build runner and build daemon do not emit warnings from the build

[annagrin]

I tried to write a test for properly handling the --enable-experiment option in build daemon and discovered that warnings are not emitted from the compiler. Same for build runner.

See: #3183
In particular, discussion in the comments: https://github.com/dart-lang/build/pull/3183/files/286019b0881bf346af7d2278d46a1e7a69e3f99d#diff-52928f64ac1f76149efee2f7237ff7a360edd69263873a733902b7f701a8abac

As a note, the argument is passed to the build - compiling code that uses constructor tearoffs and using build runner with --enable-experiment=constructor-tearoffs succeeds, while using build runner with --enable-experiment=constructor-tearoff fails to compile, as expected.

Repro: try to build a simple app with one file using a non-existing flag: --enable-experiments=constructor-tearoff.

Dartdevc emits the warning:

➜  dartdevc --enable-experiment=constructor-tearoff web/main.dart -o output.js
Unknown experiment: constructor-tearoff

build_runner does not emit the warning:

➜  dart run build_runner build --enable-experiment=constructor-tearoff --verbose
[INFO] Entrypoint:Generating build script...
[INFO] Entrypoint:Generating build script completed, took 405ms

[INFO] Bootstrap:Precompiling build script......
[INFO] Bootstrap:Precompiling build script... completed, took 6.5s

[FINE] Bootstrap:Core package locations file does not exist
[INFO] BuildDefinition:Initializing inputs
[INFO] BuildDefinition:Building new asset graph...
[INFO] BuildDefinition:Building new asset graph completed, took 911ms

[INFO] BuildDefinition:Checking for unexpected pre-existing outputs....
[INFO] BuildDefinition:Checking for unexpected pre-existing outputs. completed, took 1ms

[INFO] Build:Running build...
[INFO] build_resolvers:Generating SDK summary...
[INFO] Heartbeat:3.2s elapsed, 0/1 actions completed.
[INFO] build_resolvers:Generating SDK summary completed, took 3.1s

[INFO] Heartbeat:4.3s elapsed, 0/2 actions completed.
[INFO] Heartbeat:5.3s elapsed, 0/2 actions completed.
[INFO] Build:Running build completed, took 6.3s

[INFO] Build:Caching finalized dependency graph...
[INFO] Build:Caching finalized dependency graph completed, took 181ms

[INFO] Build:Succeeded after 6.4s with 14 outputs (1315 actions)

[jakemac53]

@annagrin do you know if this is still an issue? Is it worth fixing?

[github-actions]

Without additional information we're not able to resolve this issue. Feel free to add more info or respond to any questions above and we can reopen the case. Thanks for your contribution!