Fix commercialhaskell#6565 Include Cabal flags set manually in the source map hash

Author: mpilgrem

ChangeLog.md

@@ -4,6 +4,11 @@
 
 Release notes:
 
+* The hash that Stack uses to distinguish one build plan from another has
+  changed for plans that set (as opposed to unset) manually Cabal flags for
+  immutable dependencies. This will cause Stack to rebuild dependencies for such
+  plans.
+
 **Changes since v2.15.6.1:**
 
 Major changes:
@@ -14,6 +19,10 @@ Other enhancements:
 
 Bug fixes:
 
+* The hashes that Stack uses to distinguish one build plan from another now
+  include the Cabal flags for immutable dependencies set manually. Previously,
+  in error, only such flags that were unset manually were included.
+
 ## v2.15.6.1 (release candidate)
 
 Release notes:

doc/build_command.md

@@ -281,13 +281,6 @@ This overrides:
     In order to set a Cabal flag for a GHC boot package, the package must be
     specified as an [extra-dep](yaml_configuration.md#extra-deps).
 
-!!! warning
-
-    Stack creates snapshots when building immutable dependencies of projects.
-    The names of Cabal flags that have been unset manually distinguish one such
-    snapshot from another. However, the names of Cabal flags that have been set
-    manually do not do so.
-
 ### `--[no-]force-dirty` flag
 
 Default: Disabled

doc/yaml_configuration.md

@@ -322,13 +322,6 @@ in the snapshot.
     In order to set a Cabal flag for a GHC boot package, the package must be
     specified as an [extra-dep](#extra-deps).
 
-!!! warning
-
-    Stack creates snapshots when building immutable dependencies of projects.
-    The names of Cabal flags that have been unset manually distinguish one such
-    snapshot from another. However, the names of Cabal flags that have been set
-    manually do not do so.
-
 ### drop-packages
 
 [:octicons-tag-24: 2.1.1](https://github.com/commercialhaskell/stack/releases/tag/v2.1.1)

src/Stack/Build/Source.hs

@@ -194,9 +194,7 @@ depPackageHashableContent dp =
     PLMutable _ -> pure ""
     PLImmutable pli -> do
       let flagToBs (f, enabled) =
-            if enabled
-              then ""
-              else "-" <> fromString (C.unFlagName f)
+            (if enabled then "" else "-") <> fromString (C.unFlagName f)
           flags = map flagToBs $ Map.toList dp.depCommon.flags
           ghcOptions = map display dp.depCommon.ghcOptions
           cabalConfigOpts = map display dp.depCommon.cabalConfigOpts