export function describeNativeComponentFrame()

in packages/shared/ReactComponentStackFrame.js [66:211]

• 100 lines of code
• 39 McCabe index (conditional complexity)

export function describeNativeComponentFrame(
  fn: Function,
  construct: boolean,
): string {
  // If something asked for a stack inside a fake render, it should get ignored.
  if (disableNativeComponentFrames || !fn || reentry) {
    return '';
  }

  if (__DEV__) {
    const frame = componentFrameCache.get(fn);
    if (frame !== undefined) {
      return frame;
    }
  }

  let control;

  reentry = true;
  const previousPrepareStackTrace = Error.prepareStackTrace;
  // $FlowFixMe It does accept undefined.
  Error.prepareStackTrace = undefined;
  let previousDispatcher;
  if (__DEV__) {
    previousDispatcher = ReactCurrentDispatcher.current;
    // Set the dispatcher in DEV because this might be call in the render function
    // for warnings.
    ReactCurrentDispatcher.current = null;
    disableLogs();
  }
  try {
    // This should throw.
    if (construct) {
      // Something should be setting the props in the constructor.
      const Fake = function() {
        throw Error();
      };
      // $FlowFixMe
      Object.defineProperty(Fake.prototype, 'props', {
        set: function() {
          // We use a throwing setter instead of frozen or non-writable props
          // because that won't throw in a non-strict mode function.
          throw Error();
        },
      });
      if (typeof Reflect === 'object' && Reflect.construct) {
        // We construct a different control for this case to include any extra
        // frames added by the construct call.
        try {
          Reflect.construct(Fake, []);
        } catch (x) {
          control = x;
        }
        Reflect.construct(fn, [], Fake);
      } else {
        try {
          Fake.call();
        } catch (x) {
          control = x;
        }
        fn.call(Fake.prototype);
      }
    } else {
      try {
        throw Error();
      } catch (x) {
        control = x;
      }
      fn();
    }
  } catch (sample) {
    // This is inlined manually because closure doesn't do it for us.
    if (sample && control && typeof sample.stack === 'string') {
      // This extracts the first frame from the sample that isn't also in the control.
      // Skipping one frame that we assume is the frame that calls the two.
      const sampleLines = sample.stack.split('\n');
      const controlLines = control.stack.split('\n');
      let s = sampleLines.length - 1;
      let c = controlLines.length - 1;
      while (s >= 1 && c >= 0 && sampleLines[s] !== controlLines[c]) {
        // We expect at least one stack frame to be shared.
        // Typically this will be the root most one. However, stack frames may be
        // cut off due to maximum stack limits. In this case, one maybe cut off
        // earlier than the other. We assume that the sample is longer or the same
        // and there for cut off earlier. So we should find the root most frame in
        // the sample somewhere in the control.
        c--;
      }
      for (; s >= 1 && c >= 0; s--, c--) {
        // Next we find the first one that isn't the same which should be the
        // frame that called our sample function and the control.
        if (sampleLines[s] !== controlLines[c]) {
          // In V8, the first line is describing the message but other VMs don't.
          // If we're about to return the first line, and the control is also on the same
          // line, that's a pretty good indicator that our sample threw at same line as
          // the control. I.e. before we entered the sample frame. So we ignore this result.
          // This can happen if you passed a class to function component, or non-function.
          if (s !== 1 || c !== 1) {
            do {
              s--;
              c--;
              // We may still have similar intermediate frames from the construct call.
              // The next one that isn't the same should be our match though.
              if (c < 0 || sampleLines[s] !== controlLines[c]) {
                // V8 adds a "new" prefix for native classes. Let's remove it to make it prettier.
                let frame = '\n' + sampleLines[s].replace(' at new ', ' at ');

                // If our component frame is labeled "<anonymous>"
                // but we have a user-provided "displayName"
                // splice it in to make the stack more readable.
                if (fn.displayName && frame.includes('<anonymous>')) {
                  frame = frame.replace('<anonymous>', fn.displayName);
                }

                if (__DEV__) {
                  if (typeof fn === 'function') {
                    componentFrameCache.set(fn, frame);
                  }
                }
                // Return the line we found.
                return frame;
              }
            } while (s >= 1 && c >= 0);
          }
          break;
        }
      }
    }
  } finally {
    reentry = false;
    if (__DEV__) {
      ReactCurrentDispatcher.current = previousDispatcher;
      reenableLogs();
    }
    Error.prepareStackTrace = previousPrepareStackTrace;
  }
  // Fallback to just using the name if we couldn't make it throw.
  const name = fn ? fn.displayName || fn.name : '';
  const syntheticFrame = name ? describeBuiltInComponentFrame(name) : '';
  if (__DEV__) {
    if (typeof fn === 'function') {
      componentFrameCache.set(fn, syntheticFrame);
    }
  }
  return syntheticFrame;
}