IntelliJ not recognizing a particular file correctly, instead it's stuck as a text file

Question

Please ensure that this file (or a pattern that represents it) is not listed under

Settings → Editor → File Types→ Text

For OS X

Preferences → Editor → File Types→ Text

Sometimes the file or pattern are stuck under File type auto-detected by file content instead of Text.

Step 1: Click "File" ==> "Settings" for Windows or "InterlliJ IDEA" ==> "Preferences" for Mac

Step 2: Expand "Editor" & Click "File Types"

Step 3: You will see all file types on Right. Navigate to the "Text" entry and click it

Step 4: You should able to see your file name on the bottom of "Registered Patterns" (lower box)

Step 5: Remove your file from the "Registered Patterns". The problem should be solved and let you rename with fileName.java

Step 6: If not, delete the file from the project and create it again with name fileName

Source

In 2020 none of the posted answers worked, here's what did:

1. Left click the file
2. On the top toolbar, select File -> File Properties -> Associate with File Type

OSX:

Preferences > Editor > File Types > Text

Windows:

Settings > Editor > File Types > Text Files

I had the same problem and none of the above solution solved it. The thing that at the end solved it was by selecting the module and going to the module settings(press F4 on the module name)

Then in the Sources tab, select the "java" folder and press on the Sources button. That tells IntelliJ that the folder in question is a source code folder.

Then select the Test folder and press Tests.

That's it. Then it will recognize correctly the files and show errors as needed.

See below the screenshot.

I solved the same issue by

Right-click on the file ->  "Override File Type" -> Select the extension type the file has.