Fix issue where unexported fields where skipped

By default, the linter only checks exported (uppercase) fields in Equals()
methods. This leaves structs with private fields completely unchecked.

Add a new checkUnexported config option (default: false) that enables
linting of unexported fields as well. This is useful for internal types
like policy IR structs that use lowercase field names."

Signed-off-by: timflannagan <timflannagan@gmail.com>

Author: timflannagan

README.md

@@ -39,7 +39,8 @@ linters-settings:
       type: "module"
       description: "Checks Equals() implementations for KRT-style semantic equality issues"
       settings:
-        deepEqual: true  # Enable reflect.DeepEqual detection (optional)
+        deepEqual: true       # Enable reflect.DeepEqual detection (optional)
+        checkUnexported: true # Check unexported (lowercase) fields (optional)
 ```
 
 ### Programmatic Usage
@@ -52,15 +53,18 @@ a := analyzer.Analyzer
 
 // Or create a custom configured analyzer
 a := analyzer.NewAnalyzer(&analyzer.Config{
-    DeepEqual: true,
+    DeepEqual:       true,
+    CheckUnexported: true,
 })
 ```
 
 ## What It Checks
 
 ### Missing Field Comparisons
 
-The analyzer ensures that all exported fields of a struct are used in its `Equals()` method. If a field is not compared, it could lead to incorrect equality results.
+By default, the analyzer ensures that all exported fields of a struct are used in its `Equals()` method. If a field is not compared, it could lead to incorrect equality results.
+
+When `checkUnexported: true` is enabled, unexported (lowercase) fields are also checked. This is useful for structs with private fields that should still participate in equality comparisons.
 
 ```go
 type MyStruct struct {
@@ -116,6 +120,7 @@ type MyStruct struct {
 | Option | Type | Default | Description |
 |--------|------|---------|-------------|
 | `deepEqual` | bool | `false` | Enable detection of `reflect.DeepEqual` usage in `Equals()` methods |
+| `checkUnexported` | bool | `false` | Check unexported (lowercase) fields in addition to exported fields |
 
 ## Project Structure
 

pkg/analyzer/analyzer.go

@@ -18,6 +18,10 @@ type Config struct {
 	// DeepEqual toggles the rule that flags usage of reflect.DeepEqual inside Equals methods.
 	// This check is disabled by default for incremental rollout.
 	DeepEqual bool `json:"deepEqual"`
+	// CheckUnexported toggles whether unexported (lowercase) fields are checked.
+	// By default, only exported fields are validated. Enable this to also check
+	// that unexported fields are used in Equals methods.
+	CheckUnexported bool `json:"checkUnexported"`
 }
 
 // Analyzer is the default analyzer instance with all checks disabled.
@@ -100,7 +104,11 @@ func (a *analyzerImpl) Run(pass *analysis.Pass) (any, error) {
 			return
 		}
 		for _, f := range sinfo.fields {
-			if !f.exported || f.ignore || f.todo {
+			if f.ignore || f.todo {
+				continue
+			}
+			// Skip unexported fields unless checkUnexported is enabled
+			if !f.exported && !a.cfg.CheckUnexported {
 				continue
 			}
 			if !usedFields[f.name] {

pkg/analyzer/analyzer_test.go

@@ -41,3 +41,15 @@ func TestMethodArgs(t *testing.T) {
 	a := NewAnalyzer(&Config{})
 	analysistest.Run(t, testdata, a, "methodargs")
 }
+
+func TestUnexportedCheckEnabled(t *testing.T) {
+	testdata := analysistest.TestData()
+	a := NewAnalyzer(&Config{CheckUnexported: true})
+	analysistest.Run(t, testdata, a, "unexportedon")
+}
+
+func TestUnexportedCheckDisabled(t *testing.T) {
+	testdata := analysistest.TestData()
+	a := NewAnalyzer(&Config{CheckUnexported: false})
+	analysistest.Run(t, testdata, a, "unexportedoff")
+}

pkg/analyzer/testdata/src/unexportedoff/unexported.go

@@ -0,0 +1,39 @@
+package unexportedoff
+
+// UnexportedFields has only unexported fields.
+// When checkUnexported is disabled (default), no errors should be reported.
+type UnexportedFields struct {
+	name    string
+	value   int
+	missing bool
+}
+
+func (u *UnexportedFields) Equals(other *UnexportedFields) bool {
+	if u == nil && other == nil {
+		return true
+	}
+	if u == nil || other == nil {
+		return false
+	}
+	// Only comparing name and value, missing is not used.
+	// But since checkUnexported is off, no error should be reported.
+	return u.name == other.name && u.value == other.value
+}
+
+// MixedFields has both exported and unexported fields.
+type MixedFields struct {
+	Name     string
+	internal int
+	Missing  string // want "field \"Missing\" in type \"MixedFields\" is not used in Equals"
+}
+
+func (m *MixedFields) Equals(other *MixedFields) bool {
+	if m == nil && other == nil {
+		return true
+	}
+	if m == nil || other == nil {
+		return false
+	}
+	// Only exported Name is checked when checkUnexported is off
+	return m.Name == other.Name && m.internal == other.internal
+}

pkg/analyzer/testdata/src/unexportedon/unexported.go

@@ -0,0 +1,55 @@
+package unexportedon
+
+// UnexportedFields has only unexported fields.
+// When checkUnexported is enabled, missing unexported fields should be flagged.
+type UnexportedFields struct {
+	name    string
+	value   int
+	missing bool // want "field \"missing\" in type \"UnexportedFields\" is not used in Equals"
+}
+
+func (u *UnexportedFields) Equals(other *UnexportedFields) bool {
+	if u == nil && other == nil {
+		return true
+	}
+	if u == nil || other == nil {
+		return false
+	}
+	return u.name == other.name && u.value == other.value
+}
+
+// MixedFields has both exported and unexported fields.
+type MixedFields struct {
+	Name            string
+	internal        int
+	missingInternal int    // want "field \"missingInternal\" in type \"MixedFields\" is not used in Equals"
+	Missing         string // want "field \"Missing\" in type \"MixedFields\" is not used in Equals"
+}
+
+func (m *MixedFields) Equals(other *MixedFields) bool {
+	if m == nil && other == nil {
+		return true
+	}
+	if m == nil || other == nil {
+		return false
+	}
+	return m.Name == other.Name && m.internal == other.internal
+}
+
+// AllFieldsUsed should pass with no errors when all fields are compared.
+type AllFieldsUsed struct {
+	name  string
+	value int
+	extra bool
+}
+
+func (a *AllFieldsUsed) Equals(other *AllFieldsUsed) bool {
+	if a == nil && other == nil {
+		return true
+	}
+	if a == nil || other == nil {
+		return false
+	}
+	return a.name == other.name && a.value == other.value && a.extra == other.extra
+}
+