BuildResult: Add a "Cancelled" status

This denotes the result of a build that didn't succeed or fail, but
was cancelled because some other goal failed and --keep-going was not
enabled.

src/libstore/build-result.cc

@@ -40,7 +40,7 @@ static BuildResult::Success::Status successStatusFromString(std::string_view str
     throw Error("unknown built result success status '%s'", str);
 }
 
-static constexpr std::array<std::pair<BuildResult::Failure::Status, std::string_view>, 12> failureStatusStrings{{
+static constexpr std::array<std::pair<BuildResult::Failure::Status, std::string_view>, 13> failureStatusStrings{{
 #define ENUM_ENTRY(e) {BuildResult::Failure::e, #e}
     ENUM_ENTRY(PermanentFailure),
     ENUM_ENTRY(InputRejected),
@@ -54,6 +54,7 @@ static constexpr std::array<std::pair<BuildResult::Failure::Status, std::string_
     ENUM_ENTRY(NotDeterministic),
     ENUM_ENTRY(NoSubstituters),
     ENUM_ENTRY(HashMismatch),
+    ENUM_ENTRY(Cancelled),
 #undef ENUM_ENTRY
 }};
 

src/libstore/include/nix/store/build-result.hh

@@ -74,6 +74,7 @@ struct BuildResult
             /// know about this one, so change it back to `OutputRejected`
             /// before serialization.
             HashMismatch = 15,
+            Cancelled = 16,
         } status = MiscFailure;
 
         /**

src/libstore/include/nix/store/build/goal.hh

@@ -109,7 +109,7 @@ public:
     /**
      * Build result.
      */
-    BuildResult buildResult;
+    BuildResult buildResult = {.inner = BuildResult::Failure{.status = BuildResult::Failure::Cancelled}};
 
     /**
      * Suspend our goal and wait until we get `work`-ed again.