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fix: usage of potentially wrong melos version during script execution #783

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fix: usage of potentially wrong melos version during script execution #783

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c040977
Executes scripts with same dart/melos combination as currently running
bspinner Oct 29, 2024
c1f5d00
Fixes analysis issues
bspinner Oct 29, 2024
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45 changes: 44 additions & 1 deletion packages/melos/lib/src/scripts.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
import 'package:collection/collection.dart';
import 'package:meta/meta.dart';

import 'common/platform.dart';
import 'common/utils.dart';
import 'common/validation.dart';
import 'package.dart';
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if (exec == null) {
return scriptCommand;
} else {
final execCommand = ['melos', 'exec'];
/// `dart melos.dart exec` or `melos exec` with absolute paths
final execCommand = [..._determineMelosExecutablePaths(), 'exec'];

if (exec.concurrency != null) {
execCommand.addAll(['--concurrency', '${exec.concurrency}']);
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}
}

/// Identifies path of currently running melos and reuses it for nested script execution.

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///
/// Starting melos by just calling `melos` via shell
/// would use the first found binary found in `$PATH`,
/// i.e. usually the globally activated version. If there is one.
///
/// This can cause issues when melos is started with `dart run melos`,
/// which will prefer the melos version specified via (dev_)dependencies.
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Melos should always run scripts etc with the version that is defined in dev_dependencies, even if it is started directly from the version on path.

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Oh, thanks for the quick review.

Is this a future enhancement request or already implemented? 🙂

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The overarching goal of this PR is to eliminate ambiguity and surprises in the build process of Dart/Flutter applications. In line with that, I believe it would be ideal for Melos to behave in a consistent and predictable way.

Here’s what I think could be considered "unexpected" behavior:

  • If Melos uses different versions of itself for script execution (i.e. for subprocesses of itself)
    • This will be addressed with this PR!? :)
  • If Melos silently switches to a different version at startup (i.e., in the main process)
    • This could be especially challenging when intentionally testing a specific version.
    • Perhaps an optional strict mode (e.g., for CI environments) could help, where Melos would verify that its version matches the one specified in pubspec.lock.
      • The version in dev_dependencies might only define a minimum version, which wouldn’t fully address this, as you likely know as well. :)

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Is this a future enhancement request or already implemented? 🙂

It's already implemented, try pinning you melos version to an older version an see what happens. :)

The version in dev_dependencies might only define a minimum version, which wouldn’t fully address this, as you likely know as well. :)

If one wants a specific version of melos, why not just pin the version in pubspec? I don't see the need for any separate feature for this.

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@spydon Am I correct in understanding that you're unhappy with the comment in the code? If so, could you suggest a better or more accurate phrasing? :)

Additionally, if the only remaining blocker for merging is the failing tests, I’d be happy to look into the breaking cod – given it's likely the changes will be merged. :)

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I'm unsure if this is really needed/wanted, if I haven't misunderstood what this PR is trying to achieve.
If you run dart run melos --version you'll get the version specified in pubspec.yaml, which is the intentional behavior, no matter what melos binary that started it, the scripts should run with the melos version specified in the pubspec by the constraints.

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@bspinner any updated on this? Am I correct in that this PR would change so that it doesn't run with the melos version specified in the root pubspec?

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@bspinner bspinner Jan 20, 2025 •
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@spydon Sorry for the unexpected delay. Life is full of surprises... :|

According to my very basic knowledge of this codebase, this change does not interfere with anything happening during melos' start.
All it does is using the absolute path to the melos binary already running. So when melos starts itself another time for a script/command, the same melos binary will be used.
So this PR's changes apply to starting a subprocess, not melos' startup and checks. :)

Doing this differently could lead to heisenbugs, as behaviour could differ between directly executing a command and executing a command nested in another melos command.
Because which binary is used for the nested command execution currently depends on the user's shell environment.

Furthermore, it enables usage of melos in situations in which you don't have melos in your environmental PATH (which is the case in one of our CI environments).

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Life is full of surprises...

It is indeed, I hope you're all good!

Alright, that sounds like it makes sense, could you just add a test that runs melos --version inside of a script and checks that it is the same melos version as specified in the pubspec, if you pin a version in there.

/// So the initially started melos binary/script and the one used for melos script execution
/// could differ.
///
/// Besides ensuring starting the same melos as currently running,
/// this furthermore enables use of melos in environments
/// where `.pub-cache/bin` should/must not be put in `$PATH`.
List<String> _determineMelosExecutablePaths() {
final currentExecutablePathString = currentPlatform.resolvedExecutable;
final currentExecutablePathUri = Uri.file(currentExecutablePathString);
if (!currentExecutablePathUri.isAbsolute) {
throw 'Got invalid, unsupported or relative path to running executable. Expected absolute path.';

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}

final currentScriptPathUri = currentPlatform.script;
final currentScriptPathString = currentScriptPathUri.toFilePath();
if (!currentScriptPathString.isEmpty && !currentScriptPathUri.isAbsolute) {

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throw 'Got invalid, unsupported or relative path to melos. Expected absolute path.';

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}

// Determine if melos is running as script or compiled binary
final isScriptPathAvailable = !currentScriptPathString.isEmpty;

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final isCompiledMelosRunning =
currentExecutablePathUri == currentScriptPathUri;

if (!isScriptPathAvailable || isCompiledMelosRunning) {
return [currentExecutablePathString];
}

// currentExecutablePathString => path to dart binary
// currentScriptPathUri => path to melos.dart
return [currentExecutablePathString, currentScriptPathString];
}

/// Validates the script. Throws a [MelosConfigException] if the script is
/// invalid.
void validate() {
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