[slang][parser] Fix timeless constraint expression parsing (#1128)

source/parsing/Parser_members.cpp

@@ -2206,10 +2206,15 @@ ConstraintItemSyntax* Parser::parseConstraintItem(bool allowBlock, bool isTopLev
     if (!isPossibleExpression(peek().kind) && !allowBlock)
         return nullptr;
 
+    Token curr = peek();
     // at this point we either have an expression with optional distribution or
     // we have an implication constraint
     auto expr =
         &parseSubExpression(ExpressionOptions::ConstraintContext | ExpressionOptions::AllowDist, 0);
+    // checking that tokens were extracted during expression parsing
+    if (curr == peek() && !allowBlock)
+        return nullptr;
+
     if (peek(TokenKind::MinusArrow)) {
         auto arrow = consume();
         return &factory.implicationConstraint(*expr, arrow, *parseConstraintItem(true, false));

source/parsing/Parser_statements.cpp

@@ -762,14 +762,14 @@ RandCaseStatementSyntax& Parser::parseRandCaseStatement(NamedLabelSyntax* label,
     SmallVector<RandCaseItemSyntax*> itemBuffer;
 
     while (isPossibleExpression(peek().kind)) {
+        Token curr = peek();
         auto& expr = parseExpression();
         auto colon = expect(TokenKind::Colon);
-        const auto loc = peek().location();
         auto& stmt = parseStatement();
-        if (stmt.kind == SyntaxKind::EmptyStatement &&
-            stmt.as<EmptyStatementSyntax>().semicolon.isMissing() && loc == peek().location()) {
+        // If there is no consumed tokens then expression and statement were not parsed
+        if (curr == peek())
             skipToken(std::nullopt);
-        }
+
         itemBuffer.push_back(&factory.randCaseItem(expr, colon, stmt));
     }
 
@@ -995,8 +995,13 @@ StatementSyntax& Parser::parseRandSequenceStatement(NamedLabelSyntax* label, Att
     auto closeParen = expect(TokenKind::CloseParenthesis);
 
     SmallVector<ProductionSyntax*> productions;
-    while (isPossibleDataType(peek().kind))
+    while (isPossibleDataType(peek().kind)) {
+        Token curr = peek();
         productions.push_back(&parseProduction());
+        // If there is no consumed tokens then production was not parsed
+        if (curr == peek())
+            skipToken(std::nullopt);
+    }
 
     if (productions.empty())
         addDiag(diag::ExpectedRsRule, peek().location());

tests/unittests/parsing/MemberParsingTests.cpp

@@ -1489,3 +1489,22 @@ endmodule
     REQUIRE(diagnostics.size() == 1);
     CHECK(diagnostics[0].code == diag::UnexpectedEndDelim);
 }
+
+TEST_CASE("Bad top level constraints") {
+    auto& text = R"(
+constraint A :: A { &&& }
+
+constraint A :: A { matches }
+
+constraint A :: A { soft *) 0 ; }
+
+program A ; final randsequence ( const ) A : A ; endsequence endprogram
+
+constraint A :: A { foreach ( &&& A [ ] ) 0 ; }
+
+program A ; final randcase 0 : matches A = # 0 0 ; endcase endprogram
+)";
+    parseCompilationUnit(text);
+
+    REQUIRE(diagnostics.size() == 16);
+}