Ignore --scratch-path when calling swift package plugin --list

If the user has a `swift.buildPath` set, and they've got
backgroundCompilation turned on, the extension will attempt to list
their package's plugins with a `--scratch-path`, which `swift package
plugin --list` does not accept. This causes the command to fail.

Omit this argument from the command.

Author: plemarquand

src/extension.ts

@@ -222,10 +222,9 @@ function handleFolderEvent(logger: SwiftLogger): (event: FolderEvent) => Promise
     // function called when a folder is added. I broke this out so we can trigger it
     // without having to await for it.
     async function folderAdded(folder: FolderContext, workspace: WorkspaceContext) {
-        if (
-            !configuration.folder(folder.workspaceFolder).disableAutoResolve ||
-            configuration.backgroundCompilation.enabled
-        ) {
+        const disableAutoResolve = configuration.folder(folder.workspaceFolder).disableAutoResolve;
+        const backgroundCompilationEnabled = configuration.backgroundCompilation.enabled;
+        if (!disableAutoResolve || backgroundCompilationEnabled) {
             // if background compilation is set then run compile at startup unless
             // this folder is a sub-folder of the workspace folder. This is to avoid
             // kicking off compile for multiple projects at the same time

src/toolchain/BuildFlags.ts

@@ -44,20 +44,27 @@ export class BuildFlags {
     private withSwiftSDKFlags(args: string[]): string[] {
         switch (args[0]) {
             case "package": {
-                const subcommand = args.splice(0, 2).concat(this.buildPathFlags());
-                switch (subcommand[1]) {
-                    case "dump-symbol-graph":
-                    case "diagnose-api-breaking-changes":
-                    case "resolve": {
-                        // These two tools require building the package, so SDK
-                        // flags are needed. Destination control flags are
-                        // required to be placed before subcommand options.
-                        return [...subcommand, ...this.swiftpmSDKFlags(), ...args];
+                switch (args[1]) {
+                    case "plugin":
+                        // Don't append build path flags for `swift package plugin` commands
+                        return args;
+                    default: {
+                        const subcommand = args.splice(0, 2).concat(this.buildPathFlags());
+                        switch (subcommand[1]) {
+                            case "dump-symbol-graph":
+                            case "diagnose-api-breaking-changes":
+                            case "resolve": {
+                                // These two tools require building the package, so SDK
+                                // flags are needed. Destination control flags are
+                                // required to be placed before subcommand options.
+                                return [...subcommand, ...this.swiftpmSDKFlags(), ...args];
+                            }
+                            default:
+                                // Other swift-package subcommands operate on the host,
+                                // so it doesn't need to know about the destination.
+                                return subcommand.concat(args);
+                        }
                     }
-                    default:
-                        // Other swift-package subcommands operate on the host,
-                        // so it doesn't need to know about the destination.
-                        return subcommand.concat(args);
                 }
             }
             case "build":
@@ -212,6 +219,9 @@ export class BuildFlags {
         const disableSandboxFlags = ["--disable-sandbox", "-Xswiftc", "-disable-sandbox"];
         switch (args[0]) {
             case "package": {
+                if (args[1] === "plugin") {
+                    return args;
+                }
                 return [args[0], ...disableSandboxFlags, ...args.slice(1)];
             }
             case "build":

test/unit-tests/toolchain/BuildFlags.test.ts

@@ -12,6 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import { expect } from "chai";
+import { beforeEach } from "mocha";
 import * as sinon from "sinon";
 
 import configuration from "@src/configuration";
@@ -242,6 +243,13 @@ suite("BuildFlags Test Suite", () => {
 
     suite("withAdditionalFlags", () => {
         const sdkConfig = mockGlobalValue(configuration, "sdk");
+        const buildPathConfig = mockGlobalValue(configuration, "buildPath");
+
+        beforeEach(() => {
+            buildPathConfig.setValue("");
+            sdkConfig.setValue("");
+            sandboxConfig.setValue(false);
+        });
 
         test("package", () => {
             for (const sub of ["dump-symbol-graph", "diagnose-api-breaking-changes", "resolve"]) {
@@ -284,6 +292,29 @@ suite("BuildFlags Test Suite", () => {
             ]);
         });
 
+        test("package plugin", () => {
+            buildPathConfig.setValue("");
+            sdkConfig.setValue("");
+            expect(
+                buildFlags.withAdditionalFlags(["package", "plugin", "my-plugin"])
+            ).to.deep.equal(["package", "plugin", "my-plugin"]);
+
+            buildPathConfig.setValue("/some/build/path");
+            expect(
+                buildFlags.withAdditionalFlags(["package", "plugin", "my-plugin", "--verbose"])
+            ).to.deep.equal(["package", "plugin", "my-plugin", "--verbose"]);
+
+            sdkConfig.setValue("/some/full/path/to/sdk");
+            expect(
+                buildFlags.withAdditionalFlags(["package", "plugin", "my-plugin"])
+            ).to.deep.equal(["package", "plugin", "my-plugin"]);
+
+            sandboxConfig.setValue(true);
+            expect(
+                buildFlags.withAdditionalFlags(["package", "plugin", "my-plugin"])
+            ).to.deep.equal(["package", "plugin", "my-plugin"]);
+        });
+
         test("build", () => {
             sdkConfig.setValue("");
             expect(