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carbon-lang/toolchain/parse/testdata/lambda/lambda.carbon
T
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
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/parse/testdata/lambda/lambda.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/parse/testdata/lambda/lambda.carbon
// --- basic.carbon
var a: auto = fn [T: type] (x: T) -> T { return x; };
var b: auto = fn (x: i32) => x;
var c: auto = fn { };
// --- fail_unconsumed_lambda_introducer.carbon
// Tests that the compiler does not crash when a LambdaIntroducer (`fn`)
// is left unconsumed inside an invalid binary operator sequence.
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+12]]:10: error: whitespace missing around binary operator [BinaryOperatorRequiresWhitespace]
// CHECK:STDERR: require j%-fn->>
// CHECK:STDERR: ^
// CHECK:STDERR:
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+8]]:16: error: expected expression [ExpectedExpr]
// CHECK:STDERR: require j%-fn->>
// CHECK:STDERR: ^
// CHECK:STDERR:
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+4]]:16: error: whitespace missing before binary operator [BinaryOperatorRequiresWhitespace]
// CHECK:STDERR: require j%-fn->>
// CHECK:STDERR: ^
// CHECK:STDERR:
require j%-fn->>
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+12]]:1: error: expected expression [ExpectedExpr]
// CHECK:STDERR:
// CHECK:STDERR: ^
// CHECK:STDERR:
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+8]]:1: error: expected `=>` or `{` after return type [ExpectedLambdaBodyAfterReturnType]
// CHECK:STDERR:
// CHECK:STDERR: ^
// CHECK:STDERR:
// CHECK:STDERR: fail_unconsumed_lambda_introducer.carbon:[[@LINE+4]]:1: error: expected `impls` in `require` declaration [RequireExpectedImpls]
// CHECK:STDERR:
// CHECK:STDERR: ^
// CHECK:STDERR:
// --- fail_expected_body.carbon
fn F() {
// CHECK:STDERR: fail_expected_body.carbon:[[@LINE+4]]:20: error: expected `->`, `=>`, or `{` [ExpectedLambdaBody]
// CHECK:STDERR: var x: auto = fn ;
// CHECK:STDERR: ^
// CHECK:STDERR:
var x: auto = fn ;
}
// --- fail_expected_body_after_return_type.carbon
fn G() {
// CHECK:STDERR: fail_expected_body_after_return_type.carbon:[[@LINE+4]]:27: error: expected `=>` or `{` after return type [ExpectedLambdaBodyAfterReturnType]
// CHECK:STDERR: var x: auto = fn -> i32 ;
// CHECK:STDERR: ^
// CHECK:STDERR:
var x: auto = fn -> i32 ;
}
// CHECK:STDOUT: - filename: basic.carbon
// CHECK:STDOUT: parse_tree: [
// CHECK:STDOUT: {kind: 'FileStart', text: ''},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'a'},
// CHECK:STDOUT: {kind: 'AutoTypeLiteral', text: 'auto'},
// CHECK:STDOUT: {kind: 'VarBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariablePattern', text: 'var', subtree_size: 4},
// 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: 'TypeTypeLiteral', text: 'type'},
// 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'},
// CHECK:STDOUT: {kind: 'LetBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ExplicitParamList', text: ')', subtree_size: 5},
// CHECK:STDOUT: {kind: 'IdentifierNameExpr', text: 'T'},
// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 2},
// CHECK:STDOUT: {kind: 'CodeBlockStart', text: '{'},
// CHECK:STDOUT: {kind: 'ReturnStatementStart', text: 'return'},
// 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: 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'},
// CHECK:STDOUT: {kind: 'VarBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariablePattern', text: 'var', subtree_size: 4},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'ExplicitParamListStart', text: '('},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'x'},
// CHECK:STDOUT: {kind: 'IntTypeLiteral', text: 'i32'},
// CHECK:STDOUT: {kind: 'LetBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ExplicitParamList', text: ')', subtree_size: 5},
// CHECK:STDOUT: {kind: 'TerseBodyArrow', text: '=>'},
// CHECK:STDOUT: {kind: 'IdentifierNameExpr', text: 'x'},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', subtree_size: 9},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 16},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'c'},
// CHECK:STDOUT: {kind: 'AutoTypeLiteral', text: 'auto'},
// CHECK:STDOUT: {kind: 'VarBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariablePattern', text: 'var', subtree_size: 4},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'CodeBlockStart', text: '{'},
// CHECK:STDOUT: {kind: 'CodeBlock', text: '}', subtree_size: 2},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', subtree_size: 4},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 11},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
// CHECK:STDOUT: - filename: fail_unconsumed_lambda_introducer.carbon
// CHECK:STDOUT: parse_tree: [
// CHECK:STDOUT: {kind: 'FileStart', text: ''},
// CHECK:STDOUT: {kind: 'RequireIntroducer', text: 'require'},
// CHECK:STDOUT: {kind: 'IdentifierNameExpr', text: 'j'},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: '>', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: '', has_error: yes},
// CHECK:STDOUT: {kind: 'InfixOperatorGreater', text: '>', has_error: yes, subtree_size: 3},
// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 4},
// CHECK:STDOUT: {kind: 'InvalidParse', text: '', has_error: yes},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', has_error: yes, subtree_size: 7},
// CHECK:STDOUT: {kind: 'PrefixOperatorMinus', text: '-', subtree_size: 8},
// CHECK:STDOUT: {kind: 'InfixOperatorPercent', text: '%', subtree_size: 10},
// CHECK:STDOUT: {kind: 'RequireDecl', text: '>', has_error: yes, subtree_size: 12},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
// CHECK:STDOUT: - filename: fail_expected_body.carbon
// CHECK:STDOUT: parse_tree: [
// CHECK:STDOUT: {kind: 'FileStart', text: ''},
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'IdentifierNameMaybeBeforeSignature', text: 'F'},
// CHECK:STDOUT: {kind: 'ExplicitParamListStart', text: '('},
// CHECK:STDOUT: {kind: 'ExplicitParamList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'x'},
// CHECK:STDOUT: {kind: 'AutoTypeLiteral', text: 'auto'},
// CHECK:STDOUT: {kind: 'VarBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariablePattern', text: 'var', subtree_size: 4},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', has_error: yes, subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 10},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 16},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
// CHECK:STDOUT: - filename: fail_expected_body_after_return_type.carbon
// CHECK:STDOUT: parse_tree: [
// CHECK:STDOUT: {kind: 'FileStart', text: ''},
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'IdentifierNameMaybeBeforeSignature', text: 'G'},
// CHECK:STDOUT: {kind: 'ExplicitParamListStart', text: '('},
// CHECK:STDOUT: {kind: 'ExplicitParamList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'IdentifierNameNotBeforeSignature', text: 'x'},
// CHECK:STDOUT: {kind: 'AutoTypeLiteral', text: 'auto'},
// CHECK:STDOUT: {kind: 'VarBindingPattern', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariablePattern', text: 'var', subtree_size: 4},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'LambdaIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'IntTypeLiteral', text: 'i32'},
// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 2},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'Lambda', text: 'fn', has_error: yes, subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableDecl', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
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