qmake cannot run g++: $$system() not working under Windows 7

[Ashpool]

I've been struggling with this issue for two days now.
I am trying to compile a very simple project with QTCreator using the MinGW 5.3.0 kit under Windows 7, but I get the following error from qmake:

Project ERROR: Cannot run compiler 'g++'. Output:
===================
===================
Maybe you forgot to setup the environment?

I double-checked that the compiler was in place and functional. Investigating the issue further, I found out that the error occurs when parsing the mingw53_32/mkspecs/features/toolchain.prf file on this line:

output = $$system("$$cmd_prefix $$QMAKE_CXX $$qtMakeExpand($$cxx_flags) -xc++ - 2>&1 $$cmd_suffix", lines, ec)

which expands to

output = $$system("set LC_ALL=C& g++ -fno-keep-inline-dllexport -E -v -xc++ - 2>&1 <NUL >NUL", lines, ec)

Turns out, the $$system() function does not output anything at all no matter the arguments. For example, I tried substituting it with

output =  $$system("echo test")

and still the contents of output were empty. I know this because I tried launching qmake manually with the -d flag. I also played around with the toolchain.prf file a little, adding some debug output. Here i attached the log file I got from this command:

D:\Qt\5.11.3\mingw53_32\bin>D:\Qt\5.11.3\mingw53_32\bin\qmake.exe D:\QTProjects\untitled9\untitled9.pro -spec win32-g++ "CONFIG+=debug" "CONFIG+=qml_debug" -d > qmake-test.txt 2>&1

This is happening with Qt 5.11.3., but it is also relevant to 5.12.2 and 5.13.0. In fact, I downgraded from those in hopes of curing this problem. I'm glad to share any additional info that is required to resolve this issue. Please help, it's driving me crazy.

[SGaist]

Hi and welcome to devnet,

Might be a silly question but did you install MinGW through the Qt installer also ?

[Ashpool]

@SGaist yes, I did. I also tried using a manually added compiler from the MSYS2 package installed separately, with the same result

[SGaist]

Do you have any yellow/red icon in your kit page in Qt Creator's preferences ?

[Ashpool]

@SGaist no, the kit appears to have been configured properly. The bundled gcc, g++ and gdb were nicely detected out-of-the-box.

[SGaist]

Did you try to close Qt Creator, nuke the build folder, the .pro.user file and then reconfigure your project ?

[Ashpool]

@SGaist no, but I did create new helloworld projects several times. Also, as far as I can tell, the problem occurs before any project-specific files and settings get involved

[SGaist]

Do you still currently have several versions of MinGW ?

If so, can you remove the others ?

[Ashpool]

@SGaist I will try that as soon as I get to my workstation. However what I did try was nuking the QTCreator's folder in AppData/Roaming, which caused all settings to reset, which included forgetting those manually added MinGW compilers. The bundled ones were detected again, and the kits were shown as if configured correctly

[Ashpool]

@SGaist I removed all versions of MinGW except the one that came with Qt. My kit page in Qt Creator's preferences now has only one auto-detected kit "Desktop Qt 5.11.3 MinGW 32bit" which shows no errors or warnings. It's configured to use the MinGW binaries from Qt\Tools\mingw530_32\bin\. Upon creating a new Qt Widgets project the issue persists. There's also this message before I even try to build the project:

Project ERROR: failed to parse default search paths from compiler output

and any Qt-related symbols and includes in the code editor are highlighted as unknown. It was there all along, I just didn't mention it. I believe it is caused by the same issue I described in the original post.

I should also mention that I did not compile Qt manually or make any modifications to it. I used the default online installer to install 5.12.2 and 5.13.0, and I used an offline installer to install 5.11.3.

[Ashpool]

I used the ProcessMonitor application from the Windows SysInternals Suite to try to determine where things go wrong. It looks like qmake.exe doesn't even try to run g++. If it did, — unsuccessfully — the log would contain a line which would look like
qmake.exe — QueryOpen — D:\some\path\which\doesnt\exist\g++.exe — NAME NOT FOUND
This, as you can see from the screenshot, is not the case.

[Ashpool]

This is how my kits and compilers pages in preferences are looking currently. Sorry for the Russian captions.

Kits:

Compilers:

[SGaist]

All looks pretty good...

I suppose you can also successfully start g++ from the command line if you use the full path to the compiler ?

[Ashpool]

@SGaist yes, indeed I can. I also added D:\Qt\Tools\mingw530_32\bin, the path containing it, to the PATH environment variable, just for good measure.

[SGaist]

I am currently running out of ideas...

As a last resort, did you try a full Qt uninstallation/computer reboot/Qt installation ?