From 34752db1975bf1b2fcaaab5576b5ebc481c67e2b Mon Sep 17 00:00:00 2001
From: Max Ulidtko <ulidtko@gmail.com>
Date: Fri, 10 Jul 2026 18:25:37 +0200
Subject: [PATCH] Re #1476 Emit a Note-level hint when caching with
 --force-dirty

---
 src/Stack/Build/ExecutePackage.hs | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/Stack/Build/ExecutePackage.hs b/src/Stack/Build/ExecutePackage.hs
index 36f3207c89..717aa91388 100644
--- a/src/Stack/Build/ExecutePackage.hs
+++ b/src/Stack/Build/ExecutePackage.hs
@@ -128,7 +128,7 @@ import           Stack.Types.ComponentUtils
                    ( StackUnqualCompName, toCabalName, unqualCompToString
                    , unqualCompToText
                    )
-import           Stack.Types.Config ( Config (..), HasConfig (..) )
+import           Stack.Types.Config ( Config (..), HasConfig (..), buildOptsL )
 import           Stack.Types.ConfigureOpts
                    ( BaseConfigOpts (..), ConfigureOpts (..) )
 import           Stack.Types.Curator ( Curator (..) )
@@ -481,6 +481,7 @@ singleBuild
       case mprecompiled of
         Just precompiled ->
           copyPreCompiled isCInstTask ee task pkgId precompiled
+            <* warnImmutableCacheWithForceDirty
         Nothing -> do
           curator <- view $ buildConfigL . to (.curator)
           realConfigAndBuild
@@ -512,6 +513,19 @@ singleBuild
   enableBenchmarks = buildingFinals
     && componentEnableBenchmarks ck (taskComponents task)
 
+  -- Give a hint for surprisingly cached builds, https://github.com/commercialhaskell/stack/issues/1476
+  warnImmutableCacheWithForceDirty = do
+    forceDirtyFlagGiven <- view $ buildOptsL . to (.forceDirty)
+    targetsCLI <- view $ envConfigL . to (.buildOptsCLI.targetsCLI)
+    when (forceDirtyFlagGiven && fromPackageName (pkgName pkgId) `elem` targetsCLI) $ do
+      let pkg = fromPackageName (pkgName pkgId)
+      prettyNote $
+        fillSep [flow "Immutable snapshot package", style Current pkg, flow "picked from cached build despite --force-dirty."]
+        <> blankLine
+        <> flow "To force removal of cached build, try `stack exec -- ghc-pkg unregister --force " <+> pkg <> "`."
+        <> blankLine
+        <> flow "See Stack issue #1476 for more details."
+
 realConfigAndBuild ::
      forall env a. HasEnvConfig env
   => ActionContext