Fix no-std compatibility and add check on CI

.circleci/config.yml

@@ -95,6 +95,9 @@ jobs:
       - run:
           name: Run all tests
           command: cargo test --all
+      - run:
+          name: Check no_std compatibility
+          command: cd no-std-check/; make setup; make all
 
   lint-rust:
     docker:

rust/Cargo.toml

@@ -3,24 +3,24 @@ name = "ics23"
 version = "0.8.0"
 authors = ["Ethan Frey <[email protected]>"]
 edition = "2021"
-exclude = ["codegen"]
+exclude = ["codegen", "no-std-check"]
 description = "Merkle proof verification library - implements Cosmos ICS23 Spec"
 repository = "https://github.com/confio/ics23/tree/master/rust"
 license = "Apache-2.0"
 rust-version = "1.56.1"
 
 [workspace]
-members = ["codegen"]
+members = ["codegen", "no-std-check"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 [dependencies]
 prost = { version = "0.11", default-features = false, features = ["prost-derive"] }
 bytes = { version = "1.0.1", default-features = false }
 hex = { version = "0.4.3", default-features = false, features = [ "alloc" ] }
 anyhow = { version = "1.0.40", default-features = false }
-sha2 = { version = "0.10.2", optional = true }
-sha3 = { version = "0.10.2", optional = true }
-ripemd = { version = "0.1.1", optional = true }
+sha2 = { version = "0.10.2", optional = true, default-features = false }
+sha3 = { version = "0.10.2", optional = true, default-features = false }
+ripemd = { version = "0.1.1", optional = true, default-features = false }
 
 [dev-dependencies]
 sha2 = { version = "0.10.2" }

rust/no-std-check/.gitignore

@@ -0,0 +1 @@
+target/

rust/no-std-check/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "no-std-check"
+version = "0.1.0"
+edition = "2021"
+resolver = "2"
+
+[dependencies]
+ics23 = { path = "../", default-features = false }
+
+[features]
+panic-handler = []

rust/no-std-check/Makefile

@@ -0,0 +1,36 @@
+NIGHTLY_VERSION=nightly
+
+.DEFAULT_GOAL := help
+
+.PHONY: all setup check-panic-conflict check-cargo-build-std check-wasm help
+
+all: ## Run all checks
+	$(MAKE) check-panic-conflict
+	$(MAKE) check-cargo-build-std
+	$(MAKE) check-wasm
+
+setup: ## Setup the required nightly toolchain and the wasm32 target
+	rustup install $(NIGHTLY_VERSION)
+	rustup target    add wasm32-unknown-unknown --toolchain $(NIGHTLY_VERSION)
+	rustup component add rust-src               --toolchain $(NIGHTLY_VERSION)
+
+check-panic-conflict: ## Check for `no_std` compliance by installing a panic handler, and any other crate importing `std` will cause a conflict. Runs on default target.
+	cargo build \
+		--no-default-features \
+		--features panic-handler
+
+check-cargo-build-std: ## Check for `no_std` compliance using Cargo nightly's `build-std` feature. Runs on the target `x86_64-unknown-linux-gnu`.
+	rustup run $(NIGHTLY_VERSION) -- \
+		cargo build -Z build-std=core,alloc \
+		--no-default-features \
+		--target x86_64-unknown-linux-gnu
+
+check-wasm: ## Check for WebAssembly and `no_std` compliance by building on the target `wasm32-unknown-unknown` and installing a panic handler.
+	rustup run $(NIGHTLY_VERSION) -- \
+		cargo build \
+		--features panic-handler \
+		--target wasm32-unknown-unknown
+
+help: ## Show this help message
+	@grep -E '^[a-z.A-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'
+

rust/no-std-check/README.md

@@ -0,0 +1,191 @@
+# `no_std` Compliance Check
+
+This crate checks the `no_std` compliance of the `ics23` crate.
+
+Based on the corresponding check in the [`ibc-rs`](https://github.com/informalsystems/ibc-rs) project.
+
+## Make Recipes
+
+- `check-panic-conflict` - Check for `no_std` compliance by installing a panic handler, and any other crate importing `std` will cause a conflict. Runs on default target.
+
+- `check-cargo-build-std` - Check for `no_std` compliance using Cargo nightly's `build-std` feature. Runs on the target `x86_64-unknown-linux-gnu`.
+
+- `check-wasm` - Check for WebAssembly and `no_std` compliance by building on the target `wasm32-unknown-unknown` and installing a panic handler.
+
+## Checking Single Unsupported Dependency
+
+By default, the check scripts try to build all unsupported dependencies and will fail. To test if a particular crate still fails the no_std check, edit the `use-unsupported` list in [Cargo.toml](./Cargo.toml) to uncomment all crates except the crate that we are interested to check. For example, to check for only the `getrandom` crate:
+
+```toml
+use-unsupported = [
+  # "tonic",
+  # "socket2",
+  "getrandom",
+  # "serde",
+  # ...,
+]
+```
+
+## Adding New Dependencies
+
+For a crate named `my-package-1.2.3`, first try and add the crate in [Cargo.toml](./Cargo.toml) of this project as:
+
+```toml
+my-package = { version = "1.2.3" }
+```
+
+Then comment out the `use-unsupported` list in the `[features]` section of Cargo.toml and replace it with an empty list temporarily for testing:
+
+```toml
+[features]
+...
+use-unsupported = []
+# use-unsupported = [
+#   "tonic",
+#   "socket2",
+#   "getrandom",
+#   ...
+# ]
+```
+
+Then import the package in [src/lib.rs](./src/lib.rs):
+
+```rust
+use my_package
+```
+
+Note that you must import the package in `lib.rs`, otherwise Cargo will skip linking the crate and fail to check for the panic handler conflicts.
+
+Then run all of the check scripts and see if any of them fails. If the check script fails, try and disable the default features and run the checks again:
+
+```rust
+my-package = { version = "1.2.3", default-features = false }
+```
+
+You may also need other tweaks such as enable custom features to make it run on Wasm.
+At this point if the checks pass, we have verified the no_std compliance of `my-package`. Restore the original `use-unsupported` list and commit the code.
+
+Otherwise if it fails, we have found a dependency that does not support `no_std`. Update Cargo.toml to make the crate optional:
+
+```rust
+my-package = { version = "1.2.3", optional = true, default-features = false }
+```
+
+Now we have to modify [lib.rs](./src/lib.rs) again and only import the crate if it is enabled:
+
+```rust
+#[cfg(feature = "my-package")]
+use my_package;
+```
+
+Retore the original `use-unsupported` list, and add `my-package` to the end of the list:
+
+```toml
+use-unsupported = [
+  "tonic",
+  "socket2",
+  "getrandom",
+  ...,
+  "my-package",
+]
+```
+
+Commit the changes so that we will track if newer version of the crate would support no_std in the future.
+
+## Conflict Detection Methods
+
+There are two methods that we use to detect `std` conflict:
+
+### Panic Handler Conflict
+
+This follows the outline of the guide by
+[Danilo Bargen](https://blog.dbrgn.ch/2019/12/24/testing-for-no-std-compatibility/)
+to register a panic handler in the `no-std-check` crate.
+Any crate imported `no-std-check` that uses `std` will cause a compile error that
+looks like follows:
+
+```
+$ cargo build
+    Updating crates.io index
+   Compiling no-std-check v0.1.0 (/data/development/informal/ibc-rs/no-std-check)
+error[E0152]: found duplicate lang item `panic_impl`
+  --> src/lib.rs:31:1
+   |
+31 | fn panic(_info: &PanicInfo) -> ! {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: the lang item is first defined in crate `std` (which `prost` depends on)
+   = note: first definition in `std` loaded from /home/ubuntu/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-b6b48477bfa8c673.rlib
+   = note: second definition in the local crate (`no_std_check`)
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0152`.
+error: could not compile `no-std-check`
+```
+
+- Pros:
+  - Can be tested using Rust stable.
+- Cons:
+  - Crates must be listed on both `Cargo.toml` and `lib.rs`.
+  - Crates that are listed in `Cargo.toml` but not imported inside `lib.rs` are not checked.
+
+### Overrride std crates using Cargo Nightly
+
+This uses the unstable `build-std` feature provided by
+[Cargo Nightly](https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#build-std).
+With this we can explicitly pass the std crates we want to support, `core` and `alloc`,
+via command line, and exclude the `std` crate.
+
+If any of the dependency uses `std`, they will fail to compile at all, albeit with
+confusing error messages:
+
+```
+$ rustup run nightly -- cargo build -j1 -Z build-std=core,alloc --target x86_64-unknown-linux-gnu
+   ...
+   Compiling bytes v1.0.1
+error[E0773]: attempted to define built-in macro more than once
+    --> /home/ubuntu/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/macros/mod.rs:1201:5
+     |
+1201 | /     macro_rules! cfg {
+1202 | |         ($($cfg:tt)*) => {
+1203 | |             /* compiler built-in */
+1204 | |         };
+1205 | |     }
+     | |_____^
+     |
+note: previously defined here
+    --> /home/ubuntu/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/macros/mod.rs:1201:5
+     |
+1201 | /     macro_rules! cfg {
+1202 | |         ($($cfg:tt)*) => {
+1203 | |             /* compiler built-in */
+1204 | |         };
+1205 | |     }
+     | |_____^
+
+error: duplicate lang item in crate `core` (which `std` depends on): `bool`.
+  |
+  = note: the lang item is first defined in crate `core` (which `bytes` depends on)
+  = note: first definition in `core` loaded from /data/development/informal/ibc-rs/no-std-check/target/x86_64-unknown-linux-gnu/debug/deps/libcore-c00d94870d25cd7e.rmeta
+  = note: second definition in `core` loaded from /home/ubuntu/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-9924c22ae1efcf66.rlib
+
+error: duplicate lang item in crate `core` (which `std` depends on): `char`.
+  |
+  = note: the lang item is first defined in crate `core` (which `bytes` depends on)
+  = note: first definition in `core` loaded from /data/development/informal/ibc-rs/no-std-check/target/x86_64-unknown-linux-gnu/debug/deps/libcore-c00d94870d25cd7e.rmeta
+  = note: second definition in `core` loaded from /home/ubuntu/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-9924c22ae1efcf66.rlib
+...
+```
+
+The above error are shown when building the `bytes` crate. This is caused by `bytes` using imports from `std`,
+which causes `std` to be included and produce conflicts with the `core` crate that is explicitly built by Cargo.
+This produces very long error messages, so we may want to use tools like `less` to scroll through the errors.
+
+Pros:
+  - Directly identify use of `std` in dependencies.
+  - Error is raised on the first dependency that imports `std`.
+
+Cons:
+  - Nightly-only feature that is subject to change.
+  - Confusing and long error messages.

rust/no-std-check/src/lib.rs

@@ -0,0 +1,36 @@
+// ensure_no_std/src/main.rs
+#![no_std]
+#![allow(unused_imports)]
+
+extern crate alloc;
+
+// Import the crates that we want to check if they are fully no-std compliance
+
+use ics23;
+
+use core::panic::PanicInfo;
+
+/*
+
+This function definition checks for the compliance of no-std in
+dependencies by causing a compile error if  this crate is
+linked with `std`. When that happens, you should see error messages
+such as follows:
+
+```
+error[E0152]: found duplicate lang item `panic_impl`
+  --> no-std-check/src/lib.rs
+   |
+12 | fn panic(_info: &PanicInfo) -> ! {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: the lang item is first defined in crate `std` (which `offending-crate` depends on)
+```
+
+ */
+#[cfg(feature = "panic-handler")]
+#[panic_handler]
+#[no_mangle]
+fn panic(_info: &PanicInfo) -> ! {
+    loop {}
+}