4 files changed, 80 insertions, 5 deletions

diff --git a/Userland/Libraries/LibSQL/AST.h b/Userland/Libraries/LibSQL/AST.h
index 922432b48a..96f0e970dc 100644
--- a/Userland/Libraries/LibSQL/AST.h
+++ b/Userland/Libraries/LibSQL/AST.h
@@ -537,6 +537,22 @@ private:
     RefPtr<Expression> m_else_expression;
 };
 
+class ExistsExpression : public Expression {
+public:
+    ExistsExpression(NonnullRefPtr<Select> select_statement, bool invert_expression)
+        : m_select_statement(move(select_statement))
+        , m_invert_expression(invert_expression)
+    {
+    }
+
+    const NonnullRefPtr<Select>& select_statement() const { return m_select_statement; }
+    bool invert_expression() const { return m_invert_expression; }
+
+private:
+    NonnullRefPtr<Select> m_select_statement;
+    bool m_invert_expression;
+};
+
 class CollateExpression : public NestedExpression {
 public:
     CollateExpression(NonnullRefPtr<Expression> expression, String collation_name)
diff --git a/Userland/Libraries/LibSQL/Parser.cpp b/Userland/Libraries/LibSQL/Parser.cpp
index 69b30e37ad..8775c2d3b3 100644
--- a/Userland/Libraries/LibSQL/Parser.cpp
+++ b/Userland/Libraries/LibSQL/Parser.cpp
@@ -215,7 +215,6 @@ NonnullRefPtr<Expression> Parser::parse_expression()
 
     // FIXME: Parse 'bind-parameter'.
     // FIXME: Parse 'function-name'.
-    // FIXME: Parse 'exists'.
     // FIXME: Parse 'raise-function'.
 
     return expression;
@@ -241,6 +240,9 @@ NonnullRefPtr<Expression> Parser::parse_primary_expression()
     if (auto expression = parse_case_expression(); expression.has_value())
         return move(expression.value());
 
+    if (auto expression = parse_exists_expression(false); expression.has_value())
+        return move(expression.value());
+
     expected("Primary Expression");
     consume();
 
@@ -381,8 +383,12 @@ Optional<NonnullRefPtr<Expression>> Parser::parse_unary_operator_expression()
     if (consume_if(TokenType::Tilde))
         return create_ast_node<UnaryOperatorExpression>(UnaryOperator::BitwiseNot, parse_expression());
 
-    if (consume_if(TokenType::Not))
-        return create_ast_node<UnaryOperatorExpression>(UnaryOperator::Not, parse_expression());
+    if (consume_if(TokenType::Not)) {
+        if (match(TokenType::Exists))
+            return parse_exists_expression(true);
+        else
+            return create_ast_node<UnaryOperatorExpression>(UnaryOperator::Not, parse_expression());
+    }
 
     return {};
 }
@@ -448,11 +454,15 @@ Optional<NonnullRefPtr<Expression>> Parser::parse_binary_operator_expression(Non
 
 Optional<NonnullRefPtr<Expression>> Parser::parse_chained_expression()
 {
-    if (!match(TokenType::ParenOpen))
+    if (!consume_if(TokenType::ParenOpen))
         return {};
 
+    if (match(TokenType::Select))
+        return parse_exists_expression(false, TokenType::Select);
+
     NonnullRefPtrVector<Expression> expressions;
-    parse_comma_separated_list(true, [&]() { expressions.append(parse_expression()); });
+    parse_comma_separated_list(false, [&]() { expressions.append(parse_expression()); });
+    consume(TokenType::ParenClose);
 
     return create_ast_node<ChainedExpression>(move(expressions));
 }
@@ -506,6 +516,21 @@ Optional<NonnullRefPtr<Expression>> Parser::parse_case_expression()
     return create_ast_node<CaseExpression>(move(case_expression), move(when_then_clauses), move(else_expression));
 }
 
+Optional<NonnullRefPtr<Expression>> Parser::parse_exists_expression(bool invert_expression, TokenType opening_token)
+{
+    VERIFY((opening_token == TokenType::Exists) || (opening_token == TokenType::Select));
+
+    if ((opening_token == TokenType::Exists) && !consume_if(TokenType::Exists))
+        return {};
+
+    if (opening_token == TokenType::Exists)
+        consume(TokenType::ParenOpen);
+    auto select_statement = parse_select_statement({});
+    consume(TokenType::ParenClose);
+
+    return create_ast_node<ExistsExpression>(move(select_statement), invert_expression);
+}
+
 Optional<NonnullRefPtr<Expression>> Parser::parse_collate_expression(NonnullRefPtr<Expression> expression)
 {
     if (!match(TokenType::Collate))
diff --git a/Userland/Libraries/LibSQL/Parser.h b/Userland/Libraries/LibSQL/Parser.h
index 6d6cf91591..14b03bbf52 100644
--- a/Userland/Libraries/LibSQL/Parser.h
+++ b/Userland/Libraries/LibSQL/Parser.h
@@ -68,6 +68,7 @@ private:
     Optional<NonnullRefPtr<Expression>> parse_chained_expression();
     Optional<NonnullRefPtr<Expression>> parse_cast_expression();
     Optional<NonnullRefPtr<Expression>> parse_case_expression();
+    Optional<NonnullRefPtr<Expression>> parse_exists_expression(bool invert_expression, TokenType opening_token = TokenType::Exists);
     Optional<NonnullRefPtr<Expression>> parse_collate_expression(NonnullRefPtr<Expression> expression);
     Optional<NonnullRefPtr<Expression>> parse_is_expression(NonnullRefPtr<Expression> expression);
     Optional<NonnullRefPtr<Expression>> parse_match_expression(NonnullRefPtr<Expression> lhs, bool invert_expression);
diff --git a/Userland/Libraries/LibSQL/Tests/TestSqlExpressionParser.cpp b/Userland/Libraries/LibSQL/Tests/TestSqlExpressionParser.cpp
index 4d8952dc14..1e7a2ef187 100644
--- a/Userland/Libraries/LibSQL/Tests/TestSqlExpressionParser.cpp
+++ b/Userland/Libraries/LibSQL/Tests/TestSqlExpressionParser.cpp
@@ -338,6 +338,39 @@ TEST_CASE(case_expression)
     validate("CASE 15 WHEN 16 THEN 17 WHEN 18 THEN 19 ELSE 20 END", true, 2, true);
 }
 
+TEST_CASE(exists_expression)
+{
+    EXPECT(parse("EXISTS").is_error());
+    EXPECT(parse("EXISTS (").is_error());
+    EXPECT(parse("EXISTS (SELECT").is_error());
+    EXPECT(parse("EXISTS (SELECT)").is_error());
+    EXPECT(parse("EXISTS (SELECT * FROM table").is_error());
+    EXPECT(parse("NOT EXISTS").is_error());
+    EXPECT(parse("NOT EXISTS (").is_error());
+    EXPECT(parse("NOT EXISTS (SELECT").is_error());
+    EXPECT(parse("NOT EXISTS (SELECT)").is_error());
+    EXPECT(parse("NOT EXISTS (SELECT * FROM table").is_error());
+    EXPECT(parse("(").is_error());
+    EXPECT(parse("(SELECT").is_error());
+    EXPECT(parse("(SELECT)").is_error());
+    EXPECT(parse("(SELECT * FROM table").is_error());
+
+    auto validate = [](StringView sql, bool expected_invert_expression) {
+        auto result = parse(sql);
+        EXPECT(!result.is_error());
+
+        auto expression = result.release_value();
+        EXPECT(is<SQL::ExistsExpression>(*expression));
+
+        const auto& exists = static_cast<const SQL::ExistsExpression&>(*expression);
+        EXPECT_EQ(exists.invert_expression(), expected_invert_expression);
+    };
+
+    validate("EXISTS (SELECT * FROM table)", false);
+    validate("NOT EXISTS (SELECT * FROM table)", true);
+    validate("(SELECT * FROM table)", false);
+}
+
 TEST_CASE(collate_expression)
 {
     EXPECT(parse("COLLATE").is_error());