Add `pub get|upgrade|downgrade --json` that prints errors in a machine-readable format

[srawlins]

The analysis server runs dart pub get (or upgrade) in a synthetic pub package directory for analyzer plugins. If that command fails (like a plugin has a version constraint of it's dependency on analysis_server_plugin which is incompatible with DAS's constraint, or two plugins have incompatible constraints of their dependencies on analysis_server_plugin, etc.) then DAS just takes the stderr/stdout and dumps it to the user, like if they are executing dart analyze.

A user pointed out, dart-lang/sdk#63568, that much of the recommendations in the error text are inapplicable to the user, and actively lead them astray.

It would be great if DAS could instead call dart pub get --json or something similar, which would spit out its errors in a machine-readable format.

(Alternatively, DAS could execute dart pub get via a programmatic API, but I'm unaware that one exists. That would probably be faster and we'd have more fine-grained control. I'm sure that's a huge ask if it's not available today.)

CC @bwilkerson @keertip

[sigurdm]

We have a small programmatic api, namely ensurePubspecResolved

pub/lib/pub.dart

Line 75 in ac14a82

Future<void> ensurePubspecResolved(

that is doing a "smart" check if the resolution looks up to date (are timestamps in order) and if not runs what corresponds to pub get.
pub is already part of the dartdev snapshot. Not sure if the analyzer is in the same snapshot? Otherwise there would be a size-cost in including it into the dart code. This function has no "upgrade" mode.

Not sure the output is what you need. What part of the output would you like to present to the user? Do you have a suggestion for the json output.

[srawlins]

Based on this stderr from dart pub get:

Because analysis_server_plugin >=0.3.8 <0.3.9 depends on analyzer_plugin 0.14.2 and analysis_server_plugin >=0.3.9 <0.3.10 depends on analyzer_plugin 0.14.3, analysis_server_plugin >=0.3.8 <0.3.10 requires analyzer_plugin 0.14.2 or 0.14.3.
And because analysis_server_plugin >=0.3.10 <0.3.11 depends on analyzer_plugin 0.14.4, analysis_server_plugin >=0.3.8 <0.3.11 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4.
And because analysis_server_plugin >=0.3.11 <0.3.13 depends on analyzer_plugin 0.14.5 and analysis_server_plugin >=0.3.13 <0.3.14 depends on analyzer_plugin 0.14.7, analysis_server_plugin >=0.3.8 <0.3.14 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4 or 0.14.5 or 0.14.7.
And because analysis_server_plugin >=0.3.14 <0.3.15 depends on analyzer_plugin 0.14.8 and analysis_server_plugin >=0.3.15 <0.3.16 depends on analyzer_plugin 0.14.9, analysis_server_plugin >=0.3.8 <0.3.16 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4 or 0.14.5 or 0.14.7 or 0.14.8 or 0.14.9.
And because analysis_server_plugin >=0.3.16 depends on analyzer_plugin 0.14.10 and riverpod_lint >=3.1.0 <3.1.4-dev.1 depends on analyzer_plugin ^0.13.10, riverpod_lint >=3.1.0 <3.1.4-dev.1 is incompatible with analysis_server_plugin >=0.3.8.
So, because plugin_entrypoint depends on both analysis_server_plugin ^0.3.8 and riverpod_lint 3.1.0, version solving failed.


You can try one of the following suggestions to make the pubspec resolve:
* Try upgrading your constraint on riverpod_lint: dart pub add riverpod_lint:^3.1.4-dev.3
* Consider downgrading your constraint on analysis_server_plugin: dart pub add analysis_server_plugin:^0.3.3

I think something like this JSON would be nice:

{
  causes: {
    "Because analysis_server_plugin >=0.3.8 <0.3.9 depends on analyzer_plugin 0.14.2 and analysis_server_plugin >=0.3.9 <0.3.10 depends on analyzer_plugin 0.14.3, analysis_server_plugin >=0.3.8 <0.3.10 requires analyzer_plugin 0.14.2 or 0.14.3.",
    "And because analysis_server_plugin >=0.3.10 <0.3.11 depends on analyzer_plugin 0.14.4, analysis_server_plugin >=0.3.8 <0.3.11 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4.",
    "And because analysis_server_plugin >=0.3.11 <0.3.13 depends on analyzer_plugin 0.14.5 and analysis_server_plugin >=0.3.13 <0.3.14 depends on analyzer_plugin 0.14.7, analysis_server_plugin >=0.3.8 <0.3.14 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4 or 0.14.5 or 0.14.7.",
    "And because analysis_server_plugin >=0.3.14 <0.3.15 depends on analyzer_plugin 0.14.8 and analysis_server_plugin >=0.3.15 <0.3.16 depends on analyzer_plugin 0.14.9, analysis_server_plugin >=0.3.8 <0.3.16 requires analyzer_plugin 0.14.2 or 0.14.3 or 0.14.4 or 0.14.5 or 0.14.7 or 0.14.8 or 0.14.9.",
    "And because analysis_server_plugin >=0.3.16 depends on analyzer_plugin 0.14.10 and riverpod_lint >=3.1.0 <3.1.4-dev.1 depends on analyzer_plugin ^0.13.10, riverpod_lint >=3.1.0 <3.1.4-dev.1 is incompatible with analysis_server_plugin >=0.3.8.",
    "So, because plugin_entrypoint depends on both analysis_server_plugin ^0.3.8 and riverpod_lint 3.1.0, version solving failed."
  },
  suggestions: {
    "Try upgrading your constraint on riverpod_lint: dart pub add riverpod_lint:^3.1.4-dev.3",
    "Consider downgrading your constraint on analysis_server_plugin: dart pub add analysis_server_plugin:^0.3.3",
  }
}

The data could be broken down further, but this textual breakdown is all we'd need, I think. DAS could print the causes, and then print our own suggestions. If the data was broken down further, DAS could see instances of what plugin_entrypoint are found, and the names of plugins that DAS enabled, like riverpod_lint. So maybe a cause could be broken down into:

{
  causes: {
    "analysis_server_plugin >= 0.3.16": /* depends on */ "analyzer_plugin 0.14.10",
    "riverpod_lint >= 3.1.0 <3.1.4-dev.1": /* depends on */ "analyzer_plugin ^0.13.10"
  },
  "resulting incompatibilities": {
    "riverpod_lint >=3.1.0 <3.1.4-dev.1": /* is incompatible with */ "analysis_server_plugin >=0.3.8"
  }
}