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Update precedence rules to match design. (#3081)

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- Only allow assignment at the top level in an expression statement.
- Allow both negation and complement as subexpressions of both bitwise
  and numeric operators.
- Remove parsing support for postincrement and postdecrement.
- Add parsing support for `as` operator.
- Use the same ambient precedence for types and non-type expressions.

---------

Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
This commit is contained in:
Richard Smith
2023-08-10 18:39:37 +00:00
committed by GitHub
co-authored by Chandler Carruth
parent 3cca175a57
commit fc5a9541ce
18 changed files with 634 additions and 99 deletions
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toolchain/parser/precedence_test.cpp
+8 -22
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@@ -33,29 +33,19 @@ TEST(PrecedenceTest, OperatorsAreRecognized) {
EXPECT_TRUE(PrecedenceGroup::ForTrailing(TokenKind::Minus, true)->is_binary);
EXPECT_FALSE(
PrecedenceGroup::ForTrailing(TokenKind::MinusMinus, false)->is_binary);
PrecedenceGroup::ForTrailing(TokenKind::MinusMinus, false).has_value());
}
TEST(PrecedenceTest, InfixVsPostfix) {
// A trailing `-` is always infix; a trailing `--` is always postfix.
EXPECT_TRUE(PrecedenceGroup::ForTrailing(TokenKind::Minus, false)->is_binary);
EXPECT_FALSE(
PrecedenceGroup::ForTrailing(TokenKind::MinusMinus, true)->is_binary);
// A trailing `-` is always binary, even when written with whitespace that
// suggests it's postfix.
EXPECT_TRUE(PrecedenceGroup::ForTrailing(TokenKind::Minus, /*infix*/ false)
->is_binary);
// A trailing `*` is interpreted based on context.
EXPECT_TRUE(PrecedenceGroup::ForTrailing(TokenKind::Star, true)->is_binary);
EXPECT_FALSE(PrecedenceGroup::ForTrailing(TokenKind::Star, false)->is_binary);
// Postfix `*` can appear in type contexts; infix `*` cannot.
EXPECT_THAT(PrecedenceGroup::GetPriority(
PrecedenceGroup::ForTrailing(TokenKind::Star, true)->level,
PrecedenceGroup::ForType()),
Eq(OperatorPriority::Ambiguous));
EXPECT_THAT(PrecedenceGroup::GetPriority(
PrecedenceGroup::ForTrailing(TokenKind::Star, false)->level,
PrecedenceGroup::ForType()),
Eq(OperatorPriority::LeftFirst));
// Infix `*` can appear in `+` contexts; postfix `*` cannot.
EXPECT_THAT(PrecedenceGroup::GetPriority(
PrecedenceGroup::ForTrailing(TokenKind::Star, true)->level,
@@ -69,18 +59,14 @@ TEST(PrecedenceTest, InfixVsPostfix) {
TEST(PrecedenceTest, Associativity) {
EXPECT_THAT(PrecedenceGroup::ForLeading(TokenKind::Minus)->GetAssociativity(),
Eq(Associativity::None));
EXPECT_THAT(PrecedenceGroup::ForLeading(TokenKind::Star)->GetAssociativity(),
Eq(Associativity::RightToLeft));
EXPECT_THAT(PrecedenceGroup::ForTrailing(TokenKind::PlusPlus, false)
->level.GetAssociativity(),
Eq(Associativity::LeftToRight));
EXPECT_THAT(PrecedenceGroup::ForTrailing(TokenKind::Plus, true)
->level.GetAssociativity(),
Eq(Associativity::LeftToRight));
EXPECT_THAT(PrecedenceGroup::ForTrailing(TokenKind::Equal, true)
->level.GetAssociativity(),
Eq(Associativity::RightToLeft));
EXPECT_THAT(PrecedenceGroup::ForTrailing(TokenKind::PlusEqual, true)
->level.GetAssociativity(),
Eq(Associativity::None));
}
@@ -134,7 +120,7 @@ TEST(PrecedenceTest, IncomparableOperators) {
*PrecedenceGroup::ForLeading(TokenKind::Minus)),
Eq(OperatorPriority::Ambiguous));
EXPECT_THAT(PrecedenceGroup::GetPriority(
*PrecedenceGroup::ForLeading(TokenKind::Minus),
*PrecedenceGroup::ForLeading(TokenKind::Not),
PrecedenceGroup::ForTrailing(TokenKind::Amp, true)->level),
Eq(OperatorPriority::Ambiguous));
EXPECT_THAT(