Resolves #54 - Allow reduction of nil AstNode (#55)

external/epsearchast/v3/reduce.go

@@ -7,6 +7,9 @@ package epsearchast_v3
 //
 // Depending on what you are doing you may find that [epsearchast_v3.SemanticReduceAst] to be simpler.
 func ReduceAst[T any](a *AstNode, f func(*AstNode, []*T) (*T, error)) (*T, error) {
+	if a == nil {
+		return nil, nil
+	}
 	collector := make([]*T, 0, len(a.Children))
 	for _, n := range a.Children {
 		v, err := ReduceAst(n, f)

external/epsearchast/v3/reduce_test.go

@@ -0,0 +1,20 @@
+package epsearchast_v3
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestReduceNilAstDoesNotPanic(t *testing.T) {
+	// Fixture Setup
+	var ast *AstNode = nil
+
+	// Execute SUT
+	result, err := ReduceAst(ast, func(*AstNode, []*string) (*string, error) {
+		panic("should not be called")
+	})
+
+	// Verification
+	require.NoError(t, err)
+	require.Nil(t, result)
+}

external/epsearchast/v3/semantic_reduce_test.go

@@ -0,0 +1,71 @@
+package epsearchast_v3
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestSemanticReduceNilAstDoesNotPanic(t *testing.T) {
+	// Fixture Setup
+	var ast *AstNode = nil
+
+	// Execute SUT
+	reducer := PanicyReducer{}
+
+	result, err := SemanticReduceAst(ast, reducer)
+
+	// Verification
+	require.NoError(t, err)
+	require.Nil(t, result)
+}
+
+type PanicyReducer struct {
+}
+
+func (p PanicyReducer) PostVisitAnd(rs []*string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitIn(args ...string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitEq(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitLe(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitLt(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitGe(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitGt(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitLike(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitILike(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitContains(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitText(first, second string) (*string, error) {
+	panic("not called")
+}
+
+func (p PanicyReducer) VisitIsNull(first string) (*string, error) {
+	panic("not called")
+}