From 4e9d520c2e46a1fcc54077bc41c4c4dd7cbd8d23 Mon Sep 17 00:00:00 2001
From: Jonathan Amsterdam <jba@google.com>
Date: Tue, 27 May 2025 07:32:06 -0400
Subject: [PATCH] internal/mcp/jsonschema: generalize error wrapping

Add a wrapf function to simplify defers that wrap errors.

Change-Id: If4bedec7d3f56f609d3ca4620aebe7637a59f6bf
Reviewed-on: https://go-review.googlesource.com/c/tools/+/676475
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
---
 jsonschema/json_pointer.go | 6 +-----
 jsonschema/util.go         | 7 +++++++
 jsonschema/validate.go     | 6 +-----
 3 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/jsonschema/json_pointer.go b/jsonschema/json_pointer.go
index 90b4a2c..d7eb4a9 100644
--- a/jsonschema/json_pointer.go
+++ b/jsonschema/json_pointer.go
@@ -69,11 +69,7 @@ func parseJSONPointer(ptr string) (segments []string, err error) {
 // This implementation suffices for JSON Schema: pointers are applied only to Schemas,
 // and refer only to Schemas.
 func dereferenceJSONPointer(s *Schema, sptr string) (_ *Schema, err error) {
-	defer func() {
-		if err != nil {
-			err = fmt.Errorf("JSON Pointer %q: %w", sptr, err)
-		}
-	}()
+	defer wrapf(&err, "JSON Pointer %q", sptr)
 
 	segments, err := parseJSONPointer(sptr)
 	if err != nil {
diff --git a/jsonschema/util.go b/jsonschema/util.go
index 96b32dc..fcb632f 100644
--- a/jsonschema/util.go
+++ b/jsonschema/util.go
@@ -282,3 +282,10 @@ func assert(cond bool, msg string) {
 		panic("assertion failed: " + msg)
 	}
 }
+
+// wrapf wraps *errp with the given formatted message if *errp is not nil.
+func wrapf(errp *error, format string, args ...any) {
+	if *errp != nil {
+		*errp = fmt.Errorf("%s: %w", fmt.Sprintf(format, args...), *errp)
+	}
+}
diff --git a/jsonschema/validate.go b/jsonschema/validate.go
index 634417d..12a6242 100644
--- a/jsonschema/validate.go
+++ b/jsonschema/validate.go
@@ -42,11 +42,7 @@ type state struct {
 
 // validate validates the reflected value of the instance.
 func (st *state) validate(instance reflect.Value, schema *Schema, callerAnns *annotations) (err error) {
-	defer func() {
-		if err != nil {
-			err = fmt.Errorf("%s: %w", schema, err)
-		}
-	}()
+	defer wrapf(&err, "validating %s", schema)
 
 	st.stack = append(st.stack, schema) // push
 	defer func() {