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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/parse/testdata/lambda/lambda.carbon
Vendored
+6 -7
View File
@@ -10,7 +10,7 @@
// --- basic.carbon
var a: auto = fn [T:! type] (x: T) -> T { return x; };
var a: auto = fn [T: type] (x: T) -> T { return x; };
var b: auto = fn (x: i32) => x;
var c: auto = fn { };
@@ -76,11 +76,10 @@ fn G() {
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'ImplicitParamListStart', text: '['},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'T'},
// CHECK:STDOUT: {kind: 'CompileTimeBindingPatternStart', text: ':!', subtree_size: 2},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'T'},
// CHECK:STDOUT: {kind: 'TypeTypeLiteral', text: 'type'},
// CHECK:STDOUT: {kind: 'CompileTimeBindingPattern', text: ':!', subtree_size: 4},
// CHECK:STDOUT: {kind: 'ImplicitParamList', text: ']', subtree_size: 6},
// CHECK:STDOUT: {kind: 'LetBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ImplicitParamList', text: ']', subtree_size: 5},
// CHECK:STDOUT: {kind: 'ExplicitParamListStart', text: '('},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'x'},
// CHECK:STDOUT: {kind: 'IdentifierNameExpr', text: 'T'},
@@ -93,8 +92,8 @@ fn G() {
// CHECK:STDOUT: {kind: 'IdentifierNameExpr', text: 'x'},
// CHECK:STDOUT: {kind: 'ReturnStatement', text: ';', subtree_size: 3},
// CHECK:STDOUT: {kind: 'CodeBlock', text: '}', subtree_size: 5},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', subtree_size: 20},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 27},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', subtree_size: 19},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 26},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'b'},
// CHECK:STDOUT: {kind: 'AutoTypeLiteral', text: 'auto'},