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Parsing support for if expressions. (#2883)

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We model `if a then b else` as a prefix operator for parsing precedence purposes. The rule that a statement starting with `if` is never an `if` expression is handled implicitly because the statement parser never invokes the expression parser for a statement starting with `if`.

This exposed a bug in our diagnosis of the whitespace rule for prefix operators, which was incorrectly being applied to non-symbolic operators in some cases, and was producing a bogus second diagnostic in some cases, which is also fixed here.
This commit is contained in:
Richard Smith
2023-06-09 16:41:10 -07:00
committed by GitHub
parent 4e1adcf4c7
commit 2c45cb3be8
18 changed files with 400 additions and 22 deletions
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toolchain/parser/testdata/if_expression/basic.carbon
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'b'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'bool'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ParameterListComma', text: ','},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'x'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ParameterListComma', text: ','},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'y'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 13},
// CHECK:STDOUT: {kind: 'NameReference', text: 'bool'},
// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 18},
// CHECK:STDOUT: {kind: 'ReturnStatementStart', text: 'return'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'IfExpressionThen', text: 'then'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'x'},
// CHECK:STDOUT: {kind: 'IfExpressionElse', text: 'else'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'y'},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', subtree_size: 6},
// CHECK:STDOUT: {kind: 'ReturnStatement', text: ';', subtree_size: 8},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 27},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F(b: bool, x: i32, y: i32) -> bool {
return if b then x else y;
}
toolchain/parser/testdata/if_expression/fail_condition_missing.carbon
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'n'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', has_error: yes, subtree_size: 6},
// CHECK:STDOUT: {kind: 'VariableDeclaration', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_condition_missing.carbon:[[@LINE+1]]:18: Expected expression.
var n: i32 = if;
}
toolchain/parser/testdata/if_expression/fail_else_expr_missing.carbon
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'n'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'NameReference', text: 'true'},
// CHECK:STDOUT: {kind: 'IfExpressionThen', text: 'then'},
// CHECK:STDOUT: {kind: 'Literal', text: '1'},
// CHECK:STDOUT: {kind: 'IfExpressionElse', text: 'else'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', has_error: yes, subtree_size: 6},
// CHECK:STDOUT: {kind: 'VariableDeclaration', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_else_expr_missing.carbon:[[@LINE+1]]:35: Expected expression.
var n: i32 = if true then 1 else;
}
toolchain/parser/testdata/if_expression/fail_else_missing.carbon
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+31
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'n'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'NameReference', text: 'true'},
// CHECK:STDOUT: {kind: 'IfExpressionThen', text: 'then'},
// CHECK:STDOUT: {kind: 'Literal', text: '1'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', has_error: yes, subtree_size: 6},
// CHECK:STDOUT: {kind: 'VariableDeclaration', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_else_missing.carbon:[[@LINE+1]]:30: Expected `else` after `if ... then ...`.
var n: i32 = if true then 1;
}
toolchain/parser/testdata/if_expression/fail_then_expr_missing.carbon
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+31
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'n'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'NameReference', text: 'true'},
// CHECK:STDOUT: {kind: 'IfExpressionThen', text: 'then'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', has_error: yes, subtree_size: 6},
// CHECK:STDOUT: {kind: 'VariableDeclaration', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_then_expr_missing.carbon:[[@LINE+1]]:28: Expected expression.
var n: i32 = if true then;
}
toolchain/parser/testdata/if_expression/fail_then_missing.carbon
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+31
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@@ -0,0 +1,31 @@
// 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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'VariableIntroducer', text: 'var'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'n'},
// CHECK:STDOUT: {kind: 'Literal', text: 'i32'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'VariableInitializer', text: '='},
// CHECK:STDOUT: {kind: 'NameReference', text: 'true'},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: ';', has_error: yes},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', has_error: yes, subtree_size: 6},
// CHECK:STDOUT: {kind: 'VariableDeclaration', text: ';', subtree_size: 12},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 18},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_then_missing.carbon:[[@LINE+1]]:23: Expected `then` after `if` condition.
var n: i32 = if true;
}
toolchain/parser/testdata/if_expression/fail_top_level_if.carbon
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+29
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 5},
// CHECK:STDOUT: {kind: 'IfConditionStart', text: 'if', has_error: yes},
// CHECK:STDOUT: {kind: 'NameReference', text: 'true'},
// CHECK:STDOUT: {kind: 'IfCondition', text: 'if', has_error: yes, subtree_size: 3},
// CHECK:STDOUT: {kind: 'CodeBlockStart', text: 'then', has_error: yes},
// CHECK:STDOUT: {kind: 'InvalidParse', text: 'then', has_error: yes},
// CHECK:STDOUT: {kind: 'ExpressionStatement', text: ';', has_error: yes, subtree_size: 2},
// CHECK:STDOUT: {kind: 'CodeBlock', text: 'then', has_error: yes, subtree_size: 4},
// CHECK:STDOUT: {kind: 'IfStatement', text: 'if', subtree_size: 8},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 14},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F() {
// CHECK:STDERR: fail_top_level_if.carbon:[[@LINE+3]]:6: Expected `(` after `if`.
// CHECK:STDERR: fail_top_level_if.carbon:[[@LINE+2]]:11: Expected braced code block.
// CHECK:STDERR: fail_top_level_if.carbon:[[@LINE+1]]:11: Expected expression.
if true then 1 else 2;
}
toolchain/parser/testdata/if_expression/precedence.carbon
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+37
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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
// CHECK:STDOUT: [
// CHECK:STDOUT: {kind: 'FunctionIntroducer', text: 'fn'},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'F'},
// CHECK:STDOUT: {kind: 'ParameterListStart', text: '('},
// CHECK:STDOUT: {kind: 'DeclaredName', text: 'b'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'bool'},
// CHECK:STDOUT: {kind: 'PatternBinding', text: ':', subtree_size: 3},
// CHECK:STDOUT: {kind: 'ParameterList', text: ')', subtree_size: 5},
// CHECK:STDOUT: {kind: 'NameReference', text: 'bool'},
// CHECK:STDOUT: {kind: 'ReturnType', text: '->', subtree_size: 2},
// CHECK:STDOUT: {kind: 'FunctionDefinitionStart', text: '{', subtree_size: 10},
// CHECK:STDOUT: {kind: 'ReturnStatementStart', text: 'return'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'InfixOperator', text: 'and', subtree_size: 3},
// CHECK:STDOUT: {kind: 'IfExpressionThen', text: 'then'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'InfixOperator', text: 'and', subtree_size: 3},
// CHECK:STDOUT: {kind: 'IfExpressionElse', text: 'else'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'NameReference', text: 'b'},
// CHECK:STDOUT: {kind: 'InfixOperator', text: 'or', subtree_size: 3},
// CHECK:STDOUT: {kind: 'IfExpression', text: 'if', subtree_size: 12},
// CHECK:STDOUT: {kind: 'ReturnStatement', text: ';', subtree_size: 14},
// CHECK:STDOUT: {kind: 'FunctionDefinition', text: '}', subtree_size: 25},
// CHECK:STDOUT: {kind: 'FileEnd', text: ''},
// CHECK:STDOUT: ]
fn F(b: bool) -> bool {
return if b and b then b and b else b or b;
}