Fix handling of C standard support for Emscripten.
Emscripten version numbers are unrelated to Clang version numbers,
so it is necessary to change the version checks for `c_std=c17` & co.
Without that, no project that defaults to C17 or newer will build with
Emscripten.
See https://github.com/pyodide/pyodide/discussions/4762 for more
context. Also note that this bug caused defaulting to C17 in
scikit-learn to be reverted (scikit-learn#29015), and it may be a
problem for SciPy 1.14.0 too since that release will upgrade from C99
to C17.
Co-authored-by: Loic Esteve <loic.esteve@ymail.com>
diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index 7e21461..18b25d4 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -201,6 +201,16 @@
id = 'emscripten'
+ # Emscripten uses different version numbers than Clang; `emcc -v` will show
+ # the Clang version number used as well (but `emcc --version` does not).
+ # See https://github.com/pyodide/pyodide/discussions/4762 for more on
+ # emcc <--> clang versions. Note that c17/c18/c2x are always available, since
+ # the lowest supported Emscripten version used a new-enough Clang version.
+ _C17_VERSION = '>=1.38.35'
+ _C18_VERSION = '>=1.38.35'
+ _C2X_VERSION = '>=1.38.35' # 1.38.35 used Clang 9.0.0
+ _C23_VERSION = '>=3.0.0' # 3.0.0 used Clang 18.0.0
+
def __init__(self, ccache: T.List[str], exelist: T.List[str], version: str, for_machine: MachineChoice, is_cross: bool,
info: 'MachineInfo',
linker: T.Optional['DynamicLinker'] = None,
diff --git a/test cases/wasm/1 basic/meson.build b/test cases/wasm/1 basic/meson.build
index 1092a9b..d275992 100644
--- a/test cases/wasm/1 basic/meson.build
+++ b/test cases/wasm/1 basic/meson.build
@@ -1,4 +1,9 @@
-project('emcctest', 'c', 'cpp')
+project('emcctest', 'c', 'cpp',
+ default_options: [
+ 'c_std=c17',
+ 'cpp_std=c++17',
+ ]
+)
executable('hello-c', 'hello.c')
executable('hello', 'hello.cpp')
