fix(crashtracking): resolve frames out-of-process on Linux (#9237)

The Linux/non-Linux resolve mode selection compared `os.platform`, the
function reference, against the string 'linux'. That comparison is
always false, so Linux always fell through to
'EnabledWithInprocessSymbols' instead of the intended
'EnabledWithSymbolsInReceiver'. Out-of-process symbolication is the
only supported path on Linux (per the adjacent comment and the
crashtracking team's original guidance), so in-process symbolication
during a live crash could leave the crash report unwritten.

Call `platform()` so the real platform is evaluated. Add a unit test
asserting resolve_frames matches the running platform, which fails
against the old code on Linux.

Author: bengl

packages/dd-trace/src/crashtracking/crashtracker.js

@@ -1,6 +1,6 @@
 'use strict'
 
-const { EOL } = require('node:os')
+const { EOL, platform } = require('node:os')
 
 // Load binding first to not import other modules if it throws
 const libdatadog = require('@datadog/libdatadog')
@@ -71,7 +71,7 @@ class Crashtracker {
 
     // Out-of-process symbolication currently works on
     // Linux only, does not work on Mac.
-    const resolveMode = require('os').platform === 'linux'
+    const resolveMode = platform() === 'linux'
       ? 'EnabledWithSymbolsInReceiver'
       : 'EnabledWithInprocessSymbols'
 

packages/dd-trace/test/crashtracking/crashtracker.spec.js

@@ -89,6 +89,17 @@ describeNotWindows('crashtracker', () => {
       sinon.assert.calledOnce(binding.init)
     })
 
+    it('should resolve frames out-of-process on Linux and in-process elsewhere', () => {
+      crashtracker.start(config)
+
+      const initConfig = binding.init.firstCall.args[0]
+      const expected = os.platform() === 'linux'
+        ? 'EnabledWithSymbolsInReceiver'
+        : 'EnabledWithInprocessSymbols'
+
+      assert.strictEqual(initConfig.resolve_frames, expected)
+    })
+
     it('should handle unix sockets', () => {
       config.url = new URL('unix:///var/datadog/apm/test.socket')