‘Differs only in casing’ class of problems

Error message from TypeScript compiler

This one attacked me yesterday by the end of the day. This is a TypeScript project with some instrumentation done with gulp. The command shown attempts to launch TypeScript compiler. The console is standard git bash for Windows. I didn’t realize what was going on there at the first sight. The messages were confusing and mysterious. I made sure I didn’t have any changes in the repository comparing to the HEAD. I opened the folder in Visual Studio Code and everything was fine. It was only the compiler which saw the problems.

The next day I figured out there is a small detail in my path. Just take a look at directory names casing:

TypeScript compiler ran successfully

After changing the directory using names with proper casing everything was fine. What actually happened was that, I somehow opened the git bash providing the current directory name using lower case letters. It is not that difficult to do that. This is a flaw in the MINGW implementation of bash, I think. It just allows you to change the directory using its name written with whatever case. That is not the problem itself, because cmd.exe allows you to do so as well. The problem is that it then stores the path (probably in PWD environment variable). Some cross-platform tools, which are case sensitive on other platforms, when executed from git bash with mismatched working directory casing may begin to treat such path as separate one, different from the original one. Especially tools which process files using their paths relative to the current directory, like TypeScript compiler for instance.

This can possibly be a wider class of problems and I guess there are other development tools which behave like that when launched from git bash under before mentioned conditions.

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