Add (non-working) cpp-to-wasm test

ffi/capi/Cargo.toml

@@ -30,9 +30,9 @@ all-features = true
 # Omit most optional dependency features from permutation testing
 skip_optional_dependencies = true
 # Bench feature gets tested separately and is only relevant for CI.
-# wearos/freertos/x86tiny are not relevant in normal environments,
+# wearos/freertos/x86tiny/wasm_embedding are not relevant in normal environments,
 # and smaller_static gets tested on the FFI job anyway
-denylist = ["bench", "wearos", "freertos", "x86tiny", "smaller_static"]
+denylist = ["bench", "wearos", "freertos", "x86tiny", "smaller_static", "wasm_embedding"]
 
 [lib]
 crate-type = ["staticlib", "rlib", "cdylib"]
@@ -56,6 +56,9 @@ x86tiny = ["dlmalloc"]
 # Enables no_std builds for freertos
 freertos = ["freertos-rust", "cortex-m"]
 
+# Enables things that enable Rust to be linked to C++ (etc) in WASM
+wasm_embedding = []
+
 [dependencies]
 fixed_decimal = { path = "../../utils/fixed_decimal" }
 icu_decimal = { path = "../../components/decimal/" }

ffi/capi/src/wasm_glue.rs

@@ -61,3 +61,45 @@ pub unsafe extern "C" fn icu4x_init() {
         .map(|()| log::set_max_level(LevelFilter::Debug))
         .unwrap();
 }
+
+#[cfg(feature = "wasm_embedding")]
+mod allocator {
+    use alloc::alloc::GlobalAlloc;
+    use alloc::alloc::Layout;
+
+    // The default global allocator for Rust works fine when Rust
+    // is controlling the entire WASM stack, however when linked to
+    // C++ it does not, so we fall back to malloc/free
+    #[global_allocator]
+    static GLOBAL: WasmMalloc = WasmMalloc;
+
+    pub struct WasmMalloc;
+
+    extern "C" {
+        fn malloc(size: usize) -> *mut u8;
+        fn free(ptr: *mut u8);
+        fn calloc(num: usize, size: usize) -> *mut u8;
+        fn realloc(ptr: *mut u8, size: usize) -> *mut u8;
+    }
+    unsafe impl GlobalAlloc for WasmMalloc {
+        #[inline]
+        unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+            malloc(layout.size())
+        }
+
+        #[inline]
+        unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
+            free(ptr)
+        }
+
+        #[inline]
+        unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+            calloc(layout.size(), 1)
+        }
+
+        #[inline]
+        unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+            realloc(ptr, new_size)
+        }
+    }
+}

ffi/cpp/examples/fixeddecimal-wasm/.gitignore

@@ -0,0 +1 @@
+a.out

ffi/cpp/examples/fixeddecimal-wasm/Makefile

@@ -0,0 +1,25 @@
+# This file is part of ICU4X. For terms of use, please see the file
+# called LICENSE at the top level of the ICU4X source tree
+# (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+.DEFAULT_GOAL := test
+.PHONY: build
+
+ALL_HEADERS := $(wildcard ../../include/*.hpp) $(wildcard ../../../capi/include/*.h)
+ALL_RUST := $(wildcard ../../../capi//src/*.rs)
+
+$(ALL_RUST):
+
+$(ALL_HEADERS):
+
+
+
+
+../../../../target/wasm32-unknown-unknown/debug/libicu_capi.a: $(ALL_RUST)
+	cargo +nightly build -p icu_capi --target wasm32-unknown-unknown --features wasm_embedding
+
+# Currently this doesn't run successfully, however it's the status quo of compiling ICU4X in C++ to WASM
+main.html: ../../../../target/wasm32-unknown-unknown/debug/libicu_capi.a $(ALL_HEADERS) test.cpp
+	emcc -std=c++17 test.cpp ../../../../target/wasm32-unknown-unknown/debug/libicu_capi.a -ldl -lpthread -lm -g  -o main.html --emrun -sWASM=1
+
+build: main.html