Enhance Rust support

- Adds a `crate_type` kwarg to library targets, allowing the different
  types of Rust [linkage][1].
- Shared libraries use the `dylib` crate type by default, but can also
  be `cdylib`
- Static libraries use the `rlib` crate type by default, but can also
  be `staticlib`
- If any Rust target has shared library dependencies, add the
  appropriate linker arguments, including rpath for the sysroot of the
  Rust compiler

[1]: https://doc.rust-lang.org/reference/linkage.html

3 files changed, 67 insertions, 9 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index 40a05bf..5764b54 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -1157,8 +1157,10 @@ int dummy;
         args = ['--crate-type']
         if isinstance(target, build.Executable):
             cratetype = 'bin'
+        elif hasattr(target, 'crate_type'):
+            cratetype = target.crate_type
         elif isinstance(target, build.SharedLibrary):
-            cratetype = 'rlib'
+            cratetype = 'dylib'
         elif isinstance(target, build.StaticLibrary):
             cratetype = 'rlib'
         else:
@@ -1177,6 +1179,23 @@ int dummy;
             if d == '':
                 d = '.'
             args += ['-L', d]
+        has_shared_deps = False
+        for dep in target.get_dependencies():
+            if isinstance(dep, build.SharedLibrary):
+                has_shared_deps = True
+        if isinstance(target, build.SharedLibrary) or has_shared_deps:
+            # add prefer-dynamic if any of the Rust libraries we link
+            # against are dynamic, otherwise we'll end up with
+            # multiple implementations of crates
+            args += ['-C', 'prefer-dynamic']
+            # build the usual rpath arguments as well...
+            rpath_args = rustc.build_rpath_args(self.environment.get_build_dir(),
+                                                self.determine_rpath_dirs(target),
+                                                target.install_rpath)
+            # ... but then add rustc's sysroot to account for rustup
+            # installations
+            for rpath_arg in rpath_args:
+                args += ['-C', 'link-arg=' + rpath_arg + ':' + os.path.join(rustc.get_sysroot(), 'lib')]
         element = NinjaBuildElement(self.all_outputs, target_name, 'rust_COMPILER', relsrc)
         if len(orderdeps) > 0:
             element.add_orderdep(orderdeps)
@@ -1184,6 +1203,8 @@ int dummy;
         element.add_item('targetdep', depfile)
         element.add_item('cratetype', cratetype)
         element.write(outfile)
+        if isinstance(target, build.SharedLibrary):
+            self.generate_shsym(outfile, target)
 
     def swift_module_file_name(self, target):
         return os.path.join(self.get_target_private_dir(target),
diff --git a/mesonbuild/build.py b/mesonbuild/build.py
index 2c55ed4..f4b3382 100644
--- a/mesonbuild/build.py
+++ b/mesonbuild/build.py
@@ -71,6 +71,7 @@ known_lib_kwargs.update({'version': True, # Only for shared libs
                          'vala_vapi': True,
                          'vala_gir': True,
                          'pic': True, # Only for static libs
+                         'crate_type': True, # Only for Rust libs
                          })
 
 
@@ -1123,6 +1124,14 @@ class StaticLibrary(BuildTarget):
         super().__init__(name, subdir, subproject, is_cross, sources, objects, environment, kwargs)
         if 'cs' in self.compilers:
             raise InvalidArguments('Static libraries not supported for C#.')
+        if 'rust' in self.compilers:
+            # If no crate type is specified, or it's the generic lib type, use rlib
+            if not hasattr(self, 'crate_type') or self.crate_type == 'lib':
+                mlog.debug('Defaulting Rust static library target crate type to rlib')
+                self.crate_type = 'rlib'
+            # Don't let configuration proceed with a non-static crate type
+            elif self.crate_type not in ['rlib', 'staticlib']:
+                raise InvalidArguments('Crate type "{0}" invalid for static libraries; must be "rlib" or "staticlib"'.format(self.crate_type))
         # By default a static library is named libfoo.a even on Windows because
         # MSVC does not have a consistent convention for what static libraries
         # are called. The MSVC CRT uses libfoo.lib syntax but nothing else uses
@@ -1133,9 +1142,12 @@ class StaticLibrary(BuildTarget):
         if not hasattr(self, 'prefix'):
             self.prefix = 'lib'
         if not hasattr(self, 'suffix'):
-            # Rust static library crates have .rlib suffix
             if 'rust' in self.compilers:
-                self.suffix = 'rlib'
+                if not hasattr(self, 'crate_type') or self.crate_type == 'rlib':
+                    # default Rust static library suffix
+                    self.suffix = 'rlib'
+                elif self.crate_type == 'staticlib':
+                    self.suffix = 'a'
             else:
                 self.suffix = 'a'
         self.filename = self.prefix + self.name + '.' + self.suffix
@@ -1147,6 +1159,15 @@ class StaticLibrary(BuildTarget):
     def check_unknown_kwargs(self, kwargs):
         self.check_unknown_kwargs_int(kwargs, known_lib_kwargs)
 
+    def process_kwargs(self, kwargs, environment):
+        super().process_kwargs(kwargs, environment)
+        if 'crate_type' in kwargs:
+            crate_type = kwargs['crate_type']
+            if isinstance(crate_type, str):
+                self.crate_type = crate_type
+            else:
+                raise InvalidArguments('Invalid crate_type "{0}": must be a string.'.format(crate_type))
+
 class SharedLibrary(BuildTarget):
     def __init__(self, name, subdir, subproject, is_cross, sources, objects, environment, kwargs):
         self.soversion = None
@@ -1159,6 +1180,14 @@ class SharedLibrary(BuildTarget):
         # The import library that GCC would generate (and prefer)
         self.gcc_import_filename = None
         super().__init__(name, subdir, subproject, is_cross, sources, objects, environment, kwargs)
+        if 'rust' in self.compilers:
+            # If no crate type is specified, or it's the generic lib type, use dylib
+            if not hasattr(self, 'crate_type') or self.crate_type == 'lib':
+                mlog.debug('Defaulting Rust dynamic library target crate type to "dylib"')
+                self.crate_type = 'dylib'
+            # Don't let configuration proceed with a non-dynamic crate type
+            elif self.crate_type not in ['dylib', 'cdylib']:
+                raise InvalidArguments('Crate type "{0}" invalid for dynamic libraries; must be "dylib" or "cdylib"'.format(self.crate_type))
         if not hasattr(self, 'prefix'):
             self.prefix = None
         if not hasattr(self, 'suffix'):
@@ -1200,12 +1229,6 @@ class SharedLibrary(BuildTarget):
             prefix = ''
             suffix = 'dll'
             self.filename_tpl = '{0.prefix}{0.name}.{0.suffix}'
-        # Rust
-        elif 'rust' in self.compilers:
-            # Currently, we always build --crate-type=rlib
-            prefix = 'lib'
-            suffix = 'rlib'
-            self.filename_tpl = '{0.prefix}{0.name}.{0.suffix}'
         # C, C++, Swift, Vala
         # Only Windows uses a separate import library for linking
         # For all other targets/platforms import_filename stays None
@@ -1315,6 +1338,12 @@ class SharedLibrary(BuildTarget):
                 raise InvalidArguments(
                     'Shared library vs_module_defs must be either a string, '
                     'a file object or a Custom Target')
+        if 'crate_type' in kwargs:
+            crate_type = kwargs['crate_type']
+            if isinstance(crate_type, str):
+                self.crate_type = crate_type
+            else:
+                raise InvalidArguments('Invalid crate_type "{0}": must be a string.'.format(crate_type))
 
     def check_unknown_kwargs(self, kwargs):
         self.check_unknown_kwargs_int(kwargs, known_lib_kwargs)
diff --git a/mesonbuild/compilers.py b/mesonbuild/compilers.py
index c9cfb46..6e7283c 100644
--- a/mesonbuild/compilers.py
+++ b/mesonbuild/compilers.py
@@ -1809,6 +1809,14 @@ class RustCompiler(Compiler):
     def get_buildtype_args(self, buildtype):
         return rust_buildtype_args[buildtype]
 
+    def build_rpath_args(self, build_dir, rpath_paths, install_rpath):
+        return build_unix_rpath_args(build_dir, rpath_paths, install_rpath)
+
+    def get_sysroot(self):
+        cmd = self.exelist + ['--print', 'sysroot']
+        p, stdo, stde = Popen_safe(cmd)
+        return stdo.split('\n')[0]
+
 class SwiftCompiler(Compiler):
     def __init__(self, exelist, version):
         self.language = 'swift'