check whether compiler lsp support compile project (microsoft#7374)

When leverage lsp to emit code, the lsp server need have the capacity of
internalCompile. Typespec compiler support this only after version
1.0.0. So check the lsp capacity before emit code, and provide clear
information to info user to upgrade their compiler.

Author: chunyu3

.chronus/changes/lspSupportCheck-2025-4-16-6-55-13.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - typespec-vscode
+---
+
+Check whether the compiler language server supports project compilation.

packages/typespec-vscode/src/vscode-cmd/emit-code/emit-code.ts

@@ -12,6 +12,7 @@ import { getDirectoryPath } from "../../path-utils.js";
 import telemetryClient from "../../telemetry/telemetry-client.js";
 import { OperationTelemetryEvent } from "../../telemetry/telemetry-event.js";
 import { resolveTypeSpecCli } from "../../tsp-executable-resolver.js";
+import { TspLanguageClient } from "../../tsp-language-client.js";
 import { ResultCode } from "../../types.js";
 import {
   formatDiagnostic,
@@ -460,6 +461,7 @@ async function doEmit(
           });
           return ResultCode.Fail;
         }
+
         const compileResult = await tspLanguageClient.compileProject(
           {
             uri: getVscodeUriFromPath(mainTspFile),
@@ -540,6 +542,25 @@ export async function emitCode(
   uri: vscode.Uri,
   tel: OperationTelemetryEvent,
 ): Promise<ResultCode> {
+  if (!tspLanguageClient) {
+    logger.error(
+      `LSP client is not started. Make sure typespec compiler has been installed. Emitting Cancelled.`,
+      [],
+      {
+        showOutput: true,
+        showPopup: true,
+      },
+    );
+    return ResultCode.Cancelled;
+  }
+  const isSupport = await isCompilerSupport(tspLanguageClient);
+  if (!isSupport) {
+    logger.info(
+      "Compiling project via the language server is not supported in the current version of TypeSpec Compiler. Emitting Cancelled.",
+    );
+    tel.lastStep = "Check compiler capability";
+    return ResultCode.Cancelled;
+  }
   let tspProjectFile: string = "";
   if (!uri) {
     const targetPathes = await TraverseMainTspFileInWorkspace();
@@ -797,3 +818,21 @@ export async function emitCode(
     }
   }
 }
+
+async function isCompilerSupport(client: TspLanguageClient): Promise<boolean> {
+  if (
+    client.initializeResult?.serverInfo?.version === undefined ||
+    client.initializeResult?.customCapacities?.internalCompile !== true
+  ) {
+    logger.error(
+      `Compiling project via the language server is not supported in the current version of TypeSpec Compiler (ver ${client.initializeResult?.serverInfo?.version ?? "<= 1.0.0"}). Please upgrade to a version later than 1.0.0 (by npm install @typespec/compiler) and try again.`,
+      [],
+      {
+        showOutput: true,
+        showPopup: true,
+      },
+    );
+    return false;
+  }
+  return true;
+}