DotNetExe FullPathOrDefaultis returning invalid path

[iskiselev]

Describe the bug

DotNetExe.FullPathOrDefault() should return full path or just dotnet. But TryFindDotNetExePath() always return some string (with fallback to "/usr/local/share/dotnet/dotnet" - which is invalid at least for Alpine).

Should it check if file exists anr return null if not - to allow FullPathOrDefault return just dotnet?

[natemcmaster]

@claude can you suggest a fix?

[claude]

Claude finished @natemcmaster's task in 1m 19s —— View job

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Fixing DotNetExe.FullPathOrDefault() returning invalid path

• Analyze the current code
• Implement fix with file existence check
• Run full build (build tools not permitted in this environment)
• Push changes (push permission denied)

Analysis

The bug is in TryFindDotNetExePath() in src/CommandLineUtils/Utilities/DotNetExe.cs:68. The method constructs a path from either DOTNET_ROOT env var or a hardcoded default (/usr/local/share/dotnet on Linux) and always returns it without checking if the file exists. This means FullPathOrDefault() never falls back to just "dotnet".

Suggested Fix

--- a/src/CommandLineUtils/Utilities/DotNetExe.cs
+++ b/src/CommandLineUtils/Utilities/DotNetExe.cs
@@ -65,7 +65,8 @@ namespace McMaster.Extensions.CommandLineUtils
                 dotnetRoot = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "C:\\Program Files\\dotnet" : "/usr/local/share/dotnet";
             }
 
-            return Path.Combine(dotnetRoot, fileName);
+            var dotnetPath = Path.Combine(dotnetRoot, fileName);
+            return File.Exists(dotnetPath) ? dotnetPath : null;
         }
     }
 }

Add a File.Exists check before returning the constructed path. When the file doesn't exist, return null so that FullPathOrDefault() correctly falls back to the plain "dotnet" name (which will be resolved via PATH at runtime).

This handles both cases:

• Default fallback path (/usr/local/share/dotnet/dotnet) doesn't exist (e.g., Alpine Linux) → returns null
• DOTNET_ROOT env var points to an invalid location → returns null

Note: I was unable to push this change due to permission restrictions. The fix is a one-line change if you'd like to apply it directly.

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[natemcmaster]

@claude can you make a pull request to fix this (and include test coverage?)

[claude]

Claude finished @natemcmaster's task in 2m 46s —— View job • claude/issue-600-20260405-0456 • Create PR ➔

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Fixing DotNetExe.FullPathOrDefault() returning invalid path

• Read current source code and tests
• Implement fix with File.Exists check
• Add test coverage
• Run full build (skipped — build tools not permitted, CI will validate)
• Push changes and create PR

Changes

src/CommandLineUtils/Utilities/DotNetExe.cs — Added File.Exists check in TryFindDotNetExePath(). When the constructed dotnet path doesn't exist (e.g., /usr/local/share/dotnet/dotnet on Alpine), the method now returns null so FullPathOrDefault() correctly falls back to "dotnet". Extracted FindDotNetInRoot as an internal method for testability.

test/CommandLineUtils.Tests/DotNetExeTests.cs — Added 4 new tests:

• FullPathOrDefaultReturnsPathOrDotnet — verifies the fallback contract
• FindDotNetInRoot_ReturnsNull_WhenDirectoryDoesNotExist — nonexistent directory
• FindDotNetInRoot_ReturnsNull_WhenFileDoesNotExist — existing directory, missing file
• FindDotNetInRoot_ReturnsPath_WhenFileExists — file exists at constructed path