Display for snapshots

[piotmag769]

Came up with it after the previous PR was closed :/

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This change is 

[piotmag769]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @orizi)

a discussion (no related file):
I added this because without it snapshot implementations of Display required specific import of the concrete impl - example below

package structure:

src/
  lib.cairo
  abc.cairo

lib.cairo:

mod abc;
use core::fmt::{Display, Formatter, Error};

#[derive(Drop)]
struct Y {}

impl DisplayY of Display<Y> {
  fn fmt(self: @Y, ref f: Formatter) -> Result<(), Error> {
      Result::Ok(())
  }
}

impl DisplayYSnap of Display<@Y> {
  fn fmt(self: @@Y, ref f: Formatter) -> Result<(), Error> {
    Result::Ok(())
  }
}

abc.cairo

use super::Y;

fn func() {
  println!("{}", @Y{});
}

For this package scarb build fails. The fix is to add use super::DisplayYSnap; to abc.cairo. Is it a desired behaviour?

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[piotmag769]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @orizi)

a discussion (no related file):

Previously, piotmag769 (Piotr Magiera) wrote…

I added this because without it snapshot implementations of Display required specific import of the concrete impl - example below

package structure:

src/
  lib.cairo
  abc.cairo

lib.cairo:

mod abc;
use core::fmt::{Display, Formatter, Error};

#[derive(Drop)]
struct Y {}

impl DisplayY of Display<Y> {
  fn fmt(self: @Y, ref f: Formatter) -> Result<(), Error> {
      Result::Ok(())
  }
}

impl DisplayYSnap of Display<@Y> {
  fn fmt(self: @@Y, ref f: Formatter) -> Result<(), Error> {
    Result::Ok(())
  }
}

abc.cairo

use super::Y;

fn func() {
  println!("{}", @Y{});
}

For this package scarb build fails. The fix is to add use super::DisplayYSnap; to abc.cairo. Is it a desired behaviour?

Clarification:
the error message is

error: Trait has no implementation in context: core::fmt::Display::<@uwu::Y>
 --> /Users/piotrmagiera/SWM/uwu/src/abc.cairo[println_macro][writeln_macro]:3:31
    match core::fmt::Display::fmt(__write_macro_arg0__, ref __formatter_for_print_macros__) {

and the part of the code

impl DisplayY of Display<Y> {
  fn fmt(self: @Y, ref f: Formatter) -> Result<(), Error> { 
    Result::Ok(()) 
  }
}

is not needed to reproduce

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[piotmag769]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @orizi)

a discussion (no related file):

Previously, piotmag769 (Piotr Magiera) wrote…

Clarification:
the error message is

error: Trait has no implementation in context: core::fmt::Display::<@uwu::Y>
 --> /Users/piotrmagiera/SWM/uwu/src/abc.cairo[println_macro][writeln_macro]:3:31
    match core::fmt::Display::fmt(__write_macro_arg0__, ref __formatter_for_print_macros__) {

and the part of the code

impl DisplayY of Display<Y> {
  fn fmt(self: @Y, ref f: Formatter) -> Result<(), Error> { 
    Result::Ok(()) 
  }
}

is not needed to reproduce

Update: same thing happens when implementing Display for Array<Y>

error: Trait has no implementation in context: core::fmt::Display::<core::array::Array::<uwu::Y>>
 --> /Users/piotrmagiera/SWM/uwu/src/abc.cairo[println_macro][writeln_macro]:3:31
    match core::fmt::Display::fmt(__write_macro_arg0__, ref __formatter_for_print_macros__) {
                              ^*^

I've used Scarb depending on Cairo from the main branch (bumped the Cairo deps for Scarb locally and built it), so it uses the latest possible compiler version - both issues still occur.

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[orizi]

Reviewable status: 0 of 1 files reviewed, 2 unresolved discussions (waiting on @piotmag769)

a discussion (no related file):
I'm not sure we actually want this - do note that any user of this can actually just call this with adding a *.
The diagnostic itself indeed should be better mapped to the original user code.

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[piotmag769]

Reviewable status: 0 of 1 files reviewed, 2 unresolved discussions (waiting on @orizi)

a discussion (no related file):

do note that any user of this can actually just call this with adding a *

Isn't Copy trait required to use desnap operator though? It would be helpful for printing e.g. snapshot of a struct that has a field of a type Array<felt252>. Note that there is a similar generic implementation for Debug for snapshots in corelib already.

cairo/corelib/src/fmt.cairo

Line 71 in 8290898

impl DebugSnapshot<T, +Debug<T>> of Debug<@T> {

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[orizi]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion

[orizi]

Reviewable status: all files reviewed, 1 unresolved discussion

a discussion (no related file):
Adding @ilyalesokhin-starkware for 2nd eye.

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[orizi]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @piotmag769)

a discussion (no related file):
@ilyalesokhin-starkware for 2nd eye

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[gilbens-starkware]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @orizi and @piotmag769)