Try to find a valid dotnet version from the path before falling back …

…to runtime extension

src/lsptoolshost/dotnetRuntimeExtensionResolver.ts

@@ -5,12 +5,16 @@
 
 import * as path from 'path';
 import * as vscode from 'vscode';
+import * as semver from 'semver';
 import { HostExecutableInformation } from '../shared/constants/hostExecutableInformation';
 import { IHostExecutableResolver } from '../shared/constants/IHostExecutableResolver';
 import { PlatformInformation } from '../shared/platform';
 import { Options } from '../shared/options';
 import { existsSync } from 'fs';
 import { CSharpExtensionId } from '../constants/csharpExtensionId';
+import { promisify } from 'util';
+import { exec } from 'child_process';
+import { pathExistsSync } from 'fs-extra';
 
 export const DotNetRuntimeVersion = '7.0';
 
@@ -22,19 +26,35 @@ interface IDotnetAcquireResult {
  * Resolves the dotnet runtime for a server executable from given options and the dotnet runtime VSCode extension.
  */
 export class DotnetRuntimeExtensionResolver implements IHostExecutableResolver {
+    private readonly minimumDotnetVersion = '7.0.100';
     constructor(
         private platformInfo: PlatformInformation,
         /**
          * This is a function instead of a string because the server path can change while the extension is active (when the option changes).
          */
-        private getServerPath: (options: Options, platform: PlatformInformation) => string
+        private getServerPath: (options: Options, platform: PlatformInformation) => string,
+        private channel: vscode.OutputChannel
     ) {}
 
     private hostInfo: HostExecutableInformation | undefined;
 
     async getHostExecutableInfo(options: Options): Promise<HostExecutableInformation> {
         let dotnetRuntimePath = options.commonOptions.dotnetPath;
         const serverPath = this.getServerPath(options, this.platformInfo);
+
+        // Check if we can find a valid dotnet from dotnet --version on the PATH.
+        if (!dotnetRuntimePath) {
+            const dotnetPath = await this.findDotnetFromPath();
+            if (dotnetPath) {
+                return {
+                    version: '' /* We don't need to know the version - we've already verified its high enough */,
+                    path: dotnetPath,
+                    env: process.env,
+                };
+            }
+        }
+
+        // We didn't find it on the path, see if we can install the correct runtime using the runtime extension.
         if (!dotnetRuntimePath) {
             const dotnetInfo = await this.acquireDotNetProcessDependencies(serverPath);
             dotnetRuntimePath = path.dirname(dotnetInfo.path);
@@ -101,4 +121,55 @@ export class DotnetRuntimeExtensionResolver implements IHostExecutableResolver {
 
         return dotnetInfo;
     }
+
+    /**
+     * Checks dotnet --version to see if the value on the path is greater than the minimum required version.
+     * This is adapated from similar O# server logic and should be removed when we have a stable acquisition extension.
+     * @returns true if the dotnet version is greater than the minimum required version, false otherwise.
+     */
+    private async findDotnetFromPath(): Promise<string | undefined> {
+        try {
+            // Run dotnet version to see if there is a valid dotnet on the path with a high enough version.
+            const result = await promisify(exec)(`dotnet --version`);
+
+            if (result.stderr) {
+                throw new Error(`Unable to read dotnet version information. Error ${result.stderr}`);
+            }
+
+            const dotnetVersion = semver.parse(result.stdout.trimEnd());
+            if (!dotnetVersion) {
+                throw new Error(`Unknown result output from 'dotnet --version'. Received ${result.stdout}`);
+            }
+
+            if (semver.lt(dotnetVersion, this.minimumDotnetVersion)) {
+                throw new Error(
+                    `Found dotnet version ${dotnetVersion}. Minimum required version is ${this.minimumDotnetVersion}.`
+                );
+            }
+
+            // Find the location of the dotnet on path.
+            const command = this.platformInfo.isWindows() ? 'where' : 'which';
+            const whereOutput = await promisify(exec)(`${command} dotnet`);
+            if (!whereOutput.stdout) {
+                throw new Error(`Unable to find dotnet from where.`);
+            }
+
+            const path = whereOutput.stdout.trim();
+            if (!pathExistsSync(path)) {
+                throw new Error(`dotnet path does not exist: ${path}`);
+            }
+
+            this.channel.appendLine(`Using dotnet configured on PATH`);
+            return path;
+        } catch (e) {
+            this.channel.appendLine(
+                'Failed to find dotnet info from path, falling back to acquire runtime via ms-dotnettools.vscode-dotnet-runtime'
+            );
+            if (e instanceof Error) {
+                this.channel.appendLine(e.message);
+            }
+        }
+
+        return undefined;
+    }
 }

src/lsptoolshost/roslynLanguageServer.ts

@@ -733,7 +733,7 @@ export async function activateRoslynLanguageServer(
     // Create a separate channel for outputting trace logs - these are incredibly verbose and make other logs very difficult to see.
     _traceChannel = vscode.window.createOutputChannel('C# LSP Trace Logs');
 
-    const hostExecutableResolver = new DotnetRuntimeExtensionResolver(platformInfo, getServerPath);
+    const hostExecutableResolver = new DotnetRuntimeExtensionResolver(platformInfo, getServerPath, outputChannel);
     const additionalExtensionPaths = scanExtensionPlugins();
     _languageServer = new RoslynLanguageServer(
         platformInfo,