Dart compilation errors in flutter app builds should have a more user friendly error message #125032
Description
When a Flutter app contains a library that doesn't have null safety -- because it has a // @dart=2.9 version maker -- the flutter run command fails with a very convoluted message:
mit-macbookpro7:unsoundflutter mit$ flutter run
Resolving dependencies...
+ characters 1.3.0
+ collection 1.17.1
+ flutter 0.0.0 from sdk flutter
+ js 0.6.7
+ material_color_utilities 0.2.0 (0.3.0 available)
+ meta 1.9.1
+ sky_engine 0.0.99 from sdk flutter
+ vector_math 2.1.4
Changed 8 dependencies!
Launching lib/main.dart on macOS in debug mode...
lib/unsound.dart:1:1: Error: Library doesn't support null safety.
// @dart=2.9
^^^^^^^^^^^^
Target kernel_snapshot failed: Exception
Command PhaseScriptExecution failed with a nonzero exit code
warning: Run script build phase 'Run Script' will be run during every build because it does not specify any outputs. To address this warning, either add output dependencies to the script phase, or configure it to run in every build by unchecking "Based on dependency analysis" in the script phase. (in target 'Flutter Assemble' from project 'Runner')
** BUILD FAILED **
Building macOS application...
Exception: Build process failed
Can we catch this specific error from the compiler and omit this part of the error output?
Target kernel_snapshot failed: Exception
Command PhaseScriptExecution failed with a nonzero exit code
warning: Run script build phase 'Run Script' will be run during every build because it does not specify any outputs. To address this warning, either add output dependencies to the script phase, or configure it to run in every build by unchecking "Based on dependency analysis" in the script phase. (in target 'Flutter Assemble' from project 'Runner')
** BUILD FAILED **
Building macOS application...
Exception: Build process failed