Restore the hash mismatch activity

src/libstore/build/derivation-goal.cc

@@ -872,6 +872,7 @@ Goal::Co DerivationGoal::tryToBuild()
                     *drvOptions,
                     inputPaths,
                     initialOutputs,
+                    act
                 });
         }
 

src/libstore/unix/build/derivation-builder.cc

@@ -2709,14 +2709,12 @@ SingleDrvOutputs DerivationBuilderImpl::registerOutputs()
                             store.printStorePath(drvPath),
                             wanted.to_string(HashFormat::SRI, true),
                             got.to_string(HashFormat::SRI, true)));
-#if 0 // FIXME
                     act->result(resHashMismatch,
                         {
                             {"storePath", store.printStorePath(drvPath)},
                             {"wanted", wanted},
                             {"got", got},
                         });
-#endif
                 }
                 if (!newInfo0.references.empty()) {
                     auto numViolations = newInfo.references.size();

src/libstore/unix/include/nix/store/build/derivation-builder.hh

@@ -58,6 +58,11 @@ struct DerivationBuilderParams
 
     const BuildMode & buildMode;
 
+    /**
+     * The activity corresponding to the build.
+     */
+    std::unique_ptr<Activity> & act;
+
     DerivationBuilderParams(
         const StorePath & drvPath,
         const BuildMode & buildMode,
@@ -66,7 +71,8 @@ struct DerivationBuilderParams
         const StructuredAttrs * parsedDrv,
         const DerivationOptions & drvOptions,
         const StorePathSet & inputPaths,
-        std::map<std::string, InitialOutput> & initialOutputs)
+        std::map<std::string, InitialOutput> & initialOutputs,
+        std::unique_ptr<Activity> & act)
         : drvPath{drvPath}
         , buildResult{buildResult}
         , drv{drv}
@@ -75,6 +81,7 @@ struct DerivationBuilderParams
         , inputPaths{inputPaths}
         , initialOutputs{initialOutputs}
         , buildMode{buildMode}
+        , act{act}
     { }
 
     DerivationBuilderParams(DerivationBuilderParams &&) = default;