"pub run" should spawn an isolate rather than starting a subprocess

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="96" height="96"hspace="10"> Issue by nex3
Originally opened as dart-lang/sdk#21821

---

Currently "pub run" starts a subprocess to run its code. It should instead spawn an isolate to avoid VM startup time and provide accurate information for the stdioType getter.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

---

Added Pub-Run label.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

---

This is blocking dart-lang/test#19.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="48" height="48"hspace="10"> Comment by seaneagan

---

In the meantime could pub run temporarily set an environment variable in the sub-process for us to check the stdioType e.g. PUB_RUN_STDIOTYPE?

This is also blocking https://github.com/google/stagehand/issues/147

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="48" height="48"hspace="10"> Comment by seaneagan

---

This would fix stdioType, but wouldn't it break Platform.script?

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

---

Platform.script is already not what people expect under "pub run". Ideally there would be a way to spawn an isolate with a custom value for Platform.script, but that feature request is out-of-scope for this issue.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="48" height="48"hspace="10"> Comment by seaneagan

---

I think Platform.script currently references the pub cache location of the script, no? I only need basenameWithoutExtension(Platform.script), so that has been sufficient for my needs, and I'm not sure what a better value would be. But I would no longer have that if the isolate retains the Platform.script of pub itself, rather than of the spawned script.

(BTW my use case is for unscripted to determine the command name for help text output.)

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="48" height="48"hspace="10"> Comment by seaneagan

---

See also issue #1234, which would be an even better solution for my use case.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/188?v=3" align="left" width="48" height="48"hspace="10"> Comment by nex3

---

This is also blocking dart-lang/test#86.

[DartBot]

This comment was originally written by emil.n.pe...@gmail.com

---

Case where this is a real problem:
"stdout.terminalColumns" throws when file is run with "pub run" rather than "dart"