Introduce `SingleDrvOutputs`

In many cases we are dealing with a collection of realisations, they are
all outputs of the same derivation. In that case, we don't need
"derivation hashes modulos" to be part of our map key, because the
output names alone will be unique. Those hashes are still part of the
realisation proper, so we aren't loosing any information, we're just
"normalizing our schema" by narrowing the "primary key".

Besides making our data model a bit "tighter" this allows us to avoid a
double `for` loop in `DerivationGoal::waiteeDone`. The inner `for` loop
was previously just to select the output we cared about without knowing
its hash. Now we can just select the output by name directly.

Note that neither protocol is changed as part of this: we are still
transferring `DrvOutputs` over the wire for `BuildResult`s. I would only
consider revising this once #6223 is merged, and we can mention protocol
versions inside factored-out serialization logic. Until then it is
better not change anything because it would come a the cost of code
reuse.

1 files changed, 6 insertions, 6 deletions

diff --git a/src/libstore/build/derivation-goal.hh b/src/libstore/build/derivation-goal.hh
index 9b5bd1805..7033b7a58 100644
--- a/src/libstore/build/derivation-goal.hh
+++ b/src/libstore/build/derivation-goal.hh
@@ -253,7 +253,7 @@ struct DerivationGoal : public Goal
      * Check that the derivation outputs all exist and register them
      * as valid.
      */
-    virtual DrvOutputs registerOutputs();
+    virtual SingleDrvOutputs registerOutputs();
 
     /**
      * Open a log file and a pipe to it.
@@ -306,17 +306,17 @@ struct DerivationGoal : public Goal
      * Update 'initialOutputs' to determine the current status of the
      * outputs of the derivation. Also returns a Boolean denoting
      * whether all outputs are valid and non-corrupt, and a
-     * 'DrvOutputs' structure containing the valid and wanted
+     * 'SingleDrvOutputs' structure containing the valid and wanted
      * outputs.
      */
-    std::pair<bool, DrvOutputs> checkPathValidity();
+    std::pair<bool, SingleDrvOutputs> checkPathValidity();
 
     /**
      * Aborts if any output is not valid or corrupt, and otherwise
-     * returns a 'DrvOutputs' structure containing the wanted
+     * returns a 'SingleDrvOutputs' structure containing the wanted
      * outputs.
      */
-    DrvOutputs assertPathValidity();
+    SingleDrvOutputs assertPathValidity();
 
     /**
      * Forcibly kill the child process, if any.
@@ -329,7 +329,7 @@ struct DerivationGoal : public Goal
 
     void done(
         BuildResult::Status status,
-        DrvOutputs builtOutputs = {},
+        SingleDrvOutputs builtOutputs = {},
         std::optional<Error> ex = {});
 
     void waiteeDone(GoalPtr waitee, ExitCode result) override;