nix-shell: Use bashInteractive from <nixpkgs>

This adds about 0.1s to nix-shell runtime in the case where
bashInteractive already exists.

See discussion at https://github.com/NixOS/nixpkgs/issues/27493.

2 files changed, 7 insertions, 8 deletions

diff --git a/src/libexpr/get-drvs.cc b/src/libexpr/get-drvs.cc
index b7e16de7f..66689e3e8 100644
--- a/src/libexpr/get-drvs.cc
+++ b/src/libexpr/get-drvs.cc
@@ -267,15 +267,14 @@ static bool getDerivation(EvalState & state, Value & v,
 }
 
 
-bool getDerivation(EvalState & state, Value & v, DrvInfo & drv,
+std::experimental::optional<DrvInfo> getDerivation(EvalState & state, Value & v,
     bool ignoreAssertionFailures)
 {
     Done done;
     DrvInfos drvs;
     getDerivation(state, v, "", drvs, done, ignoreAssertionFailures);
-    if (drvs.size() != 1) return false;
-    drv = drvs.front();
-    return true;
+    if (drvs.size() != 1) return {};
+    return std::move(drvs.front());
 }
 
 
diff --git a/src/libexpr/get-drvs.hh b/src/libexpr/get-drvs.hh
index 82fb8a3ac..32294e458 100644
--- a/src/libexpr/get-drvs.hh
+++ b/src/libexpr/get-drvs.hh
@@ -75,10 +75,10 @@ typedef list<DrvInfo> DrvInfos;
 #endif
 
 
-/* If value `v' denotes a derivation, store information about the
-   derivation in `drv' and return true.  Otherwise, return false. */
-bool getDerivation(EvalState & state, Value & v, DrvInfo & drv,
-    bool ignoreAssertionFailures);
+/* If value `v' denotes a derivation, return a DrvInfo object
+   describing it. Otherwise return nothing. */
+std::experimental::optional<DrvInfo> getDerivation(EvalState & state,
+    Value & v, bool ignoreAssertionFailures);
 
 void getDerivations(EvalState & state, Value & v, const string & pathPrefix,
     Bindings & autoArgs, DrvInfos & drvs,