compilers/linkers: Add a representation for wasm-ld

Emscripten does have a stand alone linker, wasm-ld. This patch adds the
linker, adds detection for the linker, and removes the IsLinkerMixin for
emscripten. This is a little more correct, and makes the code a lot
cleaner and more robust.

docs/markdown/Reference-tables.md

@@ -37,10 +37,11 @@ These are return values of the `get_linker_id` method in a compiler object.
 
 | Value      | Linker family                               |
 | -----      | ---------------                             |
-| ld.bfd     | The GNU linker                              | 
+| ld.bfd     | The GNU linker                              |
 | ld.gold    | The GNU gold linker                         |
 | ld.lld     | The LLVM linker, with the GNU interface     |
 | ld.solaris | Solaris and illumos                         |
+| ld.wasm    | emscripten's wasm-ld linker                 |
 | ld64       | Apple ld64                                  |
 | link       | MSVC linker                                 |
 | lld-link   | The LLVM linker, with the MSVC interface    |

docs/markdown/snippets/wasm_ld.md

@@ -0,0 +1,5 @@
+## Property support emscripten's wasm-ld
+
+Before 0.54.0 we treated emscripten as both compiler and linker, which isn't
+really true. It does have a linker, called wasm-ld (meson's name is ld.wasm).
+This is a special version of clang's lld. This will now be detected properly.

mesonbuild/compilers/c.py

@@ -27,7 +27,7 @@ from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler
 from .mixins.elbrus import ElbrusCompiler
 from .mixins.pgi import PGICompiler
-from .mixins.islinker import BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin
+from .mixins.islinker import LinkerEnvVarsMixin
 from .mixins.emscripten import EmscriptenMixin
 from .compilers import (
     gnu_winlibs,
@@ -133,7 +133,7 @@ class AppleClangCCompiler(ClangCCompiler):
     _C18_VERSION = '>=11.0.0'
 
 
-class EmscriptenCCompiler(EmscriptenMixin, BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, ClangCCompiler):
+class EmscriptenCCompiler(EmscriptenMixin, LinkerEnvVarsMixin, ClangCCompiler):
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', exe_wrapper=None, **kwargs):
         if not is_cross:

mesonbuild/compilers/cpp.py

@@ -36,7 +36,7 @@ from .mixins.intel import IntelGnuLikeCompiler, IntelVisualStudioLikeCompiler
 from .mixins.clang import ClangCompiler
 from .mixins.elbrus import ElbrusCompiler
 from .mixins.pgi import PGICompiler
-from .mixins.islinker import BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin
+from .mixins.islinker import LinkerEnvVarsMixin
 from .mixins.emscripten import EmscriptenMixin
 
 if T.TYPE_CHECKING:
@@ -201,7 +201,7 @@ class AppleClangCPPCompiler(ClangCPPCompiler):
     pass
 
 
-class EmscriptenCPPCompiler(EmscriptenMixin, BasicLinkerIsCompilerMixin, LinkerEnvVarsMixin, ClangCPPCompiler):
+class EmscriptenCPPCompiler(EmscriptenMixin, LinkerEnvVarsMixin, ClangCPPCompiler):
     def __init__(self, exelist, version, for_machine: MachineChoice,
                  is_cross: bool, info: 'MachineInfo', exe_wrapper=None, **kwargs):
         if not is_cross:

mesonbuild/compilers/mixins/emscripten.py

@@ -18,7 +18,6 @@ import os.path
 import typing as T
 
 from ... import coredata
-from ...mesonlib import MesonException
 
 if T.TYPE_CHECKING:
     from ..environment import Environment
@@ -26,18 +25,6 @@ if T.TYPE_CHECKING:
 
 class EmscriptenMixin:
 
-    def get_option_link_args(self, options):
-        return []
-
-    def get_soname_args(self, *args, **kwargs):
-        raise MesonException('Emscripten does not support shared libraries.')
-
-    def get_allow_undefined_link_args(self) -> T.List[str]:
-        return ['-s', 'ERROR_ON_UNDEFINED_SYMBOLS=0']
-
-    def get_linker_output_args(self, output: str) -> T.List[str]:
-        return ['-o', output]
-
     def _get_compile_output(self, dirname, mode):
         # In pre-processor mode, the output is sent to stdout and discarded
         if mode == 'preprocess':
@@ -54,13 +41,6 @@ class EmscriptenMixin:
     def thread_flags(self, env: 'Environment') -> T.List[str]:
         return ['-s', 'USE_PTHREADS=1']
 
-    def thread_link_flags(self, env: 'Environment') -> T.List[str]:
-        args = ['-s', 'USE_PTHREADS=1']
-        count = env.coredata.compiler_options[self.for_machine]['{}_thread_count'.format(self.language)].value  # type: int
-        if count:
-            args.extend(['-s', 'PTHREAD_POOL_SIZE={}'.format(count)])
-        return args
-
     def get_options(self):
         opts = super().get_options()
         opts.update({

mesonbuild/environment.py

@@ -58,6 +58,7 @@ from .linkers import (
     XilinkDynamicLinker,
     CudaLinker,
     VisualStudioLikeLinkerMixin,
+    WASMDynamicLinker,
 )
 from functools import lru_cache
 from .compilers import (
@@ -957,9 +958,18 @@ class Environment:
             if 'Emscripten' in out:
                 cls = EmscriptenCCompiler if lang == 'c' else EmscriptenCPPCompiler
                 self.coredata.add_lang_args(cls.language, cls, for_machine, self)
+                # emcc cannot be queried to get the version out of it (it
+                # ignores -Wl,--version and doesn't have an alternative).
+                # Further, wasm-id *is* lld and will return `LLD X.Y.Z` if you
+                # call `wasm-ld --version`, but a special version of lld that
+                # takes different options.
+                p, o, _ = Popen_safe(['wasm-ld', '--version'])
+                linker = WASMDynamicLinker(
+                    compiler, for_machine, cls.LINKER_PREFIX,
+                    [], version=search_version(o))
                 return cls(
                     ccache + compiler, version, for_machine, is_cross, info,
-                    exe_wrap, full_version=full_version)
+                    exe_wrap, linker=linker, full_version=full_version)
 
             if 'armclang' in out:
                 # The compiler version is not present in the first line of output,

mesonbuild/linkers.py

@@ -693,6 +693,35 @@ class LLVMDynamicLinker(GnuLikeDynamicLinkerMixin, PosixDynamicLinkerMixin, Dyna
         return []
 
 
+class WASMDynamicLinker(GnuLikeDynamicLinkerMixin, PosixDynamicLinkerMixin, DynamicLinker):
+
+    """Emscripten's wasm-ld."""
+
+    def __init__(self, *args, **kwargs):
+        super().__init__('ld.wasm', *args, **kwargs)
+
+    def thread_link_flags(self, env: 'Environment') -> T.List[str]:
+        args = ['-s', 'USE_PTHREADS=1']
+        count = env.coredata.compiler_options[self.for_machine]['{}_thread_count'.format(self.language)].value  # type: int
+        if count:
+            args.extend(['-s', 'PTHREAD_POOL_SIZE={}'.format(count)])
+        return args
+
+    def get_allow_undefined_args(self) -> T.List[str]:
+        return ['-s', 'ERROR_ON_UNDEFINED_SYMBOLS=0']
+
+    def no_undefined_args(self) -> T.List[str]:
+        return ['-s', 'ERROR_ON_UNDEFINED_SYMBOLS=1']
+
+    def get_soname_args(self, env: 'Environment', prefix: str, shlib_name: str,
+                        suffix: str, soversion: str, darwin_versions: T.Tuple[str, str],
+                        is_shared_module: bool) -> T.List[str]:
+        raise mesonlib.MesonException('{} does not support shared libraries.'.format(self.id))
+
+    def get_asneeded_args(self) -> T.List[str]:
+        return []
+
+
 class CcrxDynamicLinker(DynamicLinker):
 
     """Linker for Renesis CCrx compiler."""