How to fix MethodError - undefined method `real_path` with CocoaPods

NoMethodError - undefined method {% raw %}`real_path' for nil:NilClass
```
I then tried running `pod deintegrate` to start from scratch, but that command fails as well.

My next try is with `cocoapods 1.6.0` and `cocoapods 1.6.1` but the problem still persists.

`undefined method` in Ruby means that we are calling a method on an object that is nil. I like to track down problems via reading code, but this error is very vague.

Looking thorough at the log, I see CocoaPods has done fetching dependencies, but fails at the integration step, so it must be something wrong with my project file.

Then I trace back commits to `project.pbxproj` to see if there's anything wrong. It turns out that there was a commit that accidentally removes `Pods-MyApp Staging.release.xcconfig` from project. That also comes with removal of

```
baseConfigurationReference = B7FC69316CC27F11022F8A82 /* Pods-MyApp Staging.release.xcconfig */;
```
## CocoaPods uses xcconfig
As you know, CocoaPods uses `xcconfig` files to declare pod related information like `FRAMEWORK_SEARCH_PATHS`, `OTHER_LDFLAGS` and other variables like

```
PODS_BUILD_DIR = ${BUILD_DIR}
PODS_CONFIGURATION_BUILD_DIR = ${PODS_BUILD_DIR}/$(CONFIGURATION)$(EFFECTIVE_PLATFORM_NAME)
PODS_PODFILE_DIR_PATH = ${SRCROOT}/.
PODS_ROOT = ${SRCROOT}/Pods
```
And for a normal `pod install`, CocoaPods adds some `xcconfig` files to your project, and the path is `Pods/Target Support Files/Pods-DeepDiffDemo`. There will always be `debug.xcconfig` and `release.xcconfig` for each of your project target.

<img alt="xcconfig" width="1678" src="https://user-images.githubusercontent.com/2284279/53345363-0dcac600-3915-11e9-975f-e6a7207912d0.png">

If your project MyApp has a production target called `MyApp Production` and `MyApp Staging`, then you should have these files

```
Pods-MyApp Staging.debug.xcconfig
Pods-MyApp Staging.release.xcconfig
Pods-MyApp Production.debug.xcconfig
Pods-MyApp Production.release.xcconfig
```
These are added to projects but not checked to any targets. Just like plist, you don't need to add xcconfig files to target.

If you go to project Info page, you will see that these xcconfig files are selected

<img alt="project" width="824" src="https://user-images.githubusercontent.com/2284279/53345592-93e70c80-3915-11e9-9826-3d1b9f30b900.png">

## Missing xcconfig
In my case, `Pods-MyApp Staging.release.xcconfig` was somehow missing from project, hence all pod commands fail.

The fix is to re-add that file and select that xcconfig in project Info page

Original post https://github.com/onmyway133/blog/issues/170