[debug] pretty print async context tree when extending a stack trace

Author: jbunton-atlassian

debug.js

@@ -6,6 +6,54 @@ function debug(msg) {
   fs.writeSync(1, 'trace.js DEBUG ' + msg + '\n');
 }
 
+function printRootTraces(traces) {
+  const rootAsyncIds = findRootAsyncIds(traces);
+  for (const asyncId of rootAsyncIds) {
+    printTree(traces, traces.get(asyncId));
+  }
+}
+
+function findRootAsyncIds(traces) {
+  const asyncIds = new Set(traces.keys());
+  for (const trace of traces.values()) {
+    for (const notRootTrace of trace.relatedTraces) {
+      asyncIds.delete(notRootTrace.asyncId);
+    }
+  }
+  return asyncIds;
+}
+
+function printTree(traces, trace, indent='', isLast=true, visited=new Set()) {
+  let line = indent + '\\-' + trace.asyncId;
+
+  if (isLast) {
+    indent += ' ';
+  } else {
+    indent += '| ';
+  }
+
+  if (!traces.get(trace.asyncId)) {
+    line += ' (not-root)';
+  }
+
+  if (visited.has(trace.asyncId)) {
+    line += ' (cycle)';
+  }
+
+  fs.writeSync(1, line + '\n');
+
+  if (visited.has(trace.asyncId)) {
+    return;
+  }
+  visited.add(trace.asyncId);
+
+  for (let i = 0; i < trace.relatedTraces.length; ++i) {
+    const isLast = i === trace.relatedTraces.length - 1;
+    printTree(traces, trace.relatedTraces[i], indent, isLast, visited);
+  }
+}
+
 module.exports = {
-  debug
+  debug,
+  printRootTraces
 };

trace.js

@@ -1,7 +1,7 @@
 'use strict';
 
 const DEBUG = false;
-const {debug} = DEBUG ? require('./debug') : {};
+const {printRootTraces, debug} = DEBUG ? require('./debug') : {};
 
 // Arbitrarily limit ourselves so we don't use up all memory on storing stack traces
 const MAX_RELATED_TRACES = 10;
@@ -53,6 +53,7 @@ function extendFrames(error, frames) {
 
   if (DEBUG) {
     debug(`extending: ${asyncId} with ${trace.stacks.map(({asyncId}) => asyncId)}`);
+    printRootTraces(traces);
   }
 
   for (const stack of trace.stacks) {