move logic that locates the dart SDK to the analyzer package

[sigmundch]

The logic currently in code_transformers may be useful to other packages that want to use the analyzer without using barback.

Something of this sort would be great:

import 'dart:convert' as convert;
import 'dart:io' show File, Link, Platform, Process;
import 'package:path/path.dart' as path;

/// Attempts to provide the current Dart SDK directory. Returns null if the SDK
/// cannot be found.
String get dartSdkDirectory {
  bool isSdkDir(String dirname) =>
      new File(path.join(dirname, 'lib', '_internal', 'libraries.dart'))
      .existsSync();

  String executable = Platform.executable;
  if (path.split(executable).length == 1) {
    // TODO: do something else in windows...
    executable = Process
        .runSync('which', ['dart'], stdoutEncoding: convert.UTF8).stdout.trim();
    // In case Dart is symlinked (e.g. homebrew on Mac) follow symbolic links.
    var link = new Link(executable);
    if (link.existsSync()) {
      executable = link.resolveSymbolicLinksSync();
    }
    var sdkDir = path.dirname(path.dirname(executable));
    if (isSdkDir(sdkDir)) return sdkDir;
  }

  var dartDir = path.dirname(path.absolute(executable));
  // If there's a sub-dir named dart-sdk then we're most likely executing from
  // a dart enlistment build directory.
  if (isSdkDir(path.join(dartDir, 'dart-sdk'))) {
    return path.join(dartDir, 'dart-sdk');
  }
  // If we can find libraries.dart then it's the root of the SDK.
  if (isSdkDir(dartDir)) return dartDir;

  var parts = path.split(dartDir);
  // If the dart executable is within the sdk dir then get the root.
  if (parts.contains('dart-sdk')) {
    var dartSdkDir = path.joinAll(parts.take(parts.indexOf('dart-sdk') + 1));
    if (isSdkDir(dartSdkDir)) return dartSdkDir;
  }

  return null;
}

[sigmundch]

I'm happy to move our current code, just need some guidance as to where in the package it should live.

[DartBot]

This comment was originally written by @zoechi

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What about moving it to dart:io to make it even more widely available.
See also dart-archive/angular.dart#1270

[DartBot]

This comment was originally written by @zoechi

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Seems also related https://codereview.chromium.org/737033002/

[bwilkerson]

Moving it to dart:io is an appealing option.

If we want it to be in analyzer, then it probably belongs in the class DirectoryBasedDartSdk, probably as a replacement for the defaultSdkDirectory getter.

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Removed Priority-Unassigned label.
Added Priority-Medium label.

[sigmundch]

+Library-IO

That's an interesting idea - dart:io team - what are your thoughts?

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Removed Area-Analyzer label.
Added Area-Library, Library-IO labels.

[sethladd]

See also https://code.google.com/p/dart/issues/detail?id=21225

[DartBot]

This comment was originally written by @zoechi

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See also http://dartbug.com/16994

[sigmundch]

yeah - I think you are right, I'll mark 16994 as a duplicate of this, because that's basically what we want to do.

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Added Duplicate label.
Marked as being merged into #16994.