measurestack: Fix+test skipmodel chain collections

1 files changed, 6 insertions, 6 deletions

diff --git a/build-aux/measurestack/analyze.py b/build-aux/measurestack/analyze.py
index 93bf885..f454b7e 100644
--- a/build-aux/measurestack/analyze.py
+++ b/build-aux/measurestack/analyze.py
@@ -232,10 +232,10 @@ class AnalyzeResult(typing.NamedTuple):
 class SkipModel(typing.NamedTuple):
     """Running the skipmodel calls `.fn(chain, ...)` with the chain
     consisting of the last `.nchain` items (if .nchain is an int), or
-    the chain starting with the *last* occurance of `.nchain` (if
-    .nchain is a collection).  If the chain is not that long or does
-    not contain a member of the collection, then .fn is not called and
-    the call is *not* skipped.
+    the chain starting with the *last* occurance of `.nchain` in
+    chain[:-1] (if .nchain is a collection).  If the chain is not that
+    long or does not contain a member of the collection, then .fn is
+    not called and the call is *not* skipped.
 
     """
 
@@ -248,9 +248,9 @@ class SkipModel(typing.NamedTuple):
                 _chain = chain[-self.nchain :]
                 return self.fn(_chain, call), len(_chain)
         else:
-            for i in reversed(range(len(chain))):
+            for i in reversed(range(len(chain) - 1)):
                 if chain[i].base() in self.nchain:
-                    _chain = chain[i - 1 :]
+                    _chain = chain[i:]
                     return self.fn(_chain, call), len(_chain)
         return False, 0