daemon: Allow check builds of 'builtin:download' derivations.

Fixes <http://bugs.gnu.org/25089>.
Reported by Leo Famulari <leo@famulari.name>.

* nix/libstore/build.cc (DerivationGoal::runChild): In the 'isBuiltin'
case, check whether DRV's output is in 'redirectedOutputs', and pass an
'output' argument to the built-in builder.
(DerivationGoal::addHashRewrite): Add 'printMsg' call.
* nix/libstore/builtins.hh (derivationBuilder): Add 'output' parameter.
* nix/libstore/builtins.cc (builtinDownload): Likewise.
Add OUTPUT to ARGV.
* guix/scripts/perform-download.scm (perform-download): Add 'output'
parameter.
(guix-perform-download): Adjust 'match' clauses accordingly.
* tests/derivations.scm ("'download' built-in builder, check mode"): New
test.

1 files changed, 13 insertions, 2 deletions

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index 38048ceebc..cebc404d1c 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2271,8 +2271,17 @@ void DerivationGoal::runChild()
                 logType = ltFlat;
 
 		auto buildDrv = lookupBuiltinBuilder(drv.builder);
-                if (buildDrv != NULL)
-                    buildDrv(drv, drvPath);
+                if (buildDrv != NULL) {
+		    /* Check what the output file name is.  When doing a
+		       'bmCheck' build, the output file name is different from
+		       that specified in DRV due to hash rewriting.  */
+		    Path output = drv.outputs["out"].path;
+		    auto redirected = redirectedOutputs.find(output);
+		    if (redirected != redirectedOutputs.end())
+			output = redirected->second;
+
+                    buildDrv(drv, drvPath, output);
+		}
                 else
                     throw Error(format("unsupported builtin function '%1%'") % string(drv.builder, 8));
                 _exit(0);
@@ -2742,6 +2751,8 @@ Path DerivationGoal::addHashRewrite(const Path & path)
     rewritesToTmp[h1] = h2;
     rewritesFromTmp[h2] = h1;
     redirectedOutputs[path] = p;
+    printMsg(lvlChatty, format("output '%1%' redirected to '%2%'")
+	     % path % p);
     return p;
 }