#810, don't hash files in &%> if you don't have to

ndmitchell · Sep 5, 2021 · 458ecd5 · 458ecd5
1 parent b2aad78
commit 458ecd5
Show file tree

Hide file tree

Showing 2 changed files with 4 additions and 1 deletion.
diff --git a/CHANGES.txt b/CHANGES.txt
@@ -1,5 +1,6 @@
 Changelog for Shake (* = breaking change)
 
+    #810, don't hash files in &%> if you don't have to
 0.19.5, released 2021-07-04
     #807, fix space leak in Database module
     #796, fix a bug with newCache dependencies

diff --git a/src/Development/Shake/Internal/Rules/Files.hs b/src/Development/Shake/Internal/Rules/Files.hs
@@ -119,7 +119,9 @@ ruleRun opts rebuildFlags k o@(fmap getEx -> old :: Maybe Result) mode = do
             case v of
                 Just v -> case filesEqualValue opts old v of
                     NotEqual -> rebuild
-                    EqualCheap -> pure $ RunResult ChangedNothing (fromJust o) v
+                    -- See #810, important we pass old (which can be cheaply evaluated)
+                    -- and not v, which might have some lazily-evaluated file hashes in
+                    EqualCheap -> pure $ RunResult ChangedNothing (fromJust o) old
                     EqualExpensive -> pure $ RunResult ChangedStore (runBuilder $ putEx $ Result ver v) v
                 Nothing -> rebuild
         _ -> rebuild