src/goLanguageServer: fix missing gopls detection logic

Also, update getMissingTools to check the tool's existence
by simply checking whether the resolved tool path is absolute.
getBinPath already ran the existence check before returning
the absolute path for the tool.

Fixes #3194

src/goInstallTools.ts

@@ -346,6 +346,7 @@ export async function promptForMissingTool(toolName: string) {
 	const installOptions = ['Install'];
 	let missing = await getMissingTools(goVersion);
 	if (!containsTool(missing, tool)) {
+		console.log(`not containsTool ${missing}, ${tool}, ${goVersion}`);
 		return;
 	}
 	missing = missing.filter((x) => x === tool || tool.isImportant);
@@ -544,9 +545,7 @@ function getMissingTools(goVersion: GoVersion): Promise<Tool[]> {
 			(tool) =>
 				new Promise<Tool>((resolve, reject) => {
 					const toolPath = getBinPath(tool.name);
-					fs.exists(toolPath, (exists) => {
-						resolve(exists ? null : tool);
-					});
+					resolve(path.isAbsolute(toolPath) ? null : tool);
 				})
 		)
 	).then((res) => {

src/goLanguageServer.ts

@@ -284,6 +284,7 @@ export function getLanguageServerToolPath(): string {
 	}
 	const alternateTools = goConfig['alternateTools'];
 	if (alternateTools) {
+		console.log('alternateTools ' + JSON.stringify(alternateTools, null, 2));
 		// The user's alternate language server was not found.
 		const goplsAlternate = alternateTools['gopls'];
 		if (goplsAlternate) {
@@ -298,9 +299,11 @@ Please install it and reload this VS Code window.`
 		if (alternateTools['go-langserver']) {
 			vscode.window.showErrorMessage(`Support for "go-langserver" has been deprecated.
 The recommended language server is gopls. Delete the alternate tool setting for "go-langserver" to use gopls, or change "go-langserver" to "gopls" in your settings.json and reload the VS Code window.`);
+			return;
 		}
-		return;
 	}
+
+	console.log('promptForMissingTools(gopls)');
 	// Prompt the user to install gopls.
 	promptForMissingTool('gopls');
 }