packages/flutter/lib/src/foundation/debug.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';

import 'assertions.dart';
import 'platform.dart';
import 'print.dart';

/// Returns true if none of the foundation library debug variables have been
/// changed.
///
/// This function is used by the test framework to ensure that debug variables
/// haven't been inadvertently changed.
///
/// The `debugPrintOverride` argument can be specified to indicate the expected
/// value of the [debugPrint] variable. This is useful for test frameworks that
/// override [debugPrint] themselves and want to check that their own custom
/// value wasn't overridden by a test.
///
/// See [the foundation library](foundation/foundation-library.html)
/// for a complete list.
bool debugAssertAllFoundationVarsUnset(String reason, { DebugPrintCallback debugPrintOverride = debugPrintThrottled }) {
  assert(() {
    if (debugPrint != debugPrintOverride ||
        debugDefaultTargetPlatformOverride != null ||
        debugDoublePrecision != null)
      throw FlutterError(reason);
    return true;
  }());
  return true;
}

/// Boolean value indicating whether [debugInstrumentAction] will instrument
/// actions in debug builds.
bool debugInstrumentationEnabled = false;

/// Runs the specified [action], timing how long the action takes in debug
/// builds when [debugInstrumentationEnabled] is true.
///
/// The instrumentation will be printed to the logs using [debugPrint]. In
/// non-debug builds, or when [debugInstrumentationEnabled] is false, this will
/// run [action] without any instrumentation.
///
/// Returns the result of running [action].
///
/// See also:
///
///  * [Timeline], which is used to record synchronous tracing events for
///    visualization in Chrome's tracing format. This method does not
///    implicitly add any timeline events.
Future<T> debugInstrumentAction<T>(String description, Future<T> action()) {
  bool instrument = false;
  assert(() {
    instrument = debugInstrumentationEnabled;
    return true;
  }());
  if (instrument) {
    final Stopwatch stopwatch = Stopwatch()..start();
    return action().whenComplete(() {
      stopwatch.stop();
      debugPrint('Action "$description" took ${stopwatch.elapsed}');
    });
  } else {
    return action();
  }
}

/// Argument passed to [Timeline] events in order to cause those events to be
/// shown in the developer-centric version of the Observatory Timeline.
///
/// See also:
///
///  * [Timeline.startSync], which typically takes this value as its `arguments`
///    argument.
const Map<String, String> timelineWhitelistArguments = <String, String>{
  'mode': 'basic',
};

/// Configure [debugFormatDouble] using [num.toStringAsPrecision].
///
/// Defaults to null, which uses the default logic of [debugFormatDouble].
int debugDoublePrecision;

/// Formats a double to have standard formatting.
///
/// This behavior can be overridden by [debugDoublePrecision].
String debugFormatDouble(double value) {
  if (value == null) {
    return 'null';
  }
  if (debugDoublePrecision != null) {
    return value.toStringAsPrecision(debugDoublePrecision);
  }
  return value.toStringAsFixed(1);
}