Fix crash when PowerShell selection is changed (#2261)

* Fix crash when PowerShell selection is changed

* Change commented out dotnet global tool code

* Add tests

Author: rjmholt

src/platform.ts

@@ -116,11 +116,17 @@ export class PowerShellExeFinder {
      * @param configuredPowerShellPath the PowerShell path configured by the user.
      */
     public fixWindowsPowerShellPath(configuredPowerShellPath: string): string {
+        const altWinPS = this.findWinPS({ useAlternateBitness: true });
+
+        if (!altWinPS) {
+            return configuredPowerShellPath;
+        }
+
+        const lowerAltWinPSPath = altWinPS.exePath.toLocaleLowerCase();
         const lowerConfiguredPath = configuredPowerShellPath.toLocaleLowerCase();
-        const lowerAltWinPSPath = this.alternateBitnessWinPS.exePath.toLocaleLowerCase();
 
         if (lowerConfiguredPath === lowerAltWinPSPath) {
-            return this.winPS.exePath;
+            return this.findWinPS().exePath;
         }
 
         return configuredPowerShellPath;
@@ -180,7 +186,7 @@ export class PowerShellExeFinder {
         // Currently it cannot take startup arguments to start PSES with.
         //
         // Look for the .NET global tool
-        // yield this.pwshDotnetGlobalTool;
+        // yield this.findPSCoreDotnetGlobalTool();
 
         // Look for PSCore preview
         yield this.findPSCorePreview();

test/platform.test.ts

@@ -594,4 +594,47 @@ suite("Platform module", () => {
             });
         }
     });
+
+    suite("Windows PowerShell path fix", () => {
+        teardown(() => {
+            sinon.restore();
+            mockFS.restore();
+        });
+
+        for (const testPlatform of successTestCases
+                .filter((tp) => tp.platformDetails.operatingSystem === platform.OperatingSystem.Windows)) {
+
+            test(`Corrects the Windows PowerShell path on ${testPlatform.name}`, () => {
+                setupTestEnvironment(testPlatform);
+
+                function getWinPSPath(systemDir: string) {
+                    return path.join(
+                        testPlatform.environmentVars.windir,
+                        systemDir,
+                        "WindowsPowerShell",
+                        "v1.0",
+                        "powershell.exe");
+                }
+
+                const winPSPath = getWinPSPath("System32");
+
+                let altWinPSPath;
+                if (testPlatform.platformDetails.isProcess64Bit) {
+                    altWinPSPath = getWinPSPath("SysWOW64");
+                } else if (testPlatform.platformDetails.isOS64Bit) {
+                    altWinPSPath = getWinPSPath("Sysnative");
+                } else {
+                    altWinPSPath = null;
+                }
+
+                const powerShellExeFinder = new platform.PowerShellExeFinder(testPlatform.platformDetails);
+
+                assert.strictEqual(powerShellExeFinder.fixWindowsPowerShellPath(winPSPath), winPSPath);
+
+                if (altWinPSPath) {
+                    assert.strictEqual(powerShellExeFinder.fixWindowsPowerShellPath(altWinPSPath), winPSPath);
+                }
+            });
+        }
+    });
 });