fix(binder): include field name in form/struct bind conversion errors (#2629) (#3005)

bindData had the field name (inputFieldName) in scope but returned bare
conversion errors, so c.Bind() failures gave no indication of which field
failed (e.g. "strconv.ParseInt: parsing \"10a\"..."). Wrap the conversion
errors with the field name using %w so errors.Is/As still work.

Matches the wrap proposed by the reporter in the issue thread. Existing
tests that asserted the bare message are updated to the field-prefixed form.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: vishr

bind.go

@@ -7,6 +7,7 @@ import (
 	"encoding"
 	"encoding/xml"
 	"errors"
+	"fmt"
 	"mime/multipart"
 	"net/http"
 	"reflect"
@@ -249,15 +250,15 @@ func bindData(destination any, data map[string][]string, tag string, dataFiles m
 		// try unmarshalling first, in case we're dealing with an alias to an array type
 		if ok, err := unmarshalInputsToField(typeField.Type.Kind(), inputValue, structField); ok {
 			if err != nil {
-				return err
+				return fmt.Errorf("%s: %w", inputFieldName, err)
 			}
 			continue
 		}
 
 		formatTag := typeField.Tag.Get("format")
 		if ok, err := unmarshalInputToField(typeField.Type.Kind(), inputValue[0], structField, formatTag); ok {
 			if err != nil {
-				return err
+				return fmt.Errorf("%s: %w", inputFieldName, err)
 			}
 			continue
 		}
@@ -275,15 +276,15 @@ func bindData(destination any, data map[string][]string, tag string, dataFiles m
 			slice := reflect.MakeSlice(structField.Type(), numElems, numElems)
 			for j := range numElems {
 				if err := setWithProperType(sliceOf, inputValue[j], slice.Index(j)); err != nil {
-					return err
+					return fmt.Errorf("%s: %w", inputFieldName, err)
 				}
 			}
 			structField.Set(slice)
 			continue
 		}
 
 		if err := setWithProperType(structFieldKind, inputValue[0], structField); err != nil {
-			return err
+			return fmt.Errorf("%s: %w", inputFieldName, err)
 		}
 	}
 	return nil

bind_field_error_test.go

@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: © 2015 LabStack LLC and Echo contributors
+
+package echo
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Regression test for #2629: when binding form data fails a type conversion, the
+// returned error must identify which field failed (so applications can render a
+// useful message), instead of a bare strconv error with no field context.
+func TestBind_formConversionErrorIncludesFieldName(t *testing.T) {
+	e := New()
+	req := httptest.NewRequest(http.MethodPost, "/", strings.NewReader("number=10a"))
+	req.Header.Set(HeaderContentType, MIMEApplicationForm)
+	c := e.NewContext(req, httptest.NewRecorder())
+
+	type DTO struct {
+		Number int `form:"number"`
+	}
+	var dto DTO
+	err := c.Bind(&dto)
+
+	assert.Error(t, err)
+	assert.ErrorContains(t, err, "number", "bind error must identify the failing field")
+}

bind_test.go

@@ -842,7 +842,7 @@ func TestDefaultBinder_BindToStructFromMixedSources(t *testing.T) {
 			givenURL:     "/api/real_node/endpoint?id=nope",
 			givenContent: strings.NewReader(`{"id": 1, "node": "zzz"}`),
 			expect:       &Opts{ID: 0, Node: "node_from_path"}, // path params binding has already modified bind target
-			expectError:  `code=400, message=Bad Request, err=strconv.ParseInt: parsing "nope": invalid syntax`,
+			expectError:  `code=400, message=Bad Request, err=id: strconv.ParseInt: parsing "nope": invalid syntax`,
 		},
 		{
 			name:         "nok, GET body bind failure - trying to bind json array to struct",
@@ -1196,7 +1196,7 @@ func TestBindUnmarshalParamExtras(t *testing.T) {
 		}{}
 		err := testBindURL("/?t=xxxx", &result)
 
-		assert.EqualError(t, err, `code=400, message=Bad Request, err='xxxx' is not an integer`)
+		assert.EqualError(t, err, `code=400, message=Bad Request, err=t: 'xxxx' is not an integer`)
 	})
 
 	t.Run("ok, target is struct", func(t *testing.T) {
@@ -1301,7 +1301,7 @@ func TestBindUnmarshalParams(t *testing.T) {
 		}{}
 		err := testBindURL("/?t=xxxx", &result)
 
-		assert.EqualError(t, err, "code=400, message=Bad Request, err='xxxx' is not an integer")
+		assert.EqualError(t, err, "code=400, message=Bad Request, err=t: 'xxxx' is not an integer")
 	})
 
 	t.Run("ok, target is struct", func(t *testing.T) {
@@ -1368,7 +1368,7 @@ func TestBindInt8(t *testing.T) {
 		}
 		p := target{}
 		err := testBindURL("/?v=x&v=2", &p)
-		assert.EqualError(t, err, `code=400, message=Bad Request, err=strconv.ParseInt: parsing "x": invalid syntax`)
+		assert.EqualError(t, err, `code=400, message=Bad Request, err=v: strconv.ParseInt: parsing "x": invalid syntax`)
 	})
 
 	t.Run("nok, int8 embedded in struct", func(t *testing.T) {