Fix 25 todo tests: CAST alias, inf/nan formatting, subquery alias, named tuples

Key fixes:
- Add UsedASSyntax field to CastExpr to distinguish CAST(x AS Type) from CAST(x, 'Type')
- Fix inf/nan float formatting to use lowercase (inf, -inf, nan) matching ClickHouse
- Add NameTypePair support in FormatDataType for named tuple fields like Tuple(a UInt32)
- Display Subquery alias when present
- Update 03601 golden file for inf formatting change

Tests now passing:
- 00503_cast_const_nullable
- 00516_is_inf_nan
- 00525_aggregate_functions_of_nullable_that_return_non_nullable
- 00547_named_tuples
- 01351_geohash_assert
- 01581_to_int_inf_nan
- 01602_modified_julian_day_msan
- 01611_constant_folding_subqueries
- 01642_if_nullable_regression
- 01664_decimal_ubsan
- 01677_bit_float
- 01679_format_readable_time_delta_inf
- 01773_datetime64_add_ubsan
- 01852_cast_operator
- 02007_ipv4_and_ipv6_to_and_from_string
- 02136_scalar_subquery_metrics
- 02148_cast_type_parsing
- 02313_avro_records_and_maps
- 02366_union_decimal_conversion
- 02416_input_json_formats
- 02795_full_join_assert_cast
- 02832_transform_fixed_string_no_default
- 02921_bit_hamming_distance_big_int
- 03237_get_subcolumn_low_cardinality_column
- 03261_json_hints_types_check

Author: claude

ast/ast.go

@@ -911,6 +911,7 @@ type CastExpr struct {
 	TypeExpr       Expression     `json:"type_expr,omitempty"` // For dynamic type like CAST(x, if(cond, 'Type1', 'Type2'))
 	Alias          string         `json:"alias,omitempty"`
 	OperatorSyntax bool           `json:"operator_syntax,omitempty"` // true if using :: syntax
+	UsedASSyntax   bool           `json:"-"`                         // true if CAST(x AS Type) syntax used (not CAST(x, 'Type'))
 }
 
 func (c *CastExpr) Pos() token.Position { return c.Position }

internal/explain/expressions.go

@@ -198,7 +198,11 @@ func explainUnaryExpr(sb *strings.Builder, n *ast.UnaryExpr, indent string, dept
 
 func explainSubquery(sb *strings.Builder, n *ast.Subquery, indent string, depth int) {
 	children := 1
-	fmt.Fprintf(sb, "%sSubquery (children %d)\n", indent, children)
+	if n.Alias != "" {
+		fmt.Fprintf(sb, "%sSubquery (alias %s) (children %d)\n", indent, n.Alias, children)
+	} else {
+		fmt.Fprintf(sb, "%sSubquery (children %d)\n", indent, children)
+	}
 	Node(sb, n.Query, depth+1)
 }
 
@@ -270,8 +274,12 @@ func explainAliasedExpr(sb *strings.Builder, n *ast.AliasedExpr, depth int) {
 		Node(sb, e.Then, depth+2)
 		Node(sb, e.Else, depth+2)
 	case *ast.CastExpr:
-		// CAST expressions - ClickHouse doesn't show aliases on CAST in EXPLAIN AST
-		explainCastExpr(sb, e, indent, depth)
+		// CAST expressions - show alias only for CAST(x AS Type) syntax, not CAST(x, 'Type')
+		if e.UsedASSyntax {
+			explainCastExprWithAlias(sb, e, n.Alias, indent, depth)
+		} else {
+			explainCastExpr(sb, e, indent, depth)
+		}
 	case *ast.ArrayAccess:
 		// Array access - ClickHouse doesn't show aliases on arrayElement in EXPLAIN AST
 		explainArrayAccess(sb, e, indent, depth)

internal/explain/format.go

@@ -2,6 +2,7 @@ package explain
 
 import (
 	"fmt"
+	"math"
 	"strconv"
 	"strings"
 
@@ -10,6 +11,16 @@ import (
 
 // FormatFloat formats a float value for EXPLAIN AST output
 func FormatFloat(val float64) string {
+	// Handle special float values - ClickHouse uses lowercase
+	if math.IsInf(val, 1) {
+		return "inf"
+	}
+	if math.IsInf(val, -1) {
+		return "-inf"
+	}
+	if math.IsNaN(val) {
+		return "nan"
+	}
 	// Use 'f' format to avoid scientific notation, -1 precision for smallest representation
 	return strconv.FormatFloat(val, 'f', -1, 64)
 }
@@ -161,6 +172,9 @@ func FormatDataType(dt *ast.DataType) string {
 			}
 		} else if nested, ok := p.(*ast.DataType); ok {
 			params = append(params, FormatDataType(nested))
+		} else if ntp, ok := p.(*ast.NameTypePair); ok {
+			// Named tuple field: "name Type"
+			params = append(params, ntp.Name+" "+FormatDataType(ntp.Type))
 		} else {
 			params = append(params, fmt.Sprintf("%v", p))
 		}

internal/explain/functions.go

@@ -83,8 +83,19 @@ func explainCastExpr(sb *strings.Builder, n *ast.CastExpr, indent string, depth
 }
 
 func explainCastExprWithAlias(sb *strings.Builder, n *ast.CastExpr, alias string, indent string, depth int) {
+	// For :: operator syntax, ClickHouse hides alias only when expression is
+	// an array/tuple with complex content that gets formatted as string
+	hideAlias := false
+	if n.OperatorSyntax {
+		if lit, ok := n.Expr.(*ast.Literal); ok {
+			if lit.Type == ast.LiteralArray || lit.Type == ast.LiteralTuple {
+				hideAlias = !containsOnlyPrimitives(lit)
+			}
+		}
+	}
+
 	// CAST is represented as Function CAST with expr and type as arguments
-	if alias != "" {
+	if alias != "" && !hideAlias {
 		fmt.Fprintf(sb, "%sFunction CAST (alias %s) (children %d)\n", indent, alias, 1)
 	} else {
 		fmt.Fprintf(sb, "%sFunction CAST (children %d)\n", indent, 1)

parser/expression.go

@@ -958,6 +958,7 @@ func (p *Parser) parseCast() ast.Expression {
 	if p.currentIs(token.AS) {
 		p.nextToken()
 		expr.Type = p.parseDataType()
+		expr.UsedASSyntax = true
 	} else if p.currentIs(token.COMMA) {
 		p.nextToken()
 		// Type can be given as a string literal or an expression (e.g., if(cond, 'Type1', 'Type2'))
@@ -1564,6 +1565,18 @@ func (p *Parser) parseAlias(left ast.Expression) ast.Expression {
 	case *ast.Subquery:
 		e.Alias = alias
 		return e
+	case *ast.CastExpr:
+		// For :: operator syntax, set alias directly on CastExpr
+		// For function-style CAST(), wrap in AliasedExpr
+		if e.OperatorSyntax {
+			e.Alias = alias
+			return e
+		}
+		return &ast.AliasedExpr{
+			Position: left.Pos(),
+			Expr:     left,
+			Alias:    alias,
+		}
 	case *ast.CaseExpr:
 		e.Alias = alias
 		return e

parser/testdata/00503_cast_const_nullable/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/00516_is_inf_nan/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/00525_aggregate_functions_of_nullable_that_return_non_nullable/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/00547_named_tuples/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/01351_geohash_assert/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}