Fix ValidatePrivateFields: UpperFirst corrupts unexported embedded struct field paths

[Copilot]

ValidatePrivateFields = true had no effect because strutil.UpperFirst() was unconditionally applied in TryGet and Set, turning paths like foo.Field1 into Foo.Field1. Since the embedded struct is registered as foo (lowercase), FieldByName("Foo") always failed silently — making validation behave as if the field didn't exist regardless of its value.

The existing test masked this: it asserted hasError == true with an invalid value, which passed — but only because the field was invisible to the validator, not because the rule fired. Setting a valid value still produced errors.

Changes

• data_source.go — TryGet and Set: apply UpperFirst only when the field is not already present in d.fieldNames. Fields registered during parseRulesFromTag (including private embedded struct fields) retain their original casing; exported field name normalization (e.g. "name" → "Name") is preserved as a fallback.

• data_source_test.go — Extend TestValidatePrivateFieldsWhenTrue to assert that validation passes when the embedded field holds a valid value — the case that was previously broken:

// Field1 = 4 violates min:5 — must fail
v := Struct(barz)
v.Validate()
assert.Equal(t, v.hasError, true)

// Field1 = 5 satisfies all rules — must pass (was broken before fix)
barz.foo.Field1 = 5
v = Struct(barz)
v.Validate()
assert.Equal(t, v.hasError, false)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>ValidatePrivateFields 的配置没有效果</issue_title>
<issue_description>我尝试了这个配置ValidatePrivateFields，但其实并没有效果。

然后我检查了源代码里面的单元测试 TestValidatePrivateFieldsWhenTrue，但这个单元测试其实有问题的。

validate/data_source_test.go

Line 289 in e3dc3a4

assert.Equal(t, v.hasError, true)

这一行断言实际上存在问题，我在debug时发现，断言失败是因为根本没有拿到字段的值，由于

validate/data_source.go

Line 531 in e3dc3a4

field = strutil.UpperFirst(field)

这一行的存在，导致拿字段的值的Path是Foo.Field1而不是foo.Field1。

所以在原有的单测下面加

	barz.Field1 = 5
	v = Struct(barz)
	v.Validate()

	assert.Equal(t, v.hasError, false)

期望应该是没有错误，但还是有错误。

是否把

validate/data_source.go

Line 531 in e3dc3a4

field = strutil.UpperFirst(field)

这行删掉即可？</issue_description>

<agent_instructions>找到问题并提供修复PR</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes ValidatePrivateFields 的配置没有效果 #325

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[Copilot]

Pull request overview

Fixes struct field-path normalization so ValidatePrivateFields = true can correctly access validation rules on unexported embedded struct fields (e.g. foo.Field1) without corrupting the path casing.

Changes:

• Adjust StructData.TryGet / StructData.Set to apply UpperFirst only as a fallback when the field path isn’t already registered.
• Extend TestValidatePrivateFieldsWhenTrue to assert the “valid value passes” case that previously failed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
data_source.go	Makes path normalization conditional to preserve original casing for registered (including private embedded) field paths.
data_source_test.go	Adds a regression assertion ensuring validation passes when the embedded field value is valid.

[Copilot]

Set can now skip UpperFirst for registered embedded-field paths (e.g. foo.Field1), but the rest of Set does not handle fieldAtAnonymous (the switch case is empty). If d.fieldNames[field] is fieldAtAnonymous, fv remains an invalid reflect.Value and removeValuePtr(fv) will panic. Consider handling fieldAtAnonymous the same as fieldAtSubStruct (walk the path and select the nested field), or otherwise return a controlled error instead of leaving fv invalid.

[Copilot]

These assertions pass actual then expected to assert.Equal, which is inconsistent with the surrounding tests that use assert.Equal(t, expected, actual) (e.g. data_source_test.go:260-261, issues_test.go:511). Swapping the argument order (or using assert.True/False) will make assertion failures much easier to interpret.