build: move default_install_dir to the Target classes

there is a huge amount of isinstance calls, this reduces the amount of
these calls while splitting up a rather big function. It also assosiates
every target type with theire default install directory.

mesonbuild/backend/backends.py

@@ -970,33 +970,6 @@ class Backend:
         with open(install_data_file, 'wb') as ofile:
             pickle.dump(d, ofile)
 
-    def get_target_install_dirs(self, t):
-        # Find the installation directory.
-        if isinstance(t, build.SharedModule):
-            default_install_dir = self.environment.get_shared_module_dir()
-        elif isinstance(t, build.SharedLibrary):
-            default_install_dir = self.environment.get_shared_lib_dir()
-        elif isinstance(t, build.StaticLibrary):
-            default_install_dir = self.environment.get_static_lib_dir()
-        elif isinstance(t, build.Executable):
-            default_install_dir = self.environment.get_bindir()
-        elif isinstance(t, build.CustomTarget):
-            default_install_dir = None
-        else:
-            assert(isinstance(t, build.BuildTarget))
-            # XXX: Add BuildTarget-specific install dir cases here
-            default_install_dir = self.environment.get_libdir()
-        outdirs = t.get_custom_install_dir()
-        if outdirs[0] is not None and outdirs[0] != default_install_dir and outdirs[0] is not True:
-            # Either the value is set to a non-default value, or is set to
-            # False (which means we want this specific output out of many
-            # outputs to not be installed).
-            custom_install_dir = True
-        else:
-            custom_install_dir = False
-            outdirs[0] = default_install_dir
-        return outdirs, custom_install_dir
-
     def get_target_link_deps_mappings(self, t, prefix):
         '''
         On macOS, we need to change the install names of all built libraries
@@ -1015,7 +988,7 @@ class Backend:
             if old in result:
                 continue
             fname = ld.get_filename()
-            outdirs, _ = self.get_target_install_dirs(ld)
+            outdirs, _ = ld.get_install_dir(self.environment)
             new = os.path.join(prefix, outdirs[0], fname)
             result.update({old: new})
         return result
@@ -1024,7 +997,7 @@ class Backend:
         for t in self.build.get_targets().values():
             if not t.should_install():
                 continue
-            outdirs, custom_install_dir = self.get_target_install_dirs(t)
+            outdirs, custom_install_dir = t.get_install_dir(self.environment)
             # Sanity-check the outputs and install_dirs
             num_outdirs, num_out = len(outdirs), len(t.get_outputs())
             if num_outdirs != 1 and num_outdirs != num_out:

mesonbuild/build.py

@@ -324,6 +324,20 @@ a hard error in the future.''' % name)
         self.build_always_stale = False
         self.option_overrides = {}
 
+    def get_install_dir(self, environment):
+        # Find the installation directory.
+        default_install_dir = self.get_default_install_dir(environment)
+        outdirs = self.get_custom_install_dir()
+        if outdirs[0] is not None and outdirs[0] != default_install_dir and outdirs[0] is not True:
+            # Either the value is set to a non-default value, or is set to
+            # False (which means we want this specific output out of many
+            # outputs to not be installed).
+            custom_install_dir = True
+        else:
+            custom_install_dir = False
+            outdirs[0] = default_install_dir
+        return outdirs, custom_install_dir
+
     def get_basename(self):
         return self.name
 
@@ -686,6 +700,9 @@ class BuildTarget(Target):
             result.update(i.get_link_dep_subdirs())
         return result
 
+    def get_default_install_dir(self, environment):
+        return environment.get_libdir()
+
     def get_custom_install_dir(self):
         return self.install_dir
 
@@ -1323,6 +1340,9 @@ class Executable(BuildTarget):
         # Only linkwithable if using export_dynamic
         self.is_linkwithable = self.export_dynamic
 
+    def get_default_install_dir(self, environment):
+        return environment.get_bindir()
+
     def description(self):
         '''Human friendly description of the executable'''
         return self.name
@@ -1384,6 +1404,9 @@ class StaticLibrary(BuildTarget):
         self.filename = self.prefix + self.name + '.' + self.suffix
         self.outputs = [self.filename]
 
+    def get_default_install_dir(self, environment):
+        return environment.get_static_lib_dir()
+
     def type_suffix(self):
         return "@sta"
 
@@ -1430,6 +1453,9 @@ class SharedLibrary(BuildTarget):
         self.basic_filename_tpl = '{0.prefix}{0.name}.{0.suffix}'
         self.determine_filenames(is_cross, environment)
 
+    def get_default_install_dir(self, environment):
+        return environment.get_shared_lib_dir()
+
     def determine_filenames(self, is_cross, env):
         """
         See https://github.com/mesonbuild/meson/pull/417 for details.
@@ -1701,6 +1727,10 @@ class SharedModule(SharedLibrary):
             raise MesonException('Shared modules must not specify the soversion kwarg.')
         super().__init__(name, subdir, subproject, is_cross, sources, objects, environment, kwargs)
 
+    def get_default_install_dir(self, environment):
+        return environment.get_shared_module_dir()
+
+
 class CustomTarget(Target):
     known_kwargs = set([
         'input',
@@ -1738,6 +1768,9 @@ class CustomTarget(Target):
             mlog.warning('Unknown keyword arguments in target %s: %s' %
                          (self.name, ', '.join(unknowns)))
 
+    def get_default_install_dir(self, environment):
+        return None
+
     def __lt__(self, other):
         return self.get_id() < other.get_id()