The log says why Android ended the last run

Native crashes, freezes and the memory killer leave no stack trace in the log. On
the next launch, Gearslip writes the reason Android recorded, at the end of the run
that died and in the new one.

gearslip/src/main/java/app/seb3thehacker/gearslip/GearslipLog.kt

@@ -54,9 +54,65 @@ object GearslipLog {
         SessionReport.init(context)
         // One file per launch adds up; the newest are the ones anyone asks for.
         io.execute { logFiles(dir).drop(KEEP_FILES).forEach { it.delete() } }
+        lastExit(context, dir)
     }
 
     private const val KEEP_FILES = 30
+    private const val KEY_EXIT_SEEN = "log_exit_seen"
+
+    /**
+     * Why Android ended the last run, when the crash handler can't have seen it: a native crash,
+     * a freeze (ANR), or the memory killer. Written here and onto the end of that run's own log,
+     * which is the one a driver shares after a drive that went wrong.
+     */
+    private fun lastExit(context: Context, dir: File) {
+        val am = context.getSystemService(android.app.ActivityManager::class.java) ?: return
+        val seen = AppSettings.getString(context, KEY_EXIT_SEEN, "0").toLongOrNull() ?: 0L
+        val exits = runCatching { am.getHistoricalProcessExitReasons(null, 0, 5) }.getOrDefault(emptyList())
+            .filter { it.timestamp > seen }
+        exits.firstOrNull()?.let { AppSettings.putString(context, KEY_EXIT_SEEN, it.timestamp.toString()) }
+        val parse = SimpleDateFormat("yyyyMMdd-HHmmss", Locale.US)
+        for (exit in exits.reversed()) {
+            val why = EXIT_REASONS[exit.reason] ?: continue
+            val at = SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.US).format(Date(exit.timestamp))
+            val detail = buildString {
+                append("$at, $why")
+                exit.description?.takeIf { it.isNotBlank() }?.let { append(" ($it)") }
+                append(", memory ${exit.pss / 1024} MB")
+                if (exit.reason == android.app.ApplicationExitInfo.REASON_ANR) {
+                    anrMainThread(exit)?.let { append("\n").append(it) }
+                }
+            }
+            w("Android ended an earlier run at $detail")
+            // The run that died: the newest log that started before it ended.
+            val run = logFiles(dir).filter { it != file }.firstOrNull { f ->
+                val started = runCatching { parse.parse(f.name.removePrefix("gearslip-").removeSuffix(".log")) }.getOrNull()
+                started != null && started.time <= exit.timestamp
+            } ?: continue
+            io.execute { runCatching { run.appendText("--- $EXIT_MARK $detail\n") } }
+        }
+    }
+
+    /** The main thread's stack from an ANR trace: what Gearslip was stuck doing. */
+    private fun anrMainThread(exit: android.app.ApplicationExitInfo): String? = runCatching {
+        exit.traceInputStream?.bufferedReader()?.useLines { lines ->
+            lines.dropWhile { !it.startsWith("\"main\"") }.take(ANR_LINES).joinToString("\n")
+        }?.takeIf { it.isNotBlank() }
+    }.getOrNull()
+
+    private const val ANR_LINES = 25
+    private const val EXIT_MARK = "Android ended this run:"
+
+    /** Exit reasons worth a line; leaving, updating and Java crashes (already logged) aren't. */
+    private val EXIT_REASONS = mapOf(
+        android.app.ApplicationExitInfo.REASON_CRASH_NATIVE to "a native crash",
+        android.app.ApplicationExitInfo.REASON_ANR to "the app stopped responding (ANR)",
+        android.app.ApplicationExitInfo.REASON_LOW_MEMORY to "the phone ran low on memory",
+        android.app.ApplicationExitInfo.REASON_EXCESSIVE_RESOURCE_USAGE to "it used too much of the phone's resources",
+        android.app.ApplicationExitInfo.REASON_INITIALIZATION_FAILURE to "it failed to start",
+        android.app.ApplicationExitInfo.REASON_SIGNALED to "the system killed it",
+        android.app.ApplicationExitInfo.REASON_DEPENDENCY_DIED to "something it depends on died",
+    )
 
     private fun logFiles(dir: File): List<File> =
         dir.listFiles { f -> f.isFile && f.name.startsWith("gearslip-") && f.name.endsWith(".log") }
@@ -77,7 +133,7 @@ object GearslipLog {
             PastLog(
                 file = f,
                 started = runCatching { parse.parse(f.name.removePrefix("gearslip-").removeSuffix(".log")) }.getOrNull(),
-                crashed = "FATAL uncaught" in text,
+                crashed = "FATAL uncaught" in text || EXIT_MARK in text,
                 car = Regex("""car="([^"]+)"""").findAll(text).lastOrNull()?.groupValues?.get(1),
             )
         }