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Migrate back to std:: stylistically (#554)

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* Migrate back to `std::` stylistically

This commit moves away from idioms such as `alloc::` and `core::` as
imports of standard data structures and types. Instead it migrates all
crates to uniformly use `std::` for importing standard data structures
and types. This also removes the `std` and `core` features from all
crates to and removes any conditional checking for `feature = "std"`

All of this support was previously added in #407 in an effort to make
wasmtime/cranelift "`no_std` compatible". Unfortunately though this
change comes at a cost:

* The usage of `alloc` and `core` isn't idiomatic. Especially trying to
  dual between types like `HashMap` from `std` as well as from
  `hashbrown` causes imports to be surprising in some cases.
* Unfortunately there was no CI check that crates were `no_std`, so none
  of them actually were. Many crates still imported from `std` or
  depended on crates that used `std`.

It's important to note, however, that **this does not mean that wasmtime
will not run in embedded environments**. The style of the code today and
idioms aren't ready in Rust to support this degree of multiplexing and
makes it somewhat difficult to keep up with the style of `wasmtime`.
Instead it's intended that embedded runtime support will be added as
necessary. Currently only `std` is necessary to build `wasmtime`, and
platforms that natively need to execute `wasmtime` will need to use a
Rust target that supports `std`. Note though that not all of `std` needs
to be supported, but instead much of it could be configured off to
return errors, and `wasmtime` would be configured to gracefully handle
errors.

The goal of this PR is to move `wasmtime` back to idiomatic usage of
features/`std`/imports/etc and help development in the short-term.
Long-term when platform concerns arise (if any) they can be addressed by
moving back to `no_std` crates (but fixing the issues mentioned above)
or ensuring that the target in Rust has `std` available.

* Start filling out platform support doc
This commit is contained in:
Alex Crichton
2019-11-19 00:04:06 -06:00
committed by Dan Gohman
parent c423a1c2f0
commit 39e57e3e9a
99 changed files with 271 additions and 444 deletions
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8
crates/debug/Cargo.toml
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@@ -18,17 +18,11 @@ cranelift-codegen = { version = "0.50.0", features = ["enable-serde"] }
cranelift-entity = { version = "0.50.0", features = ["enable-serde"] }
cranelift-wasm = { version = "0.50.0", features = ["enable-serde"] }
faerie = "0.13.0"
wasmtime-environ = { path = "../environ", default-features = false }
wasmtime-environ = { path = "../environ" }
target-lexicon = { version = "0.9.0", default-features = false }
anyhow = "1.0"
hashbrown = { version = "0.6.0", optional = true }
thiserror = "1.0.4"
more-asserts = "0.2.1"
[features]
default = ["std"]
std = ["cranelift-codegen/std", "cranelift-wasm/std", "wasmtime-environ/std"]
core = ["hashbrown/nightly", "cranelift-codegen/core", "cranelift-wasm/core"]
[badges]
maintenance = { status = "actively-developed" }