fix incorrect use of loop variable (#16872)

This fixes a couple of references to loop variables in parallel tests
and deferred functions. When running a parallel test (calling
`t.Parallel()`) combined with the table-driven pattern, it's necessary
to copy the test case loop variable, otherwise only the last test case
is exercised. This is documented in the `testing` package:

https://pkg.go.dev/testing#hdr-Subtests_and_Sub_benchmarks

`defer` statements that invoke a closure should also not reference a
loop variable directly as the referenced value will change in each
iteration of the loop.

Issues were automatically found with the `loopvarcapture` linter.

changelog/16872.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+agent: fix incorrectly used loop variables in parallel tests and when finalizing seals
+```

command/agent/approle_end_to_end_test.go

@@ -54,6 +54,7 @@ func TestAppRoleEndToEnd(t *testing.T) {
 		if tc.removeSecretIDFile {
 			secretFileAction = "remove"
 		}
+		tc := tc // capture range variable
 		t.Run(fmt.Sprintf("%s_secret_id_file bindSecretID=%v secretIDLess=%v expectToken=%v", secretFileAction, tc.bindSecretID, tc.secretIDLess, tc.expectToken), func(t *testing.T) {
 			t.Parallel()
 			testAppRoleEndToEnd(t, tc.removeSecretIDFile, tc.bindSecretID, tc.secretIDLess, tc.expectToken)

command/kv_test.go

@@ -716,6 +716,7 @@ func TestKVPatchCommand_ArgValidation(t *testing.T) {
 	}
 
 	for _, tc := range cases {
+		tc := tc // capture range variable
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 

command/operator_diagnose.go

@@ -447,26 +447,25 @@ func (c *OperatorDiagnoseCommand) offlineDiagnostics(ctx context.Context) error
 		goto SEALFAIL
 	}
 
-	if seals != nil {
-		for _, seal := range seals {
-			// There is always one nil seal. We need to skip it so we don't start an empty Finalize-Seal-Shamir
-			// section.
-			if seal == nil {
-				continue
-			}
-			// Ensure that the seal finalizer is called, even if using verify-only
-			defer func(seal *vault.Seal) {
-				sealType := diagnose.CapitalizeFirstLetter((*seal).BarrierType().String())
-				finalizeSealContext, finalizeSealSpan := diagnose.StartSpan(ctx, "Finalize "+sealType+" Seal")
-				err = (*seal).Finalize(finalizeSealContext)
-				if err != nil {
-					diagnose.Fail(finalizeSealContext, "Error finalizing seal.")
-					diagnose.Advise(finalizeSealContext, "This likely means that the barrier is still in use; therefore, finalizing the seal timed out.")
-					finalizeSealSpan.End()
-				}
+	for _, seal := range seals {
+		// There is always one nil seal. We need to skip it so we don't start an empty Finalize-Seal-Shamir
+		// section.
+		if seal == nil {
+			continue
+		}
+		seal := seal // capture range variable
+		// Ensure that the seal finalizer is called, even if using verify-only
+		defer func(seal *vault.Seal) {
+			sealType := diagnose.CapitalizeFirstLetter((*seal).BarrierType().String())
+			finalizeSealContext, finalizeSealSpan := diagnose.StartSpan(ctx, "Finalize "+sealType+" Seal")
+			err = (*seal).Finalize(finalizeSealContext)
+			if err != nil {
+				diagnose.Fail(finalizeSealContext, "Error finalizing seal.")
+				diagnose.Advise(finalizeSealContext, "This likely means that the barrier is still in use; therefore, finalizing the seal timed out.")
 				finalizeSealSpan.End()
-			}(&seal)
-		}
+			}
+			finalizeSealSpan.End()
+		}(&seal)
 	}
 
 	if barrierSeal == nil {

command/server.go

@@ -1337,16 +1337,20 @@ func (c *ServerCommand) Run(args []string) int {
 		return 1
 	}
 
-	if seals != nil {
-		for _, seal := range seals {
-			// Ensure that the seal finalizer is called, even if using verify-only
-			defer func(seal *vault.Seal) {
-				err = (*seal).Finalize(context.Background())
-				if err != nil {
-					c.UI.Error(fmt.Sprintf("Error finalizing seals: %v", err))
-				}
-			}(&seal)
+	for _, seal := range seals {
+		// There is always one nil seal. We need to skip it so we don't start an empty Finalize-Seal-Shamir
+		// section.
+		if seal == nil {
+			continue
 		}
+		seal := seal // capture range variable
+		// Ensure that the seal finalizer is called, even if using verify-only
+		defer func(seal *vault.Seal) {
+			err = (*seal).Finalize(context.Background())
+			if err != nil {
+				c.UI.Error(fmt.Sprintf("Error finalizing seals: %v", err))
+			}
+		}(&seal)
 	}
 
 	if barrierSeal == nil {