Visual Studio 2026, OneAPI 2025.3.1 and "Step Into"

[DonRobinsonESSA]

I am using Visual Studio 2026 and Intel OneAPI HPC 2025.3.1 with OneAPI Fortran 2025.3.3 to compile and debug the Fortran parts of my VS26 solution. The solution (SLNX) is produced by Cmake 4.3.1. It builds and runs DLLs for code in C, C++ and Fortran, with Fortran being the largest component at over 500 subroutines. I'm happy with the build but have been having a multi-day struggle with the Visual Studio F11 key, which enables “step-into” debugging. An example of the failure message is:

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An error occurred while trying to open an editor.

Opening file 'C:\open-fvs-essadev\ESSAdev\metric\fire\vbase\fmpofl.f' in the source file editor failed. Operation not supported. Unknown error: 0x80070057. If this problem continues, try restarting Visual Studio, verify the editor for this source file language is installed and check if the source file is corrupt, for example if it has non-printable characters.

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All the solution’s projects (i.e. the DLLs) are compiled with debug information and no optimization. The F11 behaves correctly for portions of my code in C and C++, but fails for the Fortran.  In addition to migrating from VS22 to VS26 in search of a fix, I have tried to repair/modify both the VS26 and OneAPI installations as well as fully removing and a cleanly reinstalling (as far as I can tell) all the components. I have also followed many suggestions from Google Gemini; none of which has worked. In the Solution Explorer the file icons for the Fortran files (.f suffix) seem to be close to the icons for text-files, with a red down-arrow; while those for C and C++ look correct.

I am wondering if this is a known issue and what my options may be. I can work around not having F11 by placing a breakpoint in the called subroutine, but it is very handy to have it work directly.

[Steve_Lionel]

Thanks for providing the detail in your third paragraph - this hints at the problem (and solution). 

1. Close Visual Studio. Open the registry editor (regedit.exe).

2. Select Computer\HKEY_CLASSES_ROOT\.f90 and press Delete. Close regedit.

3. Run "Repair" on the Intel product that installed Fortran.

Let me know how this goes.

[DonRobinsonESSA]

Thanks for your suggestion Steve. I made the suggested registry key deletion followed by Modify > Repair, but it did not affect the F11 problem.

Two Q:

(1) I'm wondering if there would be any benefit to updating either the Fortran compiler from 2025.3.2 to 2025.3.3 or updating the entire toolkit from 2025.3.1 to 2026.0.0?

(2) Google Gemini had some suggestions about trying to add the .f suffix via the Solution Explorer "Open With..." for Fortran files. It also tacked along a similar vein to try to add a .f file via Debug > Options > Text Editor > File extensions, claiming that there should be a named editor for Intel Fortran. I found no such option. Your thoughts would be appreciated.

I'm getting used to the F11-F11 double-click going into and coming out of a "step-into" subroutine, so while it is not seamless, I can live with it. 

[DonRobinsonESSA · Accepted solution]

I updated OneAPI to 2026.0.0  (with the same 2026.0.0 Fortran compiler) and the problem continues at the "nice-to-have" level. I'm marking this as a solution and moving on.

I am curious about who (MS or Intel) would be the likely "fixer" of this? I guess I may never know.