Simplify hook tool implementation

The "hook tools" were capable of hooking into many commands run by the build system.
To my knowlage, the only hook is the "post-build-hook". The post build hook could be
easier to reason about if the implementation is specialized for just post-build
hooking.

This commit make it much easier to point out where post build hooks are called by
making the call explicit.

Author: theotherjimmy

tools/hooks.py

@@ -355,7 +355,7 @@ def is_PSA_secure_target(self):
     def is_PSA_non_secure_target(self):
         return 'NSPE_Target' in self.labels
 
-    def init_hooks(self, hook, toolchain):
+    def get_post_build_hook(self, toolchain):
         """Initialize the post-build hooks for a toolchain. For now, this
         function only allows "post binary" hooks (hooks that are executed
         after the binary image is extracted from the executable file)
@@ -404,8 +404,7 @@ def init_hooks(self, hook, toolchain):
         if toolchain_restrictions and \
            not toolchain_labels.intersection(toolchain_restrictions):
             return
-        # Finally, hook the requested function
-        hook.hook_add_binary("post", getattr(cls, function_name))
+        return getattr(cls, function_name)
 
 ################################################################################
 # Target specific code goes in this section

tools/targets/__init__.py

@@ -36,7 +36,6 @@
 from ..utils import (run_cmd, mkdir, rel_path, ToolException,
                     NotSupportedException, split_path, compile_worker)
 from ..settings import MBED_ORG_USER, PRINT_COMPILER_OUTPUT_AS_LINK
-from .. import hooks
 from ..notifier.term import TerminalNotifier
 from ..resources import FileType
 from ..memap import MemapParser
@@ -96,7 +95,7 @@ def __init__(self, target, notify=None, macros=None, build_profile=None,
         self.name = self.__class__.__name__
 
         # compile/assemble/link/binary hooks
-        self.hook = hooks.Hook(target, self)
+        self._post_build_hook = target.get_post_build_hook(self.name)
 
         # Toolchain flags
         self.flags = deepcopy(build_profile or self.profile_template)
@@ -653,6 +652,9 @@ def link_program(self, r, tmp_path, name):
             self.progress("elf2bin", name)
             self.binary(r, elf, bin)
 
+        if self._post_build_hook:
+            self.progress("post-build", name)
+            self._post_build_hook(self, r, elf, bin)
         # Initialize memap and process map file. This doesn't generate output.
         self.mem_stats(mapfile)
 
@@ -1002,9 +1004,6 @@ def assemble(self, source, object, includes):
 
         Side effects:
         None
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented
 
@@ -1024,9 +1023,6 @@ def compile_c(self, source, object, includes):
 
         Side effects:
         None
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented
 
@@ -1046,9 +1042,6 @@ def compile_cpp(self, source, object, includes):
 
         Side effects:
         None
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented
 
@@ -1068,9 +1061,6 @@ def link(self, output, objects, libraries, lib_dirs, mem_map):
 
         Side effect:
         Runs the linker to produce the executable.
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented
 
@@ -1087,9 +1077,6 @@ def archive(self, objects, lib_path):
 
         Side effect:
         Runs the archiving tool to produce the library file.
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented
 
@@ -1107,9 +1094,6 @@ def binary(self, resources, elf, bin):
 
         Side effect:
         Runs the elf2bin tool to produce the simplified binary file.
-
-        Note:
-        This method should be decorated with @hook_tool.
         """
         raise NotImplemented