[WIP] No std #243

Restioson · 2018-05-26T12:26:27Z

Fixes #240.

TODO:

Test for whether it works in no std

Works on __my__ machine

jstnlef · 2018-05-28T17:52:10Z

pest/src/prec_climber.rs

@@ -83,7 +85,7 @@ impl<R: RuleType> BitOr for Operator<R> {
 /// [1]: https://en.wikipedia.org/wiki/Operator-precedence_parser#Precedence_climbing_method
 #[derive(Debug)]
 pub struct PrecClimber<R: RuleType> {
-    ops: HashMap<R, (u32, Assoc)>
+    ops: BTreeMap<R, (u32, Assoc)>


I'm curious about this change. It seems like this isn't relevant for no_std. Why the change?

It is relevant, HashMap isn't in alloc (it uses rand or something).

Maybe it could be cfg'd though, if it were any slower (is it? benching required)

I think that the best approach here is to limit the Vec in the contractor to 256. (assert + document with # Panics section) Then use a Box<[Assoc; 256]> to store the ops.

We'll definitely want to test to see if there's a notable difference. I suspect for most of our use-cases it'll be similar enough.

dragostis

Thanks for the PR. Things look good, however, I might have some second thoughts on the complexity that this adds.

Adding no-std is definitely a good way to move forward, however. @jstnlef what do you think about changes?

dragostis · 2018-05-30T14:29:35Z

pest/src/lib.rs

+    pub use core::*;
+    pub use core::{fmt, str};
+
+    /// Cheap-ish knockoff of std::erorr. Just does what we need it to, nothing more.


I'm wondering if this is compatible with failure. Truth be told, I guess it doesn't matter too much in the context of no-std.

Hmm... How could we test?

dragostis · 2018-05-30T14:31:14Z

derive/src/macros.rs

 macro_rules! generate_rule {
    ($name: ident, $pattern: expr) => {
        quote! {
            #[inline]
            #[allow(dead_code, non_snake_case, unused_variables)]
-            fn $name(state: Box<::pest::ParserState<Rule>>) -> ::pest::ParseResult<Box<::pest::ParserState<Rule>>> {
+            fn $name(
+                state: Box<::pest::ParserState<Rule>>


Maybe there should be a macro that returns the type here behind some cfgs in order to eliminate the duplication.

Yeah perhaps

dragostis · 2018-05-30T14:34:04Z

derive/Cargo.toml

@@ -24,3 +24,6 @@ syn = "^0.13"
 codecov = { repository = "pest-parser/pest" }
 maintenance = { status = "actively-developed" }
 travis-ci = { repository = "pest-parser/pest" }
+
+[features]
+no_std = []


What I dislike about this solution is that you need to specify no_std in both crates in that it let's the end user use an incompatible configuration (e.g., std + no-std), while providing shallow feedback. (some compile error down the line most likely) Is there any way to specify this in one single place?

Actually I probably can make them depend on eachother. I'll try that.

jstnlef · 2018-05-31T02:58:48Z

Also looks like the build is broken. Seems like some changes need to happen to pest_vm.

Restioson · 2018-05-31T05:32:51Z

Yeah, that's a bit weird. Strangely it Works On My Machine (as you can see from the screenshot), but I'll look at that soonish. Unfortunately I am writing exams right now and for the next few weeks so I may not be able to get to it that soon, but after exams I will.

wirelyre · 2018-05-31T18:19:21Z

pest/src/lib.rs

+#![cfg_attr(feature = "no_std", feature(alloc))]
+#![cfg_attr(feature = "no_std", feature(slice_concat_ext))]
+
+#![cfg(feature = "no_std")]


Looks like this exclamation mark should be removed.

wirelyre · 2018-05-31T18:20:55Z

@dragostis Does Travis need to be updated to test both regular and no_std configurations?

Restioson · 2018-05-31T19:24:55Z

@wirelyre unfortunately to get rustc to properly face the fact that there is no std you have to link it into some kind of binary, so we'd somehow need to make it do that.

dragostis · 2018-05-31T21:48:03Z

@wirelyre Yes, but that shouldn't be a huge issue. I would simply add another cargo build/cargo test run for the no_std case. This should be part of this same PR, I'd say.

@Restioson Travis issue might stem from the fact that it's running the tests on stable and you might have a different configuration.

Restioson · 2018-06-01T05:22:15Z

Probably I forgot to test it with std enabled.

Restioson · 2018-06-20T20:36:38Z

OK - I'm done exams so hopefully I'll be able to look at this soon.

sjmackenzie · 2022-06-05T10:09:16Z

How's the status of this PR? Would be fantastic to have it in.

Restioson · 2022-06-05T16:15:03Z

Hi! Unfortunately, it's been years since I've worked on this, and I imagine that both the rust no_std ecosystem as well as pest itself has evolved beyond this change. Therefore, I'll close this now as it'd probably be easier to implement this from scratch from HEAD than to update it from my 4 year old fork 😅 If someone else wants to, feel free to reuse any code from this or the approach, but personally I don't have the bandwidth to see this through right now.

Restioson added 2 commits May 23, 2018 20:59

No std for derive macro

71ed7b6

Works on __my__ machine

No std for pest crate

1b44f1f

Restioson changed the title ~~No std~~ [WIP] No std May 26, 2018

jstnlef reviewed May 28, 2018

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dragostis reviewed May 30, 2018

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wirelyre reviewed May 31, 2018

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01mf02 mentioned this pull request May 15, 2021

Make pest_generator / pest_derive no_std compatible. #513

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Restioson closed this Jun 5, 2022

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[WIP] No std #243

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[WIP] No std #243

[WIP] No std #243

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