DART_VM_OPTIONS for self-executables not working!

[gmpassos]

As mentioned on README, Dart 3.4.0 supports DART_VM_OPTIONS for self-executables:

README.md:

...
### Dart Runtime

- Dart VM flags and options can now be provided to any executable generated
  using `dart compile exe` via the `DART_VM_OPTIONS` environment variable.
  `DART_VM_OPTIONS` should be set to a list of comma-separated flags and options
  with no whitespace. Options that allow for multiple values to be provided as
  comma-separated values are not supported (e.g.,
  `--timeline-streams=Dart,GC,Compiler`).

  Example of a valid `DART_VM_OPTIONS` environment variable:

   DART_VM_OPTIONS=--random_seed=42,--verbose_gc

...

---

Example:

foo.dart:

void main(List<String> args) {
  print("FOO>> args: $args");
}

run-foo.sh:

#!/bin/bash

dart compile exe foo.dart

export DART_VM_OPTIONS=--random_seed=42,--verbose_gc
echo "DART_VM_OPTIONS: $DART_VM_OPTIONS"

echo "Running executable:"
./foo.exe

Output of ./run-foo.sh:

Generated: /private/tmp/dart-test-foo/foo.exe
DART_VM_OPTIONS: --random_seed=42,--verbose_gc
Running executable:
Usage: dart [<vm-flags>] <dart-script-file> [<script-arguments>]

Executes the Dart script <dart-script-file> with the given list of <script-arguments>.

Common VM flags:
--help or -h
  Display this message (add -v or --verbose for information about
  all VM options).
--packages=<path>
  Where to find a package spec file.
--define=<key>=<value> or -D<key>=<value>
  Define an environment declaration. To specify multiple declarations,
  use multiple instances of this option.
--snapshot-kind=<snapshot_kind>
--snapshot=<file_name>
  These snapshot options are used to generate a snapshot of the loaded
  Dart script:
    <snapshot-kind> controls the kind of snapshot, it could be
                    kernel(default) or app-jit
    <file_name> specifies the file into which the snapshot is written
--version
  Print the SDK version.

For some reason it's always showing the dart CLI help message.

---

dart --version:

Dart SDK version: 3.4.0 (stable) (Mon May 6 07:59:58 2024 -0700) on "macos_x64"

---

[gmpassos]

FYI: @bkonyi

[bkonyi]

Thanks for the heads up @gmpassos. I'm able to reproduce and it looks like there was some oversights in the implementation that wasn't caught by testing. I have a fix up for review here.

[gmpassos]

... I have a fix up for review here.

Please add documentation for DART_VM_OPTIONS, especially for self-executables. This is not documented anywhere.

[bkonyi]

Cherrypick request has been filed here: #55818.

[bkonyi]

Please add documentation for DART_VM_OPTIONS, especially for self-executables. This is not documented anywhere.

There's not any obvious spot to put this on the website since it's relatively niche functionality, but I've added documentation in the SDK that should make this a bit easier to discover: https://dart-review.googlesource.com/c/sdk/+/367800

[gmpassos]

... it's relatively niche functionality.

The default max heap size is 30GB:

sdk/runtime/vm/globals.h

Line 62 in f4cc1eb

const intptr_t kDefaultMaxOldGenHeapSize = (kWordSize <= 4) ? 1536 : 30720;

IMHO, every self-executable in production should define its memory limit, since running any application with a heap limit higher than the available memory is a recipe for disaster. Since the only way to define the max heap size in a self-executable is by using DART_VM_OPTIONS, this shouldn't be treated as a hidden property.