update: magpie update in a Homebrew install (brew install magpie, from the new tap in magpie-releases) says to brew upgrade magpie instead of replacing the binary in brew's Cellar, which would leave brew thinking the old version is there

internal/update/update.go

@@ -176,6 +176,13 @@ func Bundle() string {
 	return app
 }
 
+// Homebrew is whether exe was installed by Homebrew (brew install magpie),
+// which keeps it in its Cellar and has to be the one to upgrade it: a
+// binary replaced under it leaves brew thinking the old version is there.
+func Homebrew(exe string) bool {
+	return strings.Contains(filepath.ToSlash(exe), "/Cellar/magpie/")
+}
+
 // Executable is the running binary, symlinks resolved.
 func Executable() (string, error) {
 	exe, err := os.Executable()

internal/update/update_test.go

@@ -30,3 +30,16 @@ func TestReleased(t *testing.T) {
 		}
 	}
 }
+
+func TestHomebrew(t *testing.T) {
+	for exe, want := range map[string]bool{
+		"/opt/homebrew/Cellar/magpie/0.1.126/bin/magpie":              true,
+		"/home/linuxbrew/.linuxbrew/Cellar/magpie/0.1.126/bin/magpie": true,
+		"/usr/local/bin/magpie":                                       false,
+		"/Applications/magpie.app/Contents/MacOS/magpie":              false,
+	} {
+		if Homebrew(exe) != want {
+			t.Errorf("%s: %v", exe, !want)
+		}
+	}
+}

update_cli.go

@@ -51,6 +51,9 @@ func updateCmd(args []string) error {
 		fmt.Println(green.Render("✓"), "updated", tilde(app), "to", rel.Version, muted.Render("· quit and reopen magpie to use it"))
 		return nil
 	}
+	if exe, err := update.Executable(); err == nil && update.Homebrew(exe) {
+		return fmt.Errorf("this magpie was installed with Homebrew; update it with: brew upgrade magpie")
+	}
 	fmt.Println(muted.Render("  downloading " + update.BinaryAsset() + " …"))
 	if err := update.ReplaceBinary(ctx, rel); err != nil {
 		return err