fix: respect --server-side flag in helm upgrade --install

Fixes #31627

When using helm upgrade --install on a non-existent release, the
--server-side flag was not being respected. This was because the
upgrade client uses ServerSideApply as a string ("true", "false", "auto")
while the install client uses it as a boolean, and the conversion
was missing when creating the install client.

This fix adds proper conversion logic to ensure that:
- --server-side=true -> install with server-side apply
- --server-side=false -> install with client-side apply
- --server-side=auto or unset -> default to server-side apply

Also adds TestUpgradeInstallServerSideApply to verify the fix works correctly.
The test has been enhanced to actually verify the ApplyMethod field on releases
to ensure the --server-side flag is properly passed through.

Signed-off-by: Azeez Syed <syedazeez337@gmail.com>

pkg/cmd/upgrade.go

@@ -154,6 +154,17 @@ func newUpgradeCmd(cfg *action.Configuration, out io.Writer) *cobra.Command {
 					instClient.HideSecret = client.HideSecret
 					instClient.TakeOwnership = client.TakeOwnership
 
+					// Convert ServerSideApply from string (upgrade) to bool (install)
+					switch client.ServerSideApply {
+					case "true":
+						instClient.ServerSideApply = true
+					case "false":
+						instClient.ServerSideApply = false
+					case "auto", "":
+						// For "auto" or empty, default to true (server-side apply)
+						instClient.ServerSideApply = true
+					}
+
 					if isReleaseUninstalled(versions) {
 						instClient.Replace = true
 					}

pkg/cmd/upgrade_test.go

@@ -605,3 +605,53 @@ func TestUpgradeWithDryRun(t *testing.T) {
 		t.Error("expected error when --hide-secret used without --dry-run")
 	}
 }
+
+func TestUpgradeInstallServerSideApply(t *testing.T) {
+	releaseName := "test-server-side-apply"
+	chartPath := "testdata/testcharts/chart-with-subchart-notes"
+	
+	store := storageFixture()
+	
+	// Test that --server-side=false is properly passed to install client
+	cmd := fmt.Sprintf("upgrade %s -i --server-side=false '%s'", releaseName, chartPath)
+	_, _, err := executeActionCommandC(store, cmd)
+	if err != nil {
+		t.Errorf("unexpected error with --server-side=false: %v", err)
+	}
+	
+	// Verify the release was created and check ApplyMethod
+	reli, err := store.Get(releaseName, 1)
+	if err != nil {
+		t.Errorf("failed to get release: %v", err)
+	}
+	rel, err := releaserToV1Release(reli)
+	if err != nil {
+		t.Errorf("failed to convert release to *release.Release: %v", err)
+	}
+	// Check that ApplyMethod is not "ssa" (should be client-side apply)
+	if rel.ApplyMethod == "ssa" {
+		t.Errorf("expected release to use client-side apply, but ApplyMethod is 'ssa'")
+	}
+	
+	// Test that --server-side=true is properly passed to install client
+	releaseName2 := "test-server-side-apply-true"
+	cmd = fmt.Sprintf("upgrade %s -i --server-side=true '%s'", releaseName2, chartPath)
+	_, _, err = executeActionCommandC(store, cmd)
+	if err != nil {
+		t.Errorf("unexpected error with --server-side=true: %v", err)
+	}
+	
+	// Verify the release was created and check ApplyMethod
+	reli2, err := store.Get(releaseName2, 1)
+	if err != nil {
+		t.Errorf("failed to get release: %v", err)
+	}
+	rel2, err := releaserToV1Release(reli2)
+	if err != nil {
+		t.Errorf("failed to convert release to *release.Release: %v", err)
+	}
+	// Check that ApplyMethod is "ssa" (server-side apply)
+	if rel2.ApplyMethod != "ssa" {
+		t.Errorf("expected release to use server-side apply, but ApplyMethod is '%s'", rel2.ApplyMethod)
+	}
+}