fix(mysql): Convert boolean literals (true/false) to bool type

Previously, MySQL boolean literals like `SELECT true` were incorrectly
converted to int32 type, while table columns with BOOL/BOOLEAN/TINYINT(1)
types were correctly converted to bool.

The TiDB parser represents boolean literals as mysql.TypeLonglong with
value 1 (true) or 0 (false), which was indistinguishable from integer
literals like `SELECT 1`.

This fix:
- Detects boolean literals by examining the original SQL text
- Converts `true`/`false` (case-insensitive) to bool type
- Preserves integer literals like `SELECT 1` as int32
- Supports all case variations: TRUE, True, FALSE, False, etc.

Test cases:
- SELECT true/false → bool
- SELECT TRUE/FALSE → bool
- SELECT true AS col → bool
- SELECT 1/0 → int32 (unchanged)

Author: kitagry

internal/endtoend/testdata/select_true_literal/mysql/db/db.go

@@ -0,0 +1,11 @@
+-- name: SelectTrue :one
+SELECT true;
+
+-- name: SelectFalse :one
+SELECT false;
+
+-- name: SelectTrueWithAlias :one
+SELECT true AS is_active;
+
+-- name: SelectMultipleBooleans :one
+SELECT true AS col_a, false AS col_b, true AS col_c;

internal/endtoend/testdata/select_true_literal/mysql/db/models.go

@@ -0,0 +1,10 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "db",
+      "engine": "mysql",
+      "queries": "query.sql"
+    }
+  ]
+}

internal/endtoend/testdata/select_true_literal/mysql/db/query.sql.go

@@ -17,6 +17,7 @@ import (
 
 type cc struct {
 	paramCount int
+	sql        string // Original SQL text for this statement
 }
 
 func todo(n pcast.Node) *ast.TODO {
@@ -672,6 +673,41 @@ func (c *cc) convertUpdateStmt(n *pcast.UpdateStmt) *ast.UpdateStmt {
 	return stmt
 }
 
+// isBooleanLiteral checks if the ValueExpr represents a boolean literal (true/false)
+// by examining the original SQL text
+func (c *cc) isBooleanLiteral(n *driver.ValueExpr) bool {
+	if c.sql == "" {
+		return false
+	}
+
+	pos := n.OriginTextPosition()
+	if pos < 0 || pos >= len(c.sql) {
+		return false
+	}
+
+	// Extract the token from the SQL text
+	remaining := strings.ToLower(c.sql[pos:])
+
+	// Check if it starts with "true" or "false" and is followed by a non-identifier character
+	if strings.HasPrefix(remaining, "true") {
+		if len(remaining) == 4 || !isIdentifierChar(remaining[4]) {
+			return true
+		}
+	}
+	if strings.HasPrefix(remaining, "false") {
+		if len(remaining) == 5 || !isIdentifierChar(remaining[5]) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// isIdentifierChar returns true if the character can be part of an identifier
+func isIdentifierChar(c byte) bool {
+	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_'
+}
+
 func (c *cc) convertValueExpr(n *driver.ValueExpr) *ast.A_Const {
 	switch n.TexprNode.Type.GetType() {
 	case mysql.TypeBit:
@@ -691,6 +727,15 @@ func (c *cc) convertValueExpr(n *driver.ValueExpr) *ast.A_Const {
 		mysql.TypeYear,
 		mysql.TypeLong,
 		mysql.TypeLonglong:
+		// Check if this is a boolean literal (true/false)
+		if c.isBooleanLiteral(n) {
+			return &ast.A_Const{
+				Val: &ast.Boolean{
+					Boolval: n.Datum.GetInt64() != 0,
+				},
+				Location: n.OriginTextPosition(),
+			}
+		}
 		return &ast.A_Const{
 			Val: &ast.Integer{
 				Ival: n.Datum.GetInt64(),

internal/endtoend/testdata/select_true_literal/mysql/query.sql

@@ -59,7 +59,7 @@ func (p *Parser) Parse(r io.Reader) ([]ast.Statement, error) {
 	}
 	var stmts []ast.Statement
 	for i := range stmtNodes {
-		converter := &cc{}
+		converter := &cc{sql: string(blob)}
 		out := converter.convert(stmtNodes[i])
 		if _, ok := out.(*ast.TODO); ok {
 			continue