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Fix hygiene issues in `declare_program!` and `declare_loader!` 

The `declare_program!` and `declare_loader!` macros both expand to
new macro definitions (based on the `$name` argument). These 'inner'
macros make use of the special `$crate` metavariable to access items in
the crate where the 'inner' macros is defined.

However, this only works due to a bug in rustc. When a macro is
expanded, all `$crate` tokens in its output are 'marked' as being
resolved in the defining crate of that macro. An inner macro (including
the body of its arms) is 'just' another set of tokens that appears in
the body of the outer macro, so any `$crate` identifiers used there are
resolved relative to the 'outer' macro.

For example, consider the following code:

```rust
macro_rules! outer {
    () => {
        macro_rules! inner {
            () => {
                $crate::Foo
            }
        }
    }
}
```

The path `$crate::Foo` will be resolved relative to the crate that defines `outer`,
**not** the crate which defines `inner`.

However, rustc currently loses this extra resolution information
(referred to as 'hygiene' information) when a crate is serialized.
In the above example, this means that the macro `inner` (which gets
defined in whatever crate invokes `outer!`) will behave differently
depending on which crate it is invoked from:

When `inner` is invoked from the same crate in which it is defined,
the hygiene information will still be available,
which will cause `$crate::Foo` to be resolved in the crate which defines 'outer'.

When `inner` is invoked from a different crate, it will be loaded from
the metadata of the crate which defines 'inner'. Since the hygiene
information is currently lost, rust will 'forget' that `$crate::Foo` is
supposed to be resolved in the context of 'outer'. Instead, it will be
resolved relative to the crate which defines 'inner', which can cause
incorrect code to compile.

This bug will soon be fixed in rust (see https://github.com/rust-lang/rust/pull/72121),
which will break `declare_program!` and `declare_loader!`. Fortunately,
it's possible to obtain the desired behavior (`$crate` resolving in the
context of the 'inner' macro) by use of a procedural macro.

This commit adds a `respan!` proc-macro to the `sdk/macro` crate.
Using the newly-stabilized (on Nightly) `Span::resolved_at` method,
the `$crate` identifier can be made to be resolved in the context of the
proper crate.

Since `Span::resolved_at` is only stable on the latest nightly,
referencing it on an earlier version of Rust will cause a compilation error.
This requires the `rustversion` crate to be used, which allows conditionally
compiling code epending on the Rust compiler version in use. Since this method is already
stabilized in the latest nightly, there will never be a situation where
the hygiene bug is fixed (e.g. https://github.com/rust-lang/rust/pull/72121)
is merged but we are unable to call `Span::resolved_at`.
This commit is contained in:
Aaron Hill 2020-06-20 01:42:11 -04:00 committed by Michael Vines
parent 0b919f095d
commit 05445c718e
8 changed files with 155 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
Cargo.lock generated
View File

@ -3253,6 +3253,17 @@ dependencies = [
"webpki",
]
[[package]]
name = "rustversion"
version = "1.0.3"
source = "registry+https://github.com/rust-lang/crates.io-index"
checksum = "b9bdc5e856e51e685846fb6c13a1f5e5432946c2c90501bdc76a1319f19e29da"
dependencies = [
"proc-macro2 1.0.17",
"quote 1.0.6",
"syn 1.0.27",
]
[[package]]
name = "rusty-fork"
version = "0.2.2"
@ -3775,6 +3786,7 @@ dependencies = [
"num-derive 0.3.0",
"num-traits",
"rand 0.7.3",
"rustversion",
"solana-runtime",
"solana-sdk 1.3.0",
"solana_rbpf",
@ -4642,6 +4654,7 @@ dependencies = [
"rand 0.7.3",
"rand_chacha 0.2.2",
"rustc_version",
"rustversion",
"serde",
"serde_bytes",
"serde_derive",
@ -4674,6 +4687,7 @@ dependencies = [
"bs58 0.3.1",
"proc-macro2 1.0.17",
"quote 1.0.6",
"rustversion",
"syn 1.0.27",
]

1
programs/bpf_loader/Cargo.toml
View File

@ -21,6 +21,7 @@ thiserror = "1.0"
[dev-dependencies]
rand = "0.7.3"
rustversion = "1.0.3"
[lib]
crate-type = ["lib", "cdylib"]

8
programs/bpf_loader/src/lib.rs
View File

@ -340,6 +340,14 @@ mod tests {
}
}
#[rustversion::since(1.46.0)]
#[test]
fn test_bpf_loader_same_crate() {
// Ensure that we can invoke this macro from the same crate
// where it is defined.
solana_bpf_loader_program!();
}
#[test]
#[should_panic(expected = "ExceededMaxInstructions(10)")]
fn test_bpf_loader_non_terminating_program() {

1
sdk/Cargo.toml
View File

@ -55,6 +55,7 @@ solana-crate-features = { path = "../crate-features", version = "1.3.0", optiona
solana-logger = { path = "../logger", version = "1.3.0", optional = true }
solana-sdk-macro = { path = "macro", version = "1.3.0" }
solana-sdk-macro-frozen-abi = { path = "macro-frozen-abi", version = "1.3.0" }
rustversion = "1.0.3"
[dev-dependencies]
tiny-bip39 = "0.7.0"

1
sdk/macro/Cargo.toml
View File

@ -16,6 +16,7 @@ bs58 = "0.3.0"
proc-macro2 = "1.0"
quote = "1.0"
syn = { version = "1.0", features = ["full", "extra-traits"] }
rustversion = "1.0.3"
[package.metadata.docs.rs]
targets = ["x86_64-unknown-linux-gnu"]

73
sdk/macro/src/lib.rs
View File

@ -5,7 +5,7 @@
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::Span;
use proc_macro2::{Delimiter, Span, TokenTree};
use quote::{quote, ToTokens};
use std::convert::TryFrom;
use syn::{
@ -14,7 +14,7 @@ use syn::{
parse_macro_input,
punctuated::Punctuated,
token::Bracket,
Expr, Ident, LitByte, LitStr, Token,
Expr, Ident, LitByte, LitStr, Path, Token,
};
struct Id(proc_macro2::TokenStream);
@ -63,6 +63,75 @@ impl ToTokens for Id {
}
}
#[allow(dead_code)] // `respan` may be compiled out
struct RespanInput {
to_respan: Path,
respan_using: Span,
}
impl Parse for RespanInput {
fn parse(input: ParseStream) -> Result<Self> {
let to_respan: Path = input.parse()?;
let _comma: Token![,] = input.parse()?;
let respan_tree: TokenTree = input.parse()?;
match respan_tree {
TokenTree::Group(g) if g.delimiter() == Delimiter::None => {
let ident: Ident = syn::parse2(g.stream())?;
Ok(RespanInput {
to_respan,
respan_using: ident.span(),
})
}
val @ _ => Err(syn::Error::new_spanned(
val,
"expected None-delimited group",
)),
}
}
}
/// A proc-macro which respans the tokens in its first argument (a `Path`)
/// to be resolved at the tokens of its second argument.
/// For internal use only.
///
/// There must be exactly one comma in the input,
/// which is used to separate the two arguments.
/// The second argument should be exactly one token.
///
/// For example, `respan!($crate::foo, with_span)`
/// produces the tokens `$crate::foo`, but resolved
/// at the span of `with_span`.
///
/// The input to this function should be very short -
/// its only purpose is to override the span of a token
/// sequence containing `$crate`. For all other purposes,
/// a more general proc-macro should be used.
#[rustversion::since(1.46.0)] // `Span::resolved_at` is stable in 1.46.0 and above
#[proc_macro]
pub fn respan(input: TokenStream) -> TokenStream {
// Obtain the `Path` we are going to respan, and the ident
// whose span we will be using.
let RespanInput {
to_respan,
respan_using,
} = parse_macro_input!(input as RespanInput);
// Respan all of the tokens in the `Path`
let to_respan: proc_macro2::TokenStream = to_respan
.into_token_stream()
.into_iter()
.map(|mut t| {
// Combine the location of the token with the resolution behavior of `respan_using`
// Note: `proc_macro2::Span::resolved_at` is currently gated with cfg(procmacro2_semver_exempt)
// Once this gate is removed, we will no longer need to use 'unwrap()' to call
// the underling `proc_macro::Span::resolved_at` method.
let new_span: Span = t.span().unwrap().resolved_at(respan_using.unwrap()).into();
t.set_span(new_span);
t
})
.collect();
return TokenStream::from(to_respan);
}
#[proc_macro]
pub fn declare_id(input: TokenStream) -> TokenStream {
let id = parse_macro_input!(input as Id);

70
sdk/src/entrypoint_native.rs
View File

@ -30,6 +30,60 @@ pub type LoaderEntrypoint = unsafe extern "C" fn(
invoke_context: &dyn InvokeContext,
) -> Result<(), InstructionError>;
#[rustversion::since(1.46.0)]
#[macro_export]
macro_rules! declare_name {
($name:ident) => {
#[macro_export]
macro_rules! $name {
() => {
// Subtle:
// The outer `declare_name!` macro may be expanded in another
// crate, causing the macro `$name!` to be defined in that
// crate. We want to emit a call to `$crate::id()`, and have
// `$crate` be resolved in the crate where `$name!` gets defined,
// *not* in this crate (where `declare_name! is defined).
//
// When a macro_rules! macro gets expanded, any $crate tokens
// in its output will be 'marked' with the crate they were expanded
// from. This includes nested macros like our macro `$name` - even
// though it looks like a separate macro, Rust considers it to be
// just another part of the output of `declare_program!`.
//
// We pass `$name` as the second argument to tell `respan!` to
// apply use the `Span` of `$name` when resolving `$crate::id`.
// This causes `$crate` to behave as though it was written
// at the same location as the `$name` value passed
// to `declare_name!` (e.g. the 'foo' in
// `declare_name(foo)`
//
// See the `respan!` macro for more details.
// FIXME: Use `crate::respan!` once https://github.com/rust-lang/rust/pull/72121
// is merged.
// `respan!` respans the path `$crate::id`, which we then call (hence the extra
// parens)
(
stringify!($name).to_string(),
::solana_sdk::respan!($crate::id, $name)(),
)
};
}
};
}
#[rustversion::not(since(1.46.0))]
#[macro_export]
macro_rules! declare_name {
($name:ident) => {
#[macro_export]
macro_rules! $name {
() => {
(stringify!($name).to_string(), $crate::id())
};
}
};
}
/// Convenience macro to declare a native program
///
/// bs58_string: bs58 string representation the program's id
@ -102,13 +156,7 @@ pub type LoaderEntrypoint = unsafe extern "C" fn(
macro_rules! declare_program(
($bs58_string:expr, $name:ident, $entrypoint:expr) => (
$crate::declare_id!($bs58_string);
#[macro_export]
macro_rules! $name {
() => {
(stringify!($name).to_string(), $crate::id())
};
}
$crate::declare_name!($name);
#[no_mangle]
pub extern "C" fn $name(
@ -126,13 +174,9 @@ macro_rules! declare_program(
macro_rules! declare_loader(
($bs58_string:expr, $name:ident, $entrypoint:expr) => (
$crate::declare_id!($bs58_string);
$crate::declare_name!($name);
#[macro_export]
macro_rules! $name {
() => {
(stringify!($name).to_string(), $crate::id())
};
}
#[no_mangle]
pub extern "C" fn $name(

2
sdk/src/lib.rs
View File

@ -67,6 +67,8 @@ pub mod timing;
/// ```
pub use solana_sdk_macro::declare_id;
pub use solana_sdk_macro::pubkeys;
#[rustversion::since(1.46.0)]
pub use solana_sdk_macro::respan;
// On-chain program specific modules
pub mod account_info;