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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/parser_context.cpp
+8 -5
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@@ -313,6 +313,11 @@ auto ParserContext::IsTrailingOperatorInfix() -> bool {
}
auto ParserContext::DiagnoseOperatorFixity(OperatorFixity fixity) -> void {
if (!PositionKind().is_symbol()) {
// Whitespace-based fixity rules only apply to symbolic operators.
return;
}
if (fixity == OperatorFixity::Infix) {
// Infix operators must satisfy the infix operator rules.
if (!IsLexicallyValidInfixOperator()) {
@@ -331,8 +336,7 @@ auto ParserContext::DiagnoseOperatorFixity(OperatorFixity fixity) -> void {
// Whitespace is not permitted between a symbolic pre/postfix operator and
// its operand.
if (PositionKind().is_symbol() &&
(prefix ? tokens().HasTrailingWhitespace(*position_)
if ((prefix ? tokens().HasTrailingWhitespace(*position_)
: tokens().HasLeadingWhitespace(*position_))) {
CARBON_DIAGNOSTIC(UnaryOperatorHasWhitespace, Error,
"Whitespace is not allowed {0} this unary operator.",
@@ -340,9 +344,8 @@ auto ParserContext::DiagnoseOperatorFixity(OperatorFixity fixity) -> void {
emitter_->Emit(
*position_, UnaryOperatorHasWhitespace,
prefix ? RelativeLocation::After : RelativeLocation::Before);
}
// Pre/postfix operators must not satisfy the infix operator rules.
if (IsLexicallyValidInfixOperator()) {
} else if (IsLexicallyValidInfixOperator()) {
// Pre/postfix operators must not satisfy the infix operator rules.
CARBON_DIAGNOSTIC(UnaryOperatorRequiresWhitespace, Error,
"Whitespace is required {0} this unary operator.",
RelativeLocation);