Talk about assertions in CodingStandards.md

diff --git a/doc/HACKING/CodingStandards.md b/doc/HACKING/CodingStandards.md
index 55c23a7df528e3c49788dc5e478a519c5e61d030..a8fca4a77034a408370fc44a82d80e22c6a1d34d 100644 (file)
--- a/doc/HACKING/CodingStandards.md
+++ b/doc/HACKING/CodingStandards.md
@@ -249,7 +249,25 @@ end-users that they aren't expected to understand the message (perhaps
 with a string like "internal error"). Option (A) is to be preferred to
 option (B).
 
+Assertions In Tor
+-----------------
 
+Assertions should be used for bug-detection only.  Don't use assertions to
+detect bad user inputs, network errors, resource exhaustion, or similar
+issues.
+
+Tor is always built with assertions enabled, so try to only use
+`tor_assert()` for cases where you are absolutely sure that crashing is the
+least bad option.  Many bugs have been caused by use of `tor_assert()` when
+another kind of check would have been safer.
+
+If you're writing an assertion to test for a bug that you _can_ recover from,
+use `tor_assert_nonfatal()` in place of `tor_assert()`.  If you'd like to
+write a conditional that incorporates a nonfatal assertion, use the `BUG()`
+macro, as in:
+
+       if (BUG(ptr == NULL))
+               return -1;
 
 Doxygen comment conventions
 ---------------------------