states: fix RootOutputValuesEqual comparing s2 to itself

.changes/v1.15/BUG FIXES-20260214-120000.yaml

@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: 'states: fixed a bug that caused Terraform to be unable to identify when two states had different output values. This may have caused issues in specific circumstances like backend migrations.'
+time: 2026-02-14T12:00:00.000000+00:00
+custom:
+    Issue: "38181"

internal/states/state_equal.go

@@ -101,7 +101,7 @@ func (s *State) RootOutputValuesEqual(s2 *State) bool {
 		return false
 	}
 
-	for k, v1 := range s2.RootOutputValues {
+	for k, v1 := range s.RootOutputValues {
 		v2, ok := s2.RootOutputValues[k]
 		if !ok || !v1.Equal(v2) {
 			return false

internal/states/state_test.go

@@ -474,6 +474,110 @@ func TestStateHasRootOutputValues(t *testing.T) {
 
 }
 
+func TestStateRootOutputValuesEqual(t *testing.T) {
+	tests := map[string]struct {
+		SetupA func(ss *SyncState)
+		SetupB func(ss *SyncState)
+		Want   bool
+	}{
+		"both empty": {
+			func(ss *SyncState) {},
+			func(ss *SyncState) {},
+			true,
+		},
+		"identical outputs": {
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("bar"), false,
+				)
+			},
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("bar"), false,
+				)
+			},
+			true,
+		},
+		"different values same key": {
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("bar"), false,
+				)
+			},
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("baz"), false,
+				)
+			},
+			false,
+		},
+		"different sensitivity same value": {
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("bar"), false,
+				)
+			},
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("bar"), true,
+				)
+			},
+			false,
+		},
+		"different keys same count": {
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("val"), false,
+				)
+			},
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "bar"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("val"), false,
+				)
+			},
+			false,
+		},
+		"different count": {
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("val"), false,
+				)
+			},
+			func(ss *SyncState) {
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "foo"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("val"), false,
+				)
+				ss.SetOutputValue(
+					addrs.OutputValue{Name: "bar"}.Absolute(addrs.RootModuleInstance),
+					cty.StringVal("val2"), false,
+				)
+			},
+			false,
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			stateA := BuildState(test.SetupA)
+			stateB := BuildState(test.SetupB)
+			got := stateA.RootOutputValuesEqual(stateB)
+			if got != test.Want {
+				t.Errorf("wrong result for stateA.RootOutputValuesEqual(stateB)\ngot:  %t\nwant: %t", got, test.Want)
+			}
+		})
+	}
+}
+
 func TestState_MoveAbsResource(t *testing.T) {
 	// Set up a starter state for the embedded tests, which should start from a copy of this state.
 	state := NewState()