Improved profiling modes

[Joerg Henrichs (hiker)]

Closes #599.
It simplifies the definition of compilation profiles.

I added two commits for very minor cleanup of some tests (improved an error message, removed left-over debug print, and handled a warning, so pytest now reports all tests as green).

I have tested this with skeleton, lfric_atm, jules, um so far, and will verify that everything else is updated to use this new feature as well.

[Matthew Hambley (MatthewHambley)]

A few small things.

[Joerg Henrichs (hiker)]

Ready for next review.

[Joerg Henrichs (hiker)]

Looks like I forgot to re-request the review, sorry.

Note that there is a certain interaction with #603/#604 (python 3.14). Using class variables as done in this PR will not work with python 3.14 (unless it is switched to using fork, which is what #604 does). I.e. if in the future you want to switch back to the default fork behaviour, this code will actually fail. Possible solutions:

1. when implementing the new subprocess handling, we explicitly distribute ProfileFlags._inherit_from to the subprocesses, or:
2. We change the implementation to use instance attributes. This then needs to make sure that if profiling modes are added, all already existing instances are updated. To do this, the following patch keeps track of all instances, and will update all of them if a profile_mode is added. Admittedly quite hacky, but it can be portably implemented now, and won't break if python 3.14 subprocess handling is switched back in the future:

diff --git a/source/fab/tools/profile_flags.py b/source/fab/tools/profile_flags.py
index 07c3a2f..d8eb307 100644
--- a/source/fab/tools/profile_flags.py
+++ b/source/fab/tools/profile_flags.py
@@ -53,10 +53,13 @@ class ProfileFlags:
     # avoid having to handle "" as special case, it is added here
     # as an always available dummy profile.
     _inherit_from: dict[str, str] = {"": ""}
+    all_instances = []
 
     def __init__(self,
                  flags: Optional[Union[AbstractFlags, str, list[str]]] = None,
                  profile: str = "") -> None:
+        self._inherit_from = ProfileFlags._inherit_from.copy()
+        ProfileFlags.all_instances.append(self)
         # Stores the flags for each profile mode. The key is the (lower case)
         # name of the profile mode, and it contains a list of flags.
         # Initialise the dict with the default (empty) profile
@@ -93,6 +96,9 @@ class ProfileFlags:
         else:
             cls._inherit_from[name] = ""
 
+        for instance in ProfileFlags.all_instances:
+            instance._inherit_from = ProfileFlags._inherit_from.copy()
+
     def get_flags(self,
                   config: Optional["BuildConfig"] = None,
                   file_path: Optional[Path] = None) -> list[str]:
@@ -139,7 +145,7 @@ class ProfileFlags:
         else:
             profile = profile.lower()
 
-        if profile and profile not in ProfileFlags._inherit_from:
+        if profile and profile not in self._inherit_from:
             raise KeyError(f"Profile '{profile}' is not defined")
 
         # First add any flags that we inherit. This will recursively call

I am happy to add this patch here (or add anything better, it is quite hacky)

[Matthew Hambley (MatthewHambley)]

This change looks ready for trunk, pending the arrival of #604