Add Crystal.main #4998

asterite · 2017-09-17T18:25:53Z

Please read the doc comments in the commit.

As an example, to implement what is needed in #4793 one can now write:

@[Link("allegro")]
lib LibAllegro
  fun al_run_main(argc : LibC::Int, argv : LibC::Char**, user_main : (LibC::Int, LibC::Char** -> LibC::Int)) : LibC::Int
end

# Redefine main function
fun main(argc : Int32, argv : UInt8**) : Int32
  # Pass Crystal's main function as a callback
  LibAllegro.al_run_main(argc, argv, ->Crystal.main)
end

This is a breaking change because the macro redefine_main is removed.

One more thing: I expose main to Crystal as __crystal_c_main. This makes it possible to have a user-defined method named main, so kinda fixes what's described in #4761. Next, the compiler should disallow funs and methods with the same names, but I'll send that in a separate PR.

^ I decided it's better for now to expose it as main, because otherwise to redefine it one would need to use the same cryptic name. I'll later change the compiler to never expose fun main to Crystal code because it never needs to be invoked.

There's one TODO there that is fixed by the first commit in this PR. We can get rid of it after releasing the next version.

I also removed the single usage of redefine_main, which maybe was needed before, but removing it I got the SDL samples to work (they didn't work anymore).

This makes it possible to invoke `__crystal_main` from inside types and modules.

Sija · 2017-09-17T18:34:26Z

src/crystal/main.cr

+  # - Invokes the given *block*
+  # - Handles unhandled exceptions
+  # - Invokes `at_exit` handlers
+  # - Flushes STDOUT and STDERR


Please, enclose STDOUT and STDERR in backticks `` to link 'em to docs.

Sija · 2017-09-17T18:38:12Z

src/crystal/main.cr

+  end
+
+  # Executes the main user code. This normally is executed
+  # after initializing the GC and executing `at_exit` handlers.


[...] and before executing at_exit handlers.

?

Sija · 2017-09-18T00:50:05Z

src/crystal/main.cr

+  # in Crystal (like `new` for classes) can be used.
+  def self.main(argc : Int32, argv : UInt8**)
+    main do
+      _crystal_main(argc, argv)


Shouldn't be here main_user_code(argc, argv) instead?

This makes it simpler to redefine main with custom logic.

ysbaddaden · 2017-09-18T16:40:46Z

Looks great!

One minor thing: sometimes we don't want a main, for example Android applications are shared objects, loaded from Java (JNI).

asterite · 2017-09-18T17:08:20Z

@ysbaddaden Was that possible before this PR?

RX14 · 2017-09-18T22:57:01Z

src/crystal/main.cr

+  # Executes the main user code. This normally is executed
+  # after initializing the GC and before executing `at_exit` handlers.
+  #
+  # You should never invoke this method unless you need to


Would it be possible to raise early if this is executed twice? Seems like a bit of an edge case but might be worth protecting. This could be another PR though.

Sija · 2017-09-19T13:26:10Z

src/crystal/main.cr

+  #
+  # ```
+  # fun main(argc : Int32, argv : UInt8**) : Int32
+  #   LibFoo.init_foo_and_invoke_main(argc, argv, ->Crystal.main)


Shouldn't ->Crystal.main be ->Crystal.main(Int32, UInt8**)?

If it's a lib call the compiler figures out the argument types.

Didn't know that, cushtie!

ysbaddaden · 2017-09-19T13:30:22Z

@asterite no, it wasn't possible, but since it's touching main declarations, it could have been an opportunity to allow to skip generating a default main function. Anyway, no big deal.

david50407 · 2017-09-19T14:49:59Z

Can we also provide Crystal.main(argc : Int32, argv : UInt8**, envp : UInt8**) in this change?
envp is used in many C programs, maybe we can allow this argument and skip it first.

MSDN page for envp: https://msdn.microsoft.com/en-us/library/k104fy6h.aspx

Sija · 2017-09-19T15:00:12Z

@david50407 envp parameter is widely accepted, yet not standardised, see discussion on SO. btw, wouldn't it be redundant with access to ENV?

Fryguy · 2017-09-25T19:57:52Z

@asterite This is awesome, and is exactly what I was trying to accomplish myself, but couldn't figure out. This is really nice!

Codegen: always expose __crystal_main

968e640

This makes it possible to invoke `__crystal_main` from inside types and modules.

asterite added breaking-change kind:feature kind:refactor topic:stdlib labels Sep 17, 2017

asterite self-assigned this Sep 17, 2017

Sija reviewed Sep 17, 2017

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Sija reviewed Sep 18, 2017

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Add Crystal.main

5f0fe1c

This makes it simpler to redefine main with custom logic.

RX14 reviewed Sep 18, 2017

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RX14 approved these changes Sep 18, 2017

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bcardiff approved these changes Sep 19, 2017

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asterite merged commit c81b81d into crystal-lang:master Sep 19, 2017

Sija reviewed Sep 19, 2017

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Sija mentioned this pull request Sep 21, 2017

Expose alt_name for redefine_main #4798

Closed

mverzilli added this to the Next milestone Sep 22, 2017

mvz mentioned this pull request Apr 9, 2018

Fix autorun jhass/crystal-gobject#17

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Add Crystal.main #4998

Add Crystal.main #4998

asterite commented Sep 17, 2017 •

edited

Sija Sep 17, 2017

Sija Sep 17, 2017

Sija Sep 18, 2017

ysbaddaden commented Sep 18, 2017

asterite commented Sep 18, 2017

RX14 Sep 18, 2017

Sija Sep 19, 2017

asterite Sep 19, 2017

Sija Sep 19, 2017

ysbaddaden commented Sep 19, 2017

david50407 commented Sep 19, 2017

Sija commented Sep 19, 2017

Fryguy commented Sep 25, 2017

Add Crystal.main #4998

Add Crystal.main #4998

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asterite commented Sep 17, 2017 • edited

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ysbaddaden commented Sep 19, 2017

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Sija commented Sep 19, 2017

Fryguy commented Sep 25, 2017

asterite commented Sep 17, 2017 •

edited