Stop startup on a list or map setting in neoirc.yaml (closes #268)

Every setting is now read through one helper that uses cast.ToStringE,
the conversion viper.GetString wraps, keeping its error instead of
returning the empty string. TRUSTED_PROXIES uses the same helper. A
config file that does not parse makes New return an error naming the
file instead of panicking.

Model: opus-5-5

internal/config/config_test.go

@@ -287,49 +287,93 @@ func TestTrustedProxies(t *testing.T) {
 	}
 }
 
-func TestTrustedProxiesNotAStringInYAMLStopsStartup(t *testing.T) {
-	// YAML reads the first value as a list and the second as a map.
-	values := []string{"[10.0.0.1]", "{proxy: 10.0.0.1}"}
+// unsetEnv removes the environment variable key for the rest of the
+// test, so that config.New reads key from the config file.
+func unsetEnv(t *testing.T, key string) {
+	t.Helper()
 
-	for _, value := range values {
-		t.Run(value, func(t *testing.T) {
-			// t.Setenv puts back whatever value was there after the
-			// test, including when Unsetenv removes it.
-			t.Setenv("TRUSTED_PROXIES", "")
+	// t.Setenv puts back whatever value was there after the test,
+	// including when Unsetenv removes it.
+	t.Setenv(key, "")
 
-			err := os.Unsetenv("TRUSTED_PROXIES")
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			// loadConfig names the app neoirc-test, so config.New reads
-			// $HOME/.config/neoirc-test/neoirc-test.yaml.
-			home := t.TempDir()
-			t.Setenv("HOME", home)
-
-			dir := filepath.Join(home, ".config", "neoirc-test")
-
-			err = os.MkdirAll(dir, 0o700)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			err = os.WriteFile(
-				filepath.Join(dir, "neoirc-test.yaml"),
-				[]byte("TRUSTED_PROXIES: "+value+"\n"), 0o600,
-			)
-			if err != nil {
-				t.Fatal(err)
-			}
-
-			// Viper keeps the values it read from this file after the
-			// file is gone. Reset clears them for later tests.
-			t.Cleanup(viper.Reset)
-
-			_, err = loadConfig(t)
-			if err == nil || !strings.Contains(err.Error(), "TRUSTED_PROXIES") {
-				t.Errorf("error = %v, want one naming TRUSTED_PROXIES", err)
-			}
-		})
+	err := os.Unsetenv(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+// writeConfigFile writes content to the config file config.New reads
+// when HOME is home, and returns the file's path.
+func writeConfigFile(t *testing.T, home, content string) string {
+	t.Helper()
+
+	// loadConfig names the app neoirc-test, so config.New reads
+	// $HOME/.config/neoirc-test/neoirc-test.yaml.
+	dir := filepath.Join(home, ".config", "neoirc-test")
+
+	err := os.MkdirAll(dir, 0o700)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	path := filepath.Join(dir, "neoirc-test.yaml")
+
+	err = os.WriteFile(path, []byte(content), 0o600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Viper keeps the file and the values it read from it after the
+	// file is gone. Reset clears them for later tests.
+	t.Cleanup(viper.Reset)
+
+	return path
+}
+
+func TestListOrMapInConfigFileStopsStartup(t *testing.T) {
+	// YAML reads the first value as a list and the second as a map.
+	values := []string{`[":6667"]`, `{addr: ":6667"}`}
+	keys := []string{"IRC_LISTEN_ADDR", "MOTD", "TRUSTED_PROXIES"}
+
+	for _, key := range keys {
+		for _, value := range values {
+			t.Run(key+"="+value, func(t *testing.T) {
+				home := t.TempDir()
+				t.Setenv("HOME", home)
+				unsetEnv(t, key)
+				writeConfigFile(t, home, key+": "+value+"\n")
+
+				_, err := loadConfig(t)
+				if err == nil || !strings.Contains(err.Error(), key) {
+					t.Errorf("error = %v, want one naming %s", err, key)
+				}
+			})
+		}
+	}
+}
+
+func TestSingleValuesInConfigFileAreUsed(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	unsetEnv(t, "PORT")
+	unsetEnv(t, "DEBUG")
+	unsetEnv(t, "MOTD")
+	writeConfigFile(t, home, "PORT: 9000\nDEBUG: true\nMOTD: hello\n")
+
+	cfg := newConfig(t)
+	if cfg.Port != 9000 || !cfg.Debug || cfg.MOTD != "hello" {
+		t.Errorf("Port, Debug, MOTD = %d, %t, %q, want 9000, true, %q",
+			cfg.Port, cfg.Debug, cfg.MOTD, "hello")
+	}
+}
+
+func TestConfigFileThatDoesNotParseStopsStartup(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	path := writeConfigFile(t, home, "MOTD: [unclosed\n")
+
+	_, err := loadConfig(t)
+	if err == nil || !strings.Contains(err.Error(), path) {
+		t.Errorf("error = %v, want one naming %s", err, path)
 	}
 }