Unify syntax to define environment declarations (--define)

[Mabsten]

The syntax to define environment declarations (to read with String.fromEnvironment() method and relateds) is very divergent between the various tools/dart sub-commands:
(I tested the flags with Dart Sdk 2.12 (2.12.0-133.2.beta, on Windows x64))

dart2native / dart compile exe
use the -D/--define flag
(cfr https://dart.dev/tools/dart2native );

dart / dart run
does not support the define flags
UPDATE:
dart
supports the -D flag (also dart -D run is ok)
although it is not mentioned in the help and in the doc
(cfr https://dart.dev/tools/dart-vm );

dart2js
use only the -D flag;
(cfr https://dart.dev/tools/dart2js#options );

dart compile js
does not even support the -D flag, despite it being the substitute of the dart2js command (I think);

dartdevc -using webdev-
require to use a build.yaml file or this command-line syntax (not tested):
webdev serve -- '--define=build_web_compilers:ddc=environment={"SOME_VAR":"some_value"}'
(cfr https://dart.dev/tools/webdev and https://pub.dev/packages/build_web_compilers );

flutter (from the Sdk 1.17)
use the --dart-define flag.
The --dart-define flag is very useful in Flutter, for example to set a log level or an api token.

Wouldn't it be useful if all the sub-commands of the new dart tool supported the define flag? Or maybe I'm missing an alternative that already exists?

[srawlins]

I'll initially tag this as dart-cli; @devoncarew is there a plan to unify this flag?

[bkonyi]

There should be an effort to make this more consistent, and it's definitely an oversight that dart run -D isn't valid. At the very least, we should make sure that -D is accepted by the relevant commands (e.g., run, compile, test).

A temporary workaround is to provide -D before the CLI command as the VM will interpret those flags itself. This will work for the dart run case, but I'm not sure about the other commands.

[bkonyi]

@sigmundch can you or someone else take a look at the dart compile js case?

[Mabsten]

Thank you for the attention and for the tip about dart -D, I didn't know that (it was not mentioned in the help); then the -D flag is available for all the old tools, except dartdevc/webdev (which however supports the build.yaml approach).

This flag is very important in the build pipeline because it provides (in pair with fromEnvironment()) an equivalent of BuildConfig fields in the Android (Gradle) development and of environment variables in the Node/Javascript build pipeline (I think to Js package to inline env vars like envify).

That the need for such a mechanism is strongly felt in the Dart community is testified by the multitude of related issues opened (as Please document {String|int|bool}.fromEnvironment) and of Dart packages that try to emulate it in various ways (with code generation, multiple entry point files, etc.), but all with severe drawbacks (i.e. dotenv, flutter_dotenv, envify, dynamic_config_generator, flutter_config, env_vars, dotenv2dart, etc).
Dart's environment declarations, now that they are also supported in flutter, can replace all previous workarounds.
It would be great if with the introduction of the new general-purpouse dart tool the syntax were unified, in order to make -D similar to --dart-define in flutter run and flutter build.

[Mabsten]

Another syntax-related issue concerns comma support:

dart2js and dart (VM tool)
allow to insert the comma in an environment declaration value (also without quote, which are instead required for the space).

dart2native and dart compile exe (as flutter)
doesn't allow to insert the comma, not even using the quotes.
This has already been reported for the flutter tool.
dart2native and dart compile exe (as flutter) on the other hand allow the definition of many variables without repeating the flag, using the comma: example: dart compile exe --dart-define=MY_VAR1="first value",MY_VAR2="second value" (also without quotes, if the values don't contains spaces).
I guess the problem is that the parsing is stopped as soon as the comma is found even if the string is surrounded by the quotation marks (with the space instead the quotation marks work correctly ie they make the string be read completely).
Reproducible test:

//main.dart

void main() {
  const my_var = String.fromEnvironment("my_var", defaultValue: "not found");
  print("my_var: $my_var");
}

Compile the source with:
dart -Dmy_var="first value,second value" main.dart
dart2js -Dmy_var="first value,second value" main.dart
dart2native -Dmy_var="first value,second value" main.dart
dart compile exe -Dmy_var="first value,second value" main.dart

Output using dart and dartsjs:

my_var: first value,second value

Output using dart2native and dart compile exe:

my_var: first value

[bkonyi]

Closing this issue as --define support has been improved across all tools. Filed #44995 for the issue described by @Mabsten above.

[jodinathan]

how to add environment variables to dart run to start a VM console app?

this works: dart -Dconsole=true bin/pagebuilder_api.dart

this doesn't: dart -Dconsole=true run -Dconsole=true

[pak3nuh]

I don't think the define flag is supported across all commands evenly. I'm using dart SDK 2.19 and the test command doesn't respect the flag. For it to work, I need to run each test file individually with the run command.

Is this happening to anyone else?

[bkonyi]

@pak3nuh would you mind filing a new issue? This one has been closed for quite awhile.

[pak3nuh]

Sure. Created issue #51791