Add AST node validation

compose/internal/repository/ql/ast_nodes.go

@@ -11,6 +11,8 @@ type (
 	ASTNode interface {
 		fmt.Stringer
 		squirrel.Sqlizer
+
+		Validate() error
 	}
 
 	ASTSet   []ASTNode // Stream of comma delimited nodes
@@ -55,20 +57,28 @@ type (
 	}
 )
 
-func (n String) String() string { return fmt.Sprintf("%q", n.Value) }
+func (n String) Validate() (err error) { return }
+func (n String) String() string        { return fmt.Sprintf("%q", n.Value) }
 
-func (n Number) String() string { return n.Value }
+func (n Number) Validate() (err error) { return }
+func (n Number) String() string        { return n.Value }
 
-func (n Operator) String() string { return n.Kind }
+func (n Operator) Validate() (err error) { return }
+func (n Operator) String() string        { return n.Kind }
 
-func (n Keyword) String() string { return n.Keyword }
+func (n Keyword) Validate() (err error) { return }
+func (n Keyword) String() string        { return n.Keyword }
 
-func (n Interval) String() string { return fmt.Sprintf("INTERVAL %s %s", n.Value, n.Unit) }
+func (n Interval) Validate() (err error) { return }
+func (n Interval) String() string        { return fmt.Sprintf("INTERVAL %s %s", n.Value, n.Unit) }
 
-func (n Function) String() string { return fmt.Sprintf("%s(%s)", n.Name, n.Arguments) }
+func (n Function) Validate() (err error) { return }
+func (n Function) String() string        { return fmt.Sprintf("%s(%s)", n.Name, n.Arguments) }
 
-func (n Ident) String() string { return n.Value }
+func (n Ident) Validate() (err error) { return }
+func (n Ident) String() string        { return n.Value }
 
+func (n Column) Validate() (err error) { return }
 func (n Column) String() (out string) {
 	out = n.Expr.String()
 	if n.Alias != "" {
@@ -78,6 +88,29 @@ func (n Column) String() (out string) {
 	return
 }
 
+func (nn ASTNodes) Validate() (err error) {
+	if err = validate(nn); err != nil {
+		return
+	}
+
+	l := len(nn)
+	if l == 0 {
+		return fmt.Errorf("empty set")
+	}
+
+	if op, ok := nn[0].(Operator); ok {
+		return fmt.Errorf("malformed expression, unexpected operator '%s' at first node", op)
+	}
+
+	if l > 1 {
+		if op, ok := nn[l-1].(Operator); ok {
+			return fmt.Errorf("malformed expression, unexpected operator '%s' at last node", op)
+		}
+	}
+
+	return
+}
+
 func (nn ASTNodes) String() (out string) {
 	for _, n := range nn {
 		out = out + n.String()
@@ -86,6 +119,10 @@ func (nn ASTNodes) String() (out string) {
 	return
 }
 
+func (nn ASTSet) Validate() (err error) {
+	return validate(nn)
+}
+
 func (nn ASTSet) String() (out string) {
 	for i, n := range nn {
 		if i > 0 {
@@ -97,6 +134,7 @@ func (nn ASTSet) String() (out string) {
 	return
 }
 
+func (nn Columns) Validate() (err error) { return }
 func (nn Columns) String() (out string) {
 	for i, n := range nn {
 		if i > 0 {
@@ -116,3 +154,17 @@ func (nn Columns) Strings() (out []string) {
 
 	return
 }
+
+func validate(nn []ASTNode) (err error) {
+	if len(nn) == 0 {
+		return fmt.Errorf("empty node set")
+	}
+
+	for _, n := range nn {
+		if err = n.Validate(); err != nil {
+			return
+		}
+	}
+
+	return
+}

compose/internal/repository/ql/ast_nodes_test.go

@@ -0,0 +1,32 @@
+package ql
+
+import (
+	"testing"
+)
+
+// Ensure the parser can parse strings into Statement ASTs.
+func Test_Validators(t *testing.T) {
+	var tests = []struct {
+		tree ASTNode
+	}{
+		{
+			tree: ASTNodes{
+				Ident{Value: "foo"},
+				Operator{Kind: "="},
+			},
+		},
+		{
+			tree: ASTNodes{
+				Operator{Kind: "="},
+				Ident{Value: "foo"},
+			},
+		},
+	}
+
+	for i, test := range tests {
+		if err := test.tree.Validate(); err == nil {
+			t.Fatalf("expecting error, got nil:\n"+
+				"      test case: %d. %q", i, test.tree.String())
+		}
+	}
+}

compose/internal/repository/ql/ast_parser.go

@@ -64,7 +64,7 @@ func (p *Parser) ParseSet(s string) (ASTNode, error) {
 	if set, err := p.parseSet(); err != nil {
 		return nil, err
 	} else {
-		return set, nil
+		return set, set.Validate()
 	}
 }
 
@@ -74,10 +74,11 @@ func (p *Parser) ParseExpression(s string) (ASTNode, error) {
 	if set, err := p.parseExpr(p.nextToken()); err != nil {
 		return nil, err
 	} else if len(set) == 1 {
-		return set[0], nil
+		return set[0], set[0].Validate()
 	} else {
-		return set, nil
+		return set, set.Validate()
 	}
+
 }
 
 func (p *Parser) ParseColumns(s string) (columns Columns, err error) {
@@ -104,6 +105,7 @@ next:
 		goto next
 	}
 
+	err = columns.Validate()
 	return
 }
 

compose/internal/repository/ql/squirrel.go

@@ -49,7 +49,7 @@ func (nn ASTSet) ToSql() (out string, args []interface{}, err error) {
 	return out, args, err
 }
 
-// ToSql returns column alias expression or outpit of underlaying expression's ToSql()
+// ToSql returns column alias expression or output of underlying expression's ToSql()
 func (n Column) ToSql() (string, []interface{}, error) {
 	if n.Alias != "" {
 		return squirrel.Alias(n.Expr, n.Alias).ToSql()