, unused n: T) {}
// CHECK:STDERR: ^
// CHECK:STDERR:
fn Class(unused N:! I).F(unused self, unused n: T) {}
fn Class(unused N: I).F(unused self, unused n: T) {}