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Add sentinel precedence levels for the top-level expression context and (#465)

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for an expression with no operators.
This commit is contained in:
Richard Smith
2021-04-15 18:57:28 -07:00
committed by GitHub
parent 09763653b7
commit 1ee826268c
4 changed files with 56 additions and 15 deletions
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parser/parser_impl.cpp
+10 -13
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@@ -593,12 +593,11 @@ auto ParseTree::Parser::ParsePostfixExpression() -> llvm::Optional<Node> {
}
auto ParseTree::Parser::ParseOperatorExpression(
llvm::Optional<PrecedenceGroup> ambient_precedence)
-> llvm::Optional<Node> {
PrecedenceGroup ambient_precedence) -> llvm::Optional<Node> {
auto start = StartSubtree();
llvm::Optional<Node> lhs;
llvm::Optional<PrecedenceGroup> lhs_precedence;
PrecedenceGroup lhs_precedence = PrecedenceGroup::ForPostfixExpression();
// Check for a prefix operator.
if (auto operator_precedence =
@@ -606,9 +605,9 @@ auto ParseTree::Parser::ParseOperatorExpression(
!operator_precedence) {
lhs = ParsePostfixExpression();
} else {
if (ambient_precedence && PrecedenceGroup::GetPriority(
*ambient_precedence, *operator_precedence) !=
OperatorPriority::RightFirst) {
if (PrecedenceGroup::GetPriority(ambient_precedence,
*operator_precedence) !=
OperatorPriority::RightFirst) {
// The precedence rules don't permit this prefix operator in this
// context. Diagnose this, but carry on and parse it anyway.
emitter.EmitError<OperatorRequiresParentheses>(*position);
@@ -625,17 +624,15 @@ auto ParseTree::Parser::ParseOperatorExpression(
while (auto trailing_operator =
PrecedenceGroup::ForTrailing(tokens.GetKind(*position))) {
auto [operator_precedence, is_binary] = *trailing_operator;
if (ambient_precedence && PrecedenceGroup::GetPriority(
*ambient_precedence, operator_precedence) !=
OperatorPriority::RightFirst) {
if (PrecedenceGroup::GetPriority(ambient_precedence, operator_precedence) !=
OperatorPriority::RightFirst) {
// The precedence rules don't permit this operator in this context. Try
// again in the enclosing expression context.
return lhs;
}
if (lhs_precedence &&
PrecedenceGroup::GetPriority(*lhs_precedence, operator_precedence) !=
OperatorPriority::LeftFirst) {
if (PrecedenceGroup::GetPriority(lhs_precedence, operator_precedence) !=
OperatorPriority::LeftFirst) {
// Either the LHS operator and this operator are ambiguous, or the
// LHS operaor is a unary operator that can't be nested within
// this operator. Either way, parentheses are required.
@@ -660,7 +657,7 @@ auto ParseTree::Parser::ParseOperatorExpression(
}
auto ParseTree::Parser::ParseExpression() -> llvm::Optional<Node> {
return ParseOperatorExpression(llvm::None);
return ParseOperatorExpression(PrecedenceGroup::ForTopLevelExpression());
}
auto ParseTree::Parser::ParseExpressionStatement() -> llvm::Optional<Node> {