extension: use Delve's guess-substitute-path-helper when available

When the remote mode is specified try to call

	dlv guess-substitute-path-helper

and if it is available use its ouptut and switch to dlv-dap mode unless
otherwise specified.
The legacy adapter has been unmaintained for years and has known bugs
(for example, breakpoints can not be set while the program is running)
but couldn't be deleted because it implements automatic mappings of
source files.

Updates #3096, #3193

Change-Id: Ie2f731b149e0ba4d5031bb57d61e7b407c3a40f8
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/643280
Reviewed-by: Hongxiang Jiang <[email protected]>
kokoro-CI: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: aarzilli

extension/src/goDebugConfiguration.ts

@@ -33,6 +33,7 @@ import { parseEnvFiles } from './utils/envUtils';
 import { resolveHomeDir } from './utils/pathUtils';
 import { createRegisterCommand } from './commands';
 import { GoExtensionContext } from './context';
+import { spawn } from 'child_process';
 
 let dlvDAPVersionChecked = false;
 
@@ -182,12 +183,23 @@ export class GoDebugConfigurationProvider implements vscode.DebugConfigurationPr
 				debugConfiguration['debugAdapter'] = dlvConfig['debugAdapter'];
 			}
 		}
-		// If neither launch.json nor settings.json gave us the debugAdapter value, we go with the default
-		// from package.json (dlv-dap) unless this is remote attach with a stable release.
+
+		// If neither launch.json nor settings.json gave us the debugAdapter, we go with the default from pacakge.json (dlv-dap) for all modes except 'remote'.
+		// For remote we will use 'dlv-dap' if we can call 'dlv substitute-path-guess-helper' or 'legacy' otherwise.
 		if (!debugConfiguration['debugAdapter']) {
+			// set dlv-dap by default
 			debugConfiguration['debugAdapter'] = defaultConfig.debugAdapter.default;
-			if (debugConfiguration['mode'] === 'remote' && !extensionInfo.isPreview) {
-				debugConfiguration['debugAdapter'] = 'legacy';
+			if (debugConfiguration['mode'] === 'remote') {
+				const substitutePathGuess = await this.guessSubstitutePath();
+				if (substitutePathGuess === null) {
+					if (!extensionInfo.isPreview) {
+						// can't guess substitute path and isPreview isn't set, fall back to legacy.
+						debugConfiguration['debugAdapter'] = 'legacy';
+					}
+				} else {
+					debugConfiguration['debugAdapter'] = defaultConfig.debugAdapter.default;
+					debugConfiguration['guessSubstitutePath'] = substitutePathGuess;
+				}
 			}
 		}
 		if (debugConfiguration['debugAdapter'] === 'dlv-dap') {
@@ -372,6 +384,41 @@ export class GoDebugConfigurationProvider implements vscode.DebugConfigurationPr
 		return debugConfiguration;
 	}
 
+	/**
+	 * Calls `dlv substitute-path-guess-helper` to get a set of parameters used by Delve to guess the substitutePath configuration after also examining the executable.
+	 *
+	 * See https://github.com/go-delve/delve/blob/d5fb3bee427202f0d4b1683bf743bfd2adb41757/service/debugger/debugger.go#L2466
+	 */
+	private async guessSubstitutePath(): Promise<object | null> {
+		return new Promise((resolve) => {
+			const child = spawn(getBinPath('dlv'), ['substitute-path-guess-helper']);
+			let stdoutData = '';
+			let stderrData = '';
+			child.stdout.on('data', (data) => {
+				stdoutData += data;
+			});
+			child.stderr.on('data', (data) => {
+				stderrData += data;
+			});
+
+			child.on('close', (code) => {
+				if (code !== 0) {
+					resolve(null);
+				} else {
+					try {
+						resolve(JSON.parse(stdoutData));
+					} catch (error) {
+						resolve(null);
+					}
+				}
+			});
+
+			child.on('error', (error) => {
+				resolve(null);
+			});
+		});
+	}
+
 	public removeGcflags(args: string): { args: string; removed: boolean } {
 		// From `go help build`
 		// ...