fix: use specific config file for loading (#2573) (#2580)

Ensures that Viper loads the specific configuration file provided via the
--config-file flag by using SetConfigFile instead of SetConfigName and
AddConfigPath. This prevents filename ambiguity when multiple files with
the same base name but different extensions exist in the same directory.

Similar to AlloyDB Auth Proxy PR #914.

Author: kgala2

cmd/config_test.go

@@ -82,7 +82,7 @@ func TestNewCommandWithConfigFile(t *testing.T) {
 		},
 		{
 			desc: "instance env overrides config file precedence",
-			args: []string{"--config-file", "testdata/config.json"},
+			args: []string{"--config-file", "testdata/config-json.json"},
 			setup: func() {
 				t.Setenv("CSQL_PROXY_INSTANCE_CONNECTION_NAME", "p:r:i")
 			},
@@ -104,7 +104,7 @@ func TestNewCommandWithConfigFile(t *testing.T) {
 			desc: "flag overrides config file precedence",
 			args: []string{
 				"proj:region:inst",
-				"--config-file", "testdata/config.toml",
+				"--config-file", "testdata/config-toml.toml",
 				"--debug",
 			},
 			setup: func() {},
@@ -116,7 +116,7 @@ func TestNewCommandWithConfigFile(t *testing.T) {
 			desc: "env overrides config file precedence",
 			args: []string{
 				"proj:region:inst",
-				"--config-file", "testdata/config.toml",
+				"--config-file", "testdata/config-toml.toml",
 			},
 			setup: func() {
 				t.Setenv("CSQL_PROXY_DEBUG", "false")
@@ -125,6 +125,20 @@ func TestNewCommandWithConfigFile(t *testing.T) {
 				assert(t, false, c.conf.Debug)
 			},
 		},
+		{
+			desc: "specific config file extension prioritization",
+			args: []string{
+				"proj:region:inst",
+				"--config-file", "testdata/priority.toml",
+			},
+			setup: func() {},
+			assert: func(t *testing.T, c *Command) {
+				// priority.toml has max-connections = 5555 and port = 5555
+				// priority.json has max-connections = 6666 and port = 6666
+				assert(t, uint64(5555), c.conf.MaxConnections)
+				assert(t, 5555, c.conf.Port)
+			},
+		},
 	}
 
 	for _, tc := range tcs {

cmd/root.go

@@ -666,10 +666,6 @@ func initViper(c *Command) (*viper.Viper, error) {
 	v := viper.New()
 
 	if c.conf.Filepath != "" {
-		// Setup Viper configuration file. Viper will attempt to load
-		// configuration from the specified file if it exists. Otherwise, Viper
-		// will source all configuration from flags and then environment
-		// variables.
 		ext := filepath.Ext(c.conf.Filepath)
 
 		badExtErr := newBadCommandError(
@@ -685,11 +681,7 @@ func initViper(c *Command) (*viper.Viper, error) {
 			return nil, badExtErr
 		}
 
-		conf := filepath.Base(c.conf.Filepath)
-		noExt := strings.ReplaceAll(conf, ext, "")
-		// argument must be the name of config file without extension
-		v.SetConfigName(noExt)
-		v.AddConfigPath(filepath.Dir(c.conf.Filepath))
+		v.SetConfigFile(c.conf.Filepath)
 
 		// Attempt to load configuration from a file. If no file is found,
 		// assume configuration is provided by flags or environment variables.

cmd/testdata/priority.json

@@ -0,0 +1,4 @@
+{
+  "max-connections": 6666,
+  "port": 6666
+}

cmd/testdata/priority.toml

@@ -0,0 +1,2 @@
+max-connections = 5555
+port = 5555