SCons: Validate dependencies for linked multimedia modules

This is still a bit hacky and eventually we should rework the way we handle
optional dependencies (especially with regard to builtin/system libs), but
it's a simple first step.

Fixes #39219.

SConstruct

@@ -86,6 +86,7 @@ env_base.__class__.add_library = methods.add_library
 env_base.__class__.add_program = methods.add_program
 env_base.__class__.CommandNoCache = methods.CommandNoCache
 env_base.__class__.disable_warnings = methods.disable_warnings
+env_base.__class__.module_check_dependencies = methods.module_check_dependencies
 
 env_base["x86_libtheora_opt_gcc"] = False
 env_base["x86_libtheora_opt_vc"] = False
@@ -607,9 +608,7 @@ if selected_platform in platform_list:
         env.Append(CPPDEFINES=["MINIZIP_ENABLED"])
 
     editor_module_list = ["regex"]
-    for x in editor_module_list:
+    if env["tools"] and not env.module_check_dependencies("tools", editor_module_list):
-        if not env["module_" + x + "_enabled"]:
-            if env["tools"]:
         print(
             "Build option 'module_" + x + "_enabled=no' cannot be used with 'tools=yes' (editor), "
             "only with 'tools=no' (export template)."

methods.py

@@ -231,6 +231,30 @@ def disable_module(self):
     self.disabled_modules.append(self.current_module)
 
 
+def module_check_dependencies(self, module, dependencies):
+    """
+    Checks if module dependencies are enabled for a given module,
+    and prints a warning if they aren't.
+    Meant to be used in module `can_build` methods.
+    Returns a boolean (True if dependencies are satisfied).
+    """
+    missing_deps = []
+    for dep in dependencies:
+        opt = "module_{}_enabled".format(dep)
+        if not opt in self or not self[opt]:
+            missing_deps.append(dep)
+
+    if missing_deps != []:
+        print(
+            "Disabling '{}' module as the following dependencies are not satisfied: {}".format(
+                module, ", ".join(missing_deps)
+            )
+        )
+        return False
+    else:
+        return True
+
+
 def use_windows_spawn_fix(self, platform=None):
 
     if os.name != "nt":

modules/opus/config.py

@@ -1,5 +1,5 @@
 def can_build(env, platform):
-    return True
+    return env.module_check_dependencies("opus", ["ogg"])
 
 
 def configure(env):

modules/theora/config.py

@@ -1,5 +1,5 @@
 def can_build(env, platform):
-    return True
+    return env.module_check_dependencies("theora", ["ogg", "vorbis"])
 
 
 def configure(env):

modules/vorbis/config.py

@@ -1,5 +1,5 @@
 def can_build(env, platform):
-    return True
+    return env.module_check_dependencies("vorbis", ["ogg"])
 
 
 def configure(env):

modules/webm/config.py

@@ -1,5 +1,8 @@
 def can_build(env, platform):
-    return platform not in ["iphone"]
+    if platform in ["iphone"]:
+        return False
+
+    return env.module_check_dependencies("webm", ["ogg", "opus", "vorbis"])
 
 
 def configure(env):