Check dotnet path without which or where first (#2234)

* Check dotnet without which or where first

Which and where can be slow to find. For the common case which we want to make fast, we can just check 'dotnet' first and see if that works.

Note: Ideally, this function would only return a string, but that would require writing a wrapper around this return type just for this function and does not follow the other existing patterns.

With respect to tests: This should be covered by the existing 'find path' tests.

* Utilize a finally block

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: nagilson

vscode-dotnet-runtime-extension/src/extension.ts

@@ -515,6 +515,17 @@ export function activate(vsCodeContext: vscode.ExtensionContext, extensionContex
         const validator = new DotnetConditionValidator(workerContext, utilContext);
         const finder = new DotnetPathFinder(workerContext, utilContext);
 
+        const dotnetOnShellSpawn = (await finder.findDotnetFastFromListOnly())?.[0] ?? '';
+        if (dotnetOnShellSpawn)
+        {
+            const validatedShellSpawn = await getPathIfValid(dotnetOnShellSpawn, validator, commandContext);
+            if (validatedShellSpawn)
+            {
+                loggingObserver.dispose();
+                return { dotnetPath: validatedShellSpawn };
+            }
+        }
+
         const dotnetsOnPATH = await finder.findRawPathEnvironmentSetting();
         for (const dotnetPath of dotnetsOnPATH ?? [])
         {

vscode-dotnet-runtime-library/src/Acquisition/DotnetPathFinder.ts

@@ -92,6 +92,23 @@ export class DotnetPathFinder implements IDotnetPathFinder
         return undefined;
     }
 
+    /**
+     * @remarks This only checks dotnet --list-runtimes or --list-sdks, so it can be more performant for the base case.
+     * This allows skipping which, where, and also does not rely on --info which is slower because it shells to the SDK instead of just being the host.
+     * @returns The path to the dotnet executable, which may be a symlink to the actual executable.
+     */
+    public async findDotnetFastFromListOnly(): Promise<string[] | undefined>
+    {
+        const oldLookup = process.env.DOTNET_MULTILEVEL_LOOKUP;
+        try {
+            process.env.DOTNET_MULTILEVEL_LOOKUP = '0'; // make it so --list-runtimes only finds the runtimes on that path: https://learn.microsoft.com/en-us/dotnet/core/compatibility/deployment/7.0/multilevel-lookup#reason-for-change
+            const finalPath = await this.getTruePath(['dotnet']);
+            return this.returnWithRestoringEnvironment(finalPath, 'DOTNET_MULTILEVEL_LOOKUP', oldLookup);
+        } finally {
+            process.env.DOTNET_MULTILEVEL_LOOKUP = oldLookup; // Ensure the environment variable is always restored
+        }
+    }
+
     /**
      *
      * @returns A set of the path environment variable(s) for which or where dotnet, which may need to be converted to the actual path if it points to a polymorphic executable.