internal/mcp/jsonschema: clearer validations errors

Validation errors now more clearly indicate the path from the root
schema.

- Enhance schema iteration to yield the path, and generalize it by using
  reflection.

- Store each schema's path inside the schema.

- Remove the path arg from validate: we don't need it anymore.

- Improve the test for the iterators and add one for validation
  errors.

Change-Id: Ief55133ef4ae2eac0736208a3b9f78ed69933b31
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676375
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jonathan Amsterdam <jba@google.com>

jsonschema/schema_test.go

@@ -9,6 +9,8 @@ import (
 	"fmt"
 	"math"
 	"regexp"
+	"slices"
+	"strings"
 	"testing"
 )
 
@@ -112,15 +114,31 @@ func TestUnmarshalErrors(t *testing.T) {
 func TestEvery(t *testing.T) {
 	// Schema.every should visit all descendants of a schema, not just the immediate ones.
 	s := &Schema{
-		Items: &Schema{
-			Items: &Schema{},
-		},
+		Type:        "string",
+		PrefixItems: []*Schema{{Type: "int"}, {Items: &Schema{Type: "null"}}},
+		Contains: &Schema{Properties: map[string]*Schema{
+			"~1": {Type: "boolean"},
+			"p":  {},
+		}},
 	}
-	want := 3
-	got := 0
-	s.every(func(*Schema) bool { got++; return true })
-	if got != want {
-		t.Errorf("got %d, want %d", got, want)
+
+	type item struct {
+		s *Schema
+		p string
+	}
+	want := []item{
+		{s, ""},
+		{s.Contains, "contains"},
+		{s.Contains.Properties["p"], "contains/properties/p"},
+		{s.Contains.Properties["~1"], "contains/properties/~01"},
+		{s.PrefixItems[0], "prefixItems/0"},
+		{s.PrefixItems[1], "prefixItems/1"},
+		{s.PrefixItems[1].Items, "prefixItems/1/items"},
+	}
+	var got []item
+	s.every(func(s *Schema, p []string) bool { got = append(got, item{s, strings.Join(p, "/")}); return true }, nil)
+	if !slices.Equal(got, want) {
+		t.Errorf("\n got  %v\nwant %v", got, want)
 	}
 }
 
@@ -130,3 +148,21 @@ func mustUnmarshal(t *testing.T, data []byte, ptr any) {
 		t.Fatal(err)
 	}
 }
+
+// json returns the schema in json format.
+func (s *Schema) json() string {
+	data, err := json.Marshal(s)
+	if err != nil {
+		return fmt.Sprintf("<jsonschema.Schema:%v>", err)
+	}
+	return string(data)
+}
+
+// json returns the schema in json format, indented.
+func (s *Schema) jsonIndent() string {
+	data, err := json.MarshalIndent(s, "", "  ")
+	if err != nil {
+		return fmt.Sprintf("<jsonschema.Schema:%v>", err)
+	}
+	return string(data)
+}