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fix(build): Meaningful compilation errors when no backend feature enabled #5767

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fix(build): Meaningful compilation errors when no backend feature enabled #5767

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6ad1a3d
fix(build): Meaningful backend compilation errors in api
theduke Sep 29, 2025
d50c7f9
Merge branch 'main' into run-745-proper-compilation-error-when-no-bac…
marxin Nov 25, 2025
2b4fe02
use declarative macro for the #[cfg] conditions
marxin Nov 25, 2025
da96336
fix build errors
marxin Nov 26, 2025
308b47b
fix docs build
marxin Nov 26, 2025
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4 changes: 2 additions & 2 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -606,10 +606,10 @@ build-capi-jsc:
build-capi-headless:
ifeq ($(CARGO_TARGET_FLAG),)
CARGO_TARGET_DIR=target/headless RUSTFLAGS="${RUSTFLAGS} -C panic=abort -C link-dead-code -C lto -O -C embed-bitcode=yes" $(CARGO_BINARY) build --target $(HOST_TARGET) --manifest-path lib/c-api/Cargo.toml --release \
--no-default-features --features compiler-headless,wasi,webc_runner --locked
--no-default-features --features compiler-headless,wasi,webc_runner,wasmer-api/cranelift --locked
else
CARGO_TARGET_DIR=target/headless RUSTFLAGS="${RUSTFLAGS} -C panic=abort -C link-dead-code -C lto -O -C embed-bitcode=yes" $(CARGO_BINARY) build $(CARGO_TARGET_FLAG) --manifest-path lib/c-api/Cargo.toml --release \
--no-default-features --features compiler-headless,wasi,webc_runner --locked
--no-default-features --features compiler-headless,wasi,webc_runner,wasmer-api/cranelift --locked
endif

build-capi-headless-ios:
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71 changes: 55 additions & 16 deletions lib/api/src/lib.rs
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Expand Up @@ -412,31 +412,70 @@
//! [`wamr`]: https://github.com/bytecodealliance/wasm-micro-runtime
//! [`wasmi`]: https://github.com/wasmi-labs/wasmi

macro_rules! cfg_compiler {
($($item:item)*) => {
$(
#[cfg(any(
feature = "cranelift",
feature = "singlepass",
feature = "llvm",
feature = "js",
feature = "jsc",
feature = "wamr",
feature = "v8",
feature = "wasmi"
))]
$item
)*
};
}

#[cfg(not(any(
feature = "sys",
feature = "js",
feature = "jsc",
feature = "singlepass",
feature = "cranelift",
feature = "llvm",
feature = "wamr",
feature = "wasmi",
feature = "v8",
feature = "wasmi"
feature = "js",
feature = "jsc"
)))]
compile_error!(
"One of: `sys`, `js`, `jsc` `wamr`, `wasmi` or `v8` features must be enabled. Please, pick one."
"wasmer requires enabling at least one backend feature: `singlepass`, `cranelift`, `llvm`, `wamr`, `wasmi`, `v8`, `js`, or `jsc`."
);

mod utils;
pub use utils::*;

mod entities;
pub use entities::memory::{MemoryView, location::MemoryLocation};
pub use entities::*;
#[cfg(all(
feature = "sys",
not(any(feature = "singlepass", feature = "cranelift", feature = "llvm"))
))]
compile_error!(
"the `sys` feature requires enabling at least one compiler backend: `singlepass`, `cranelift`, or `llvm`."
);

mod error;
pub use error::*;
cfg_compiler! {
mod utils;
pub use utils::*;
pub use entities::memory::{MemoryView, location::MemoryLocation};
mod error;
pub use error::*;
pub use entities::*;
Comment on lines +458 to +461
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Copilot AI Nov 25, 2025

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[nitpick] The cfg_compiler! macro block (lines 455-465) includes re-exports from the entities module (lines 458, 461), but the actual mod entities; declaration is located after the macro block (line 478). While both are guarded by the same feature flags, this separation makes the code harder to follow because:

  1. The re-exports appear before the module declaration
  2. The dependency on entities is not immediately visible within the macro block
  3. A reader might not realize that entities must be declared elsewhere

Consider adding a comment within the cfg_compiler! block before the entities re-exports (e.g., at line 458) noting that mod entities; is declared separately below due to the ambiguity issue mentioned in the TODO. This would help readers understand the relationship without needing to search through the file.

Copilot uses AI. Check for mistakes.
mod backend;
pub use backend::*;
mod vm;
}

mod backend;
pub use backend::*;
mod vm;
// TODO: cannot be placed into cfg_compiler due to: error: `inner` is ambiguous
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Copilot AI Nov 25, 2025

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[nitpick] The TODO comment states that mod entities; cannot be placed into cfg_compiler! due to an "inner is ambiguous" error, but doesn't provide details about what causes this ambiguity or how it might be resolved in the future.

Consider expanding this comment to explain:

  1. What specific ambiguity error occurs when placing entities in the macro
  2. What "inner" refers to (likely the inner.rs files in entity modules)
  3. Whether this is a temporary workaround or if there's a plan to restructure the module layout to avoid this issue

This will help future maintainers understand the constraint and potentially address it when refactoring.

Suggested change
// TODO: cannot be placed into cfg_compiler due to: error: `inner` is ambiguous
// NOTE: `mod entities;` cannot be placed inside `cfg_compiler!` due to a Rust compiler ambiguity error:
// When `entities` is included in the macro, the compiler reports "`inner` is ambiguous" because multiple
// submodules within `entities` (e.g., `entities/memory/inner.rs`, `entities/table/inner.rs`, etc.) have files named `inner.rs`.
// This causes the module resolution to fail, as Rust cannot disambiguate which `inner` is being referred to.
// As a workaround, `mod entities;` is declared outside the macro with explicit `#[cfg]` gating.
// If the module layout is restructured in the future (e.g., by renaming `inner.rs` files or flattening the hierarchy),
// this workaround may no longer be necessary and `mod entities;` could be moved into `cfg_compiler!`.

Copilot uses AI. Check for mistakes.
#[cfg(any(
feature = "cranelift",
feature = "singlepass",
feature = "llvm",
feature = "js",
feature = "jsc",
feature = "wamr",
feature = "v8",
feature = "wasmi"
))]
mod entities;

pub use wasmer_types::{
Bytes, CompileError, DeserializeError, ExportIndex, ExportType, ExternType, FrameInfo,
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2 changes: 1 addition & 1 deletion lib/cache/Cargo.toml
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Expand Up @@ -35,5 +35,5 @@ filesystem = []
blake3-pure = ["blake3/pure"]

[package.metadata.docs.rs]
features = ["wasmer/sys", "wasmer/compiler"]
features = ["wasmer/sys", "wasmer/compiler", "wasmer/cranelift"]
rustc-args = ["--cfg", "docsrs"]
1 change: 1 addition & 0 deletions lib/cli/Cargo.toml
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Expand Up @@ -319,3 +319,4 @@ bin-dir = "bin/{ bin }.exe"

[package.metadata.docs.rs]
rustc-args = ["--cfg", "docsrs"]
features = ["wasmer/cranelift"]
2 changes: 1 addition & 1 deletion lib/compiler/src/engine/artifact.rs
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Expand Up @@ -454,7 +454,7 @@ impl Artifact {
get_got_address(RelocationTarget::LibCall(wasmer_vm::LibCall::EHPersonality)),
)?;

#[cfg(not(target_arch = "wasm32"))]
#[cfg(all(feature = "compiler", not(target_arch = "wasm32")))]
{
engine_inner.register_perfmap(&finished_functions, module_info)?;
}
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2 changes: 1 addition & 1 deletion lib/compiler/src/engine/inner.rs
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Expand Up @@ -540,7 +540,7 @@ impl EngineInner {
.register_frame_info(frame_info);
}

#[cfg(not(target_arch = "wasm32"))]
#[cfg(all(feature = "compiler", not(target_arch = "wasm32")))]
pub(crate) fn register_perfmap(
&self,
finished_functions: &PrimaryMap<LocalFunctionIndex, FunctionExtent>,
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35 changes: 25 additions & 10 deletions lib/compiler/src/lib.rs
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Expand Up @@ -20,6 +20,18 @@
)]
#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]

macro_rules! cfg_std_or_core {
($($item:item)*) => {
$(
#[cfg(any(
feature = "std",
feature = "core",
))]
$item
)*
};
}

#[cfg(all(feature = "std", feature = "core"))]
compile_error!(
"The `std` and `core` features are both enabled, which is an error. Please enable only once."
Expand All @@ -32,6 +44,7 @@ compile_error!("Both the `std` and `core` features are disabled. Please enable o
extern crate alloc;

#[allow(unused_imports)]
#[cfg(any(feature = "std", feature = "core"))]
mod lib {
#[cfg(feature = "core")]
pub mod std {
Expand All @@ -46,20 +59,22 @@ mod lib {
}
}

mod engine;
mod traits;
cfg_std_or_core! {
mod engine;
mod traits;

pub mod misc;
pub mod object;
pub mod serialize;
pub mod types;
pub mod misc;
pub mod object;
pub mod serialize;
pub mod types;

pub use crate::engine::*;
pub use crate::traits::*;
pub use crate::engine::*;
pub use crate::traits::*;

mod artifact_builders;
mod artifact_builders;

pub use self::artifact_builders::*;
pub use self::artifact_builders::*;
}

#[cfg(feature = "compiler")]
mod compiler;
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1 change: 1 addition & 0 deletions lib/middlewares/Cargo.toml
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Expand Up @@ -31,3 +31,4 @@ maintenance = { status = "actively-developed" }

[package.metadata.docs.rs]
rustc-args = ["--cfg", "docsrs"]
features = ["wasmer/cranelift"]
2 changes: 1 addition & 1 deletion lib/swift/Cargo.toml
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Expand Up @@ -33,5 +33,5 @@ wasmer-package.workspace = true
uniffi = { version = "0.27", features = ["build"] }

[package.metadata.docs.rs]
features = ["wasmer/sys", "wasmer/compiler"]
features = ["wasmer/sys", "wasmer/cranelift"]
rustc-args = ["--cfg", "docsrs"]
1 change: 1 addition & 0 deletions lib/sys-utils/Cargo.toml
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Expand Up @@ -28,6 +28,7 @@ tracing-subscriber = { workspace = true, features = ["fmt"] }
tracing.workspace = true

[package.metadata.docs.rs]
features = ["wasmer/cranelift"]
rustc-args = ["--cfg", "docsrs"]

[features]
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2 changes: 1 addition & 1 deletion lib/wai-bindgen-wasmer/Cargo.toml
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Expand Up @@ -42,5 +42,5 @@ singlepass = ["wasmer/singlepass"]
llvm = ["wasmer/llvm"]

[package.metadata.docs.rs]
features = ["wasmer/sys", "wasmer/compiler"]
features = ["wasmer/sys", "wasmer/cranelift"]
rustc-args = ["--cfg", "docsrs"]
2 changes: 1 addition & 1 deletion lib/wasi-types/Cargo.toml
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Expand Up @@ -41,5 +41,5 @@ version = "1.3.0"
enable-serde = ["serde", "wasmer-types/serde"]

[package.metadata.docs.rs]
features = ["wasmer/sys", "wasmer/compiler"]
features = ["wasmer/sys", "wasmer/cranelift"]
rustc-args = ["--cfg", "docsrs"]
2 changes: 1 addition & 1 deletion lib/wasix/Cargo.toml
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Expand Up @@ -264,7 +264,7 @@ enable-serde = [
[package.metadata.docs.rs]
features = [
"wasmer/sys",
"wasmer/compiler",
"wasmer/cranelift",
"webc_runner_rt_wcgi",
"webc_runner_rt_dcgi",
"webc_runner_rt_dproxy",
Expand Down
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