Add an opt-in for capturing sanitizer logs from the language server

Extension/.vscode/launch.json

@@ -22,6 +22,31 @@
             // you can use a watch task as a prelaunch task and it works like you'd want it to.
             "preLaunchTask": "watch"
         },
+        {
+            // debugs the extension with sanitizer (TSan/ASan/UBSan) reports captured to files.
+            // Requires a sanitizer build of the cpptools language server. Each process writes
+            // ${userHome}/cpptools-sanitizer-logs/<sanitizer>.<pid> (see readme.developer.md).
+            "name": "Run Extension (capture sanitizer logs)",
+            "type": "extensionHost",
+            "request": "launch",
+            "env": {
+                "CPPTOOLS_SANITIZER_LOG_DIR": "${userHome}/cpptools-sanitizer-logs"
+            },
+            "args": [
+                "--no-sandbox",
+                "--disable-updates",
+                "--skip-welcome",
+                "--skip-release-notes",
+                "--disable-workspace-trust",
+                "--extensionDevelopmentPath=${workspaceFolder}",
+            ],
+            "sourceMaps": true,
+            "outFiles": [
+                "${workspaceFolder}/dist/**"
+            ],
+            // you can use a watch task as a prelaunch task and it works like you'd want it to.
+            "preLaunchTask": "watch"
+        },
         {
             // debugs the extension (selecting the workspace)
             "name": "Run Extension-Select Workspace",

Extension/readme.developer.md

@@ -10,6 +10,7 @@
     - [From Inside VS Code](#from-inside-vs-code)
     - [From Command line](#from-command-line)
 - [Use of an isolated VS Code environment](#use-of-an-isolated-vs-code-environment)
+- [Capturing sanitizer diagnostics from the language server](#capturing-sanitizer-diagnostics-from-the-language-server)
 - [Testing](#testing)
     - [Unit tests](#unit-tests)
     - [Scenario Tests](#scenario-tests)
@@ -99,6 +100,39 @@ your normal VS Code environment.
 > When debugging the scenario tests from VS Code, it has to use the same VS Code binary 
 > as the debugger instance, so the isolated environment can't be used. 
 
+## Capturing sanitizer diagnostics from the language server
+
+When you run a sanitizer build of the language server (a `-tsan` or `-asan-ubsan` CMake preset --
+ThreadSanitizer, or AddressSanitizer + UndefinedBehaviorSanitizer combined; on Windows use
+`windows-x64-asan`, ASan only), the sanitizer prints its
+reports to `stderr`. Because the extension talks to the language server over `stdio`, those reports are
+easy to miss, and the exit-time backtrace you see in a crash log only shows the sanitizer shutting
+down -- not the actual report.
+
+To capture the reports, set the `CPPTOOLS_SANITIZER_LOG_DIR` environment variable before launching
+VS Code (or add it to the `env` of the launch config that starts the extension). The extension then
+routes each sanitizer's `log_path` into that directory, so every process -- `cpptools` and the
+`cpptools-srv`/`cpptools-srv2` children it spawns, which inherit the environment -- writes its own
+`<dir>/<sanitizer>.<pid>` file (for example `tsan.12345`). Any `TSAN_OPTIONS`/`ASAN_OPTIONS`/
+`UBSAN_OPTIONS` you already set are preserved.
+
+```bash
+# macOS/Linux
+export CPPTOOLS_SANITIZER_LOG_DIR=/tmp/cpptools-san
+# ...launch VS Code with a sanitizer build of cpptools, reproduce the issue, then read the logs.
+# A -tsan build writes tsan.<pid>; a combined -asan-ubsan build writes both asan.<pid> and ubsan.<pid>.
+cat /tmp/cpptools-san/*
+```
+
+The **Run Extension (capture sanitizer logs)** configuration in `.vscode/launch.json` sets this
+variable for you (to `${userHome}/cpptools-sanitizer-logs`), so you can just pick it from the Run
+and Debug dropdown instead of exporting the variable yourself.
+
+The variable is opt-in: when it is unset (normal development, CI, released builds) the child
+environment is inherited unchanged, so there is no behavior change. No debugger is required -- and
+because the sanitizer writes to a file, you avoid the shutdown-time hangs that can occur when a
+debugger is attached to a sanitizer process as it exits.
+
 ## Testing
 The test architecture has been reorganized and the layout refactored a bit. 
 

Extension/src/LanguageServer/client.ts

@@ -1683,9 +1683,13 @@ export class DefaultClient implements Client {
             throw String('Missing binary at ' + serverModule);
         }
         const serverName: string = this.getName(this.rootFolder);
+        // Opt-in: when CPPTOOLS_SANITIZER_LOG_DIR is set, route sanitizer (TSan/ASan/UBSan) reports
+        // from a sanitizer build to files in that directory (see getSanitizerServerEnv). This is
+        // undefined -- i.e. the environment is inherited unchanged -- for normal builds.
+        const sanitizerServerEnv: NodeJS.ProcessEnv | undefined = getSanitizerServerEnv();
         const serverOptions: ServerOptions = {
-            run: { command: serverModule, options: { detached: false, cwd: util.getExtensionFilePath("bin") } },
-            debug: { command: serverModule, args: [serverName], options: { detached: true, cwd: util.getExtensionFilePath("bin") } }
+            run: { command: serverModule, options: { detached: false, cwd: util.getExtensionFilePath("bin"), env: sanitizerServerEnv } },
+            debug: { command: serverModule, args: [serverName], options: { detached: true, cwd: util.getExtensionFilePath("bin"), env: sanitizerServerEnv } }
         };
 
         // The IntelliSense process should automatically detect when AutoPCH is
@@ -4419,6 +4423,48 @@ function getLanguageServerFileName(): string {
     return path.resolve(util.getExtensionFilePath("bin"), extensionProcessName);
 }
 
+// Opt-in helper for capturing sanitizer (TSan/ASan/UBSan) diagnostics from a sanitizer build of
+// the language server. The sanitizers print their reports to stderr, which the language-server
+// stdio can swallow. When the CPPTOOLS_SANITIZER_LOG_DIR environment variable is set, this routes
+// each sanitizer's log_path into that directory so every process -- cpptools and its
+// cpptools-srv/-srv2 children, which inherit this environment -- writes its own
+// "<dir>/<sanitizer>.<pid>" file. Any *SAN_OPTIONS the developer already set are preserved.
+// Returns undefined when the variable is unset, leaving the child environment inherited unchanged,
+// so this is a no-op for normal builds and safe to leave checked in. To use it, build a sanitizer
+// preset of the language server, set CPPTOOLS_SANITIZER_LOG_DIR before launching VS Code (or add it
+// to the launch config's "env"), reproduce, then read the "<dir>/<sanitizer>.<pid>" files.
+function getSanitizerServerEnv(): NodeJS.ProcessEnv | undefined {
+    const logDirectoryEnv: string | undefined = process.env.CPPTOOLS_SANITIZER_LOG_DIR;
+    if (!logDirectoryEnv) {
+        return undefined;
+    }
+    // The language server is spawned with cwd set to the "bin" directory (see the ServerOptions
+    // above), so the sanitizer runtime would interpret a relative log_path relative to "bin".
+    // Resolve against that same directory here so the directory we create and the path we hand the
+    // sanitizer always agree, and so a relative CPPTOOLS_SANITIZER_LOG_DIR still works.
+    const logDirectory: string = path.resolve(util.getExtensionFilePath("bin"), logDirectoryEnv);
+    // The sanitizer runtime opens "<log_path>.<pid>" and does not create missing directories, so
+    // ensure the directory exists (best effort). If it can't be created the sanitizer just falls
+    // back to stderr.
+    try {
+        fs.mkdirSync(logDirectory, { recursive: true });
+    } catch {
+        // Not fatal -- reports will go to stderr instead.
+    }
+    const withLogPath = (existingOptions: string | undefined, sanitizer: string): string =>
+        // The sanitizer runtime flag parser treats a space (as well as ',', ':', tab, and newline)
+        // as a delimiter between key=value pairs, so a single space is a valid, cross-platform
+        // separator here. Do not use path.delimiter (';' on Windows), which the parser does NOT
+        // treat as a delimiter and which would break parsing for the Windows ASan preset.
+        [existingOptions, `log_path=${path.join(logDirectory, sanitizer)}`].filter(Boolean).join(" ");
+    return {
+        ...process.env,
+        TSAN_OPTIONS: withLogPath(process.env.TSAN_OPTIONS, "tsan"),
+        ASAN_OPTIONS: withLogPath(process.env.ASAN_OPTIONS, "asan"),
+        UBSAN_OPTIONS: withLogPath(process.env.UBSAN_OPTIONS, "ubsan")
+    };
+}
+
 /* eslint-disable @typescript-eslint/no-unused-vars */
 class NullClient implements Client {
     private booleanEvent = new vscode.EventEmitter<boolean>();