Adjust style guide (loops) and add unreachable macro

docs/STYLE_GUIDE.md

@@ -120,13 +120,13 @@ duplicating documentation.
 
 - Exceed 70 lines of code per function only in exceptional circumstances. Aim
   for less.
-- No `while` in production. All `for` loops must have a maximum number of
-  passes.
+- Prefer `for` loops over `while` loops. All loops (of any kind) must have a
+  maximum number of passes.
 - Use depth checks when using recursion in production. Use recursion only if the
   algorithm is defined using recursion.
 - Avoid `mut` in production code if possible without much pain.
-- Mark all extrinsics `transactional`, even if they satisfy
-  the verify-first/write-later principle.
+- Mark all extrinsics `transactional`, even if they satisfy the
+  verify-first/write-later principle.
 - Avoid indentation over five levels; never go over seven levels.
 - All public functions must be documented. Documentation of `pub(crate)` and
   private functions is optional but encouraged.
@@ -156,3 +156,17 @@ duplicating documentation.
 - For larger modules, use one test file per extrinsic for unit tests. Make unit
   tests as decoupled as possible from other modules. Place end-to-end and
   integration tests in extra files.
+- If possible, test unreachable code and states thought to be impossible using
+  the following schema:
+
+```rust
+// In code logic
+zeitgeist_primitives::unreachable_non_terminating!(condition, log_target, message)
+```
+
+```rust
+// In test
+#[test]
+#[should_panic(expected = message)]
+// Cause assertion
+```

primitives/src/macros.rs

@@ -0,0 +1,66 @@
+// Copyright 2024 Forecasting Technologies LTD.
+//
+// This file is part of Zeitgeist.
+//
+// Zeitgeist is free software: you can redistribute it and/or modify it
+// under the terms of the GNU General Public License as published by the
+// Free Software Foundation, either version 3 of the License, or (at
+// your option) any later version.
+//
+// Zeitgeist is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Zeitgeist. If not, see <https://www.gnu.org/licenses/>.
+
+/// This macro does ensure that a condition `$condition` is met, and if it is not met
+/// it will log a message `$message` with optional message arguments `message_args` to
+/// an optional log target `$log_target`, cause an assertion in a test environment
+/// and execute some optional extra code.
+#[macro_export]
+macro_rules! unreachable_non_terminating {
+    ($condition: expr, $message: literal, $($message_args: tt)*) => {
+        let message = format!($message, $($message_args)*);
+
+        #[cfg(test)]
+        assert!($condition, "{}", message);
+
+        if !$condition {
+            log::warn!("{}", message);
+        }
+    };
+    ($condition: expr, $log_target: ident, $message: literal, $($message_args: tt)*) => {
+        let message = format!($message, $($message_args)*);
+
+        #[cfg(test)]
+        assert!($condition, "{}", message);
+
+        if !$condition {
+            log::warn!(target: $log_target, "{}", message);
+        }
+    };
+    ($condition: expr, $extra_code: expr, $message: literal, $($message_args: tt)*) => {
+        let message = format!($message, $($message_args)*);
+
+        #[cfg(test)]
+        assert!($condition, "{}", message);
+
+        if !$condition {
+            log::warn!("{}", message);
+            $extra_code;
+        }
+    };
+    ($condition: expr, $log_target: ident, $extra_code: expr, $message: literal, $($message_args: tt)*) => {
+        let message = format!($message, $($message_args)*);
+
+        #[cfg(test)]
+        assert!($condition, "{}", message);
+
+        if !$condition {
+            log::warn!(target: $log_target, "{}", message);
+            $extra_code;
+        }
+    };
+}