Introduce circular-dependencies.py

This script can be used to find circular include dependencies in the
code base. These should eventually be weeded out.

contrib/devtools/circular-dependencies.py

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+
+import sys
+import re
+
+MAPPING = {
+    'core_read.cpp': 'core_io.cpp',
+    'core_write.cpp': 'core_io.cpp',
+}
+
+# Directories with header-based modules, where the assumption that .cpp files
+# define functions and variables declared in corresponding .h files is
+# incorrect.
+HEADER_MODULE_PATHS = [
+    'interfaces/'
+]
+
+def module_name(path):
+    if path in MAPPING:
+        path = MAPPING[path]
+    if any(path.startswith(dirpath) for dirpath in HEADER_MODULE_PATHS):
+        return path
+    if path.endswith(".h"):
+        return path[:-2]
+    if path.endswith(".c"):
+        return path[:-2]
+    if path.endswith(".cpp"):
+        return path[:-4]
+    return None
+
+files = dict()
+deps = dict()
+
+RE = re.compile("^#include \"(.*)\"")
+
+# Iterate over files, and create list of modules
+for arg in sys.argv[1:]:
+    module = module_name(arg)
+    if module is None:
+        print("Ignoring file %s (does not constitute module)\n" % arg)
+    else:
+        files[arg] = module
+        deps[module] = set()
+
+# Iterate again, and build list of direct dependencies for each module
+# TODO: implement support for multiple include directories
+for arg in sorted(files.keys()):
+    module = files[arg]
+    with open(arg, 'r', encoding="utf8") as f:
+        for line in f:
+            match = RE.match(line)
+            if match:
+                include = match.group(1)
+                included_module = module_name(include)
+                if included_module is not None and included_module in deps and included_module != module:
+                    deps[module].add(included_module)
+
+# Loop to find the shortest (remaining) circular dependency
+have_cycle = False
+while True:
+    shortest_cycle = None
+    for module in sorted(deps.keys()):
+        # Build the transitive closure of dependencies of module
+        closure = dict()
+        for dep in deps[module]:
+            closure[dep] = []
+        while True:
+            old_size = len(closure)
+            old_closure_keys = sorted(closure.keys())
+            for src in old_closure_keys:
+                for dep in deps[src]:
+                    if dep not in closure:
+                        closure[dep] = closure[src] + [src]
+            if len(closure) == old_size:
+                break
+        # If module is in its own transitive closure, it's a circular dependency; check if it is the shortest
+        if module in closure and (shortest_cycle is None or len(closure[module]) + 1 < len(shortest_cycle)):
+            shortest_cycle = [module] + closure[module]
+    if shortest_cycle is None:
+        break
+    # We have the shortest circular dependency; report it
+    module = shortest_cycle[0]
+    print("Circular dependency: %s" % (" -> ".join(shortest_cycle + [module])))
+    # And then break the dependency to avoid repeating in other cycles
+    deps[shortest_cycle[-1]] = deps[shortest_cycle[-1]] - set([module])
+    have_cycle = True
+
+sys.exit(1 if have_cycle else 0)