ReadConfig(in io.Reader) does not Actually ReadConfig

[dp1140a]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.
• I am not looking for support or already pursued the available support channels without success.
• I have checked the troubleshooting guide for my problem, without success.

Viper Version

1.18.2

Go Version

1.22

Config Source

Files

Format

TOML

Repl.it link

No response

Code reproducing the issue

/**
testdata/good_config.toml is a good toml file.
Viper sees it initially
**/
f, err := os.Open("testdata/good_config.toml")
if err != nil {
   assert.Fail(suite.T(), err.Error())
}
err = viper.ReadConfig(f)
if err != nil {
  assert.Fail(suite.T(), err.Error())
}

Expected Behavior

should read the config. When I print the config I expect the contents of the initial file. but I get {}

Actual Behavior

Return an empty config

Steps To Reproduce

No response

Additional Information

Did some initial debugging on this.

At this point all is well.

Here is where things start to hinky

Still dont have a file tto read? Ok says Viper Ill try to find the config file . . . But wait!

Here you can see that configPath has never been set. It still has not set the configFile or pconfigPath despite asking for a file reader that has the name and path of the file. The reult is that it cant find the config file and fails.

BUT!!!
This code works:

file := "testdata/good_config.toml"
viper.SetConfigName(strings.TrimSuffix(filepath.Base(file), filepath.Ext(file)))
viper.SetConfigType("toml")
viper.AddConfigPath(filepath.Dir(file))
f, err := os.Open(file)
if err != nil {
   assert.Fail(suite.T(), err.Error())
}
err = viper.ReadConfig(f)
if err != nil {
  assert.Fail(suite.T(), err.Error())
}

So why would I go through all that trouble to use ReadConfig(f) when I could just go through the same trouble and use ReadInConfig()?

Seems like ReadConfig(f) should just ReadConfig from f

[github-actions]

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[mazenharake]

This seems to come up as a consequence of not specifying the config type. If you read in a file it still needs to be interpreted in some way and since the config type has not been set then getConfigType() resorts to trying to find the file instead and inferring the config type from the file extension. This is (probably) why your working example is successful.

See https://github.com/spf13/viper/blob/master/viper.go#L2218

I'll admit it is quirky behavior... perhaps adding a default case here https://github.com/spf13/viper/blob/master/viper.go#L1804 and retur an error would be more suitable since the function assumes that a config type has been set either explicitly using SetConfigType or by using SetConfigFile()+ReadInConfig()

Either way, using SetConfigType should resolve this issue?

[sagikazarmark]

I believe @mazenharake is correct.