Allow dynamic derivation deps in `inputDrvs`

We use the same nested map representation we used for goals, again in
order to save space. We might someday want to combine with `inputDrvs`,
by doing `V = bool` instead of `V = std::set<OutputName>`, but we are
not doing that yet for sake of a smaller diff.

The ATerm format for Derivations also needs to be extended, in addition
to the in-memory format. To accomodate this, we added a new basic
versioning scheme, so old versions of Nix will get nice errors. (And
going forward, if the ATerm format changes again the errors will be even
better.)

`parsedStrings`, an internal function used as part of parsing
derivations in A-Term format, used to consume the final `]` but expect
the initial `[` to already be consumed. This made for what looked like
unbalanced brackets at callsites, which was confusing. Now it consumes
both which is hopefully less confusing.

As part of testing, we also created a unit test for the A-Term format for
regular non-experimental derivations too.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>

Apply suggestions from code review

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/libstore/derived-path-map.hh b/src/libstore/derived-path-map.hh
index 9ce58206e..4a2c90733 100644
--- a/src/libstore/derived-path-map.hh
+++ b/src/libstore/derived-path-map.hh
@@ -48,6 +48,8 @@ struct DerivedPathMap {
          * The map of the root node.
          */
         Map childMap;
+
+        DECLARE_CMP(ChildNode);
     };
 
     /**
@@ -60,6 +62,8 @@ struct DerivedPathMap {
      */
     Map map;
 
+    DECLARE_CMP(DerivedPathMap);
+
     /**
      * Find the node for `k`, creating it if needed.
      *
@@ -68,6 +72,27 @@ struct DerivedPathMap {
      * by changing this node.
      */
     ChildNode & ensureSlot(const SingleDerivedPath & k);
+
+    /**
+     * Like `ensureSlot` but does not create the slot if it doesn't exist.
+     *
+     * Read the entire description of `ensureSlot` to understand an
+     * important caveat here that "have slot" does *not* imply "key is
+     * set in map". To ensure a key is set one would need to get the
+     * child node (with `findSlot` or `ensureSlot`) *and* check the
+     * `ChildNode::value`.
+     */
+    ChildNode * findSlot(const SingleDerivedPath & k);
 };
 
+
+DECLARE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>::,
+    DerivedPathMap<std::set<std::string>>);
+DECLARE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>::ChildNode::,
+    DerivedPathMap<std::set<std::string>>::ChildNode);
+
 }