* nix-instantiate: return exit status 100 to denote a permanent build

failure.  The build hook can use this to distinguish between
  transient and permanent failures on the remote side.

scripts/build-remote.pl.in

@@ -240,13 +240,13 @@ my $buildFlags = "--max-silent-time $maxSilentTime --fallback --add-root $rootsD
 # work on some platforms when connection sharing is used.)
 pipe STDIN, DUMMY; # make sure we have a readable STDIN
 if (system("ssh $hostName @sshOpts '(read; kill -INT -\$\$) <&0 & nix-store -r $drvPath $buildFlags > /dev/null' 2>&4") != 0) {
-    # If we couldn't run ssh or there was an ssh problem (indicated by
-    # exit code 255), then we return exit code 1; otherwise we assume
-    # that the builder failed, which we indicate to Nix using exit
-    # code 100.  It's important to distinguish between the two because
-    # the first is a transient failure and the latter is permanent.
-    my $res = $? == -1 || ($? >> 8) == 255 ? 1 : 100;
-    print STDERR "build of `$drvPath' on `$hostName' failed with exit code $?\n";
+    # Note that if we get exit code 100 from `nix-store -r', it
+    # denotes a permanent build failure (as opposed to an SSH problem
+    # or a temporary Nix problem).  We propagate this to the caller to
+    # allow it to distinguish between transient and permanent
+    # failures.
+    my $res = $? >> 8;
+    print STDERR "build of `$drvPath' on `$hostName' failed with exit code $res\n";
     removeRoots;
     exit $res;
 }

src/libmain/shared.cc

@@ -393,7 +393,7 @@ int main(int argc, char * * argv)
         printMsg(lvlError, format("error: %1%%2%") % (showTrace ? e.prefix() : "") % e.msg());
         if (e.prefix() != "" && !showTrace)
             printMsg(lvlError, "(use `--show-trace' to show detailed location information)");
-        return 1;
+        return e.status;
     } catch (std::exception & e) {
         printMsg(lvlError, format("error: %1%") % e.what());
         return 1;

src/libstore/build.cc

@@ -214,6 +214,10 @@ public:
 
     bool cacheFailure;
 
+    /* Set if at least one derivation had a BuildError (i.e. permanent
+       failure). */
+    bool permanentFailure;
+
     LocalStore & store;
 
     boost::shared_ptr<HookInstance> hook;
@@ -267,6 +271,7 @@ public:
     /* Wait for input to become available. */
     void waitForInput();
 
+    unsigned int exitStatus();
 };
 
 
@@ -1185,6 +1190,7 @@ void DerivationGoal::tryToBuild()
         if (printBuildTrace)
             printMsg(lvlError, format("@ build-failed %1% %2% %3% %4%")
                 % drvPath % drv.outputs["out"].path % 0 % e.msg());
+        worker.permanentFailure = true;
         amDone(ecFailed);
         return;
     }
@@ -1321,6 +1327,7 @@ void DerivationGoal::buildDone()
             foreach (DerivationOutputs::iterator, i, drv.outputs)
                 worker.store.registerFailedPath(i->second.path);
         
+        worker.permanentFailure = !hookError && !fixedOutput;
         amDone(ecFailed);
         return;
     }
@@ -2444,6 +2451,7 @@ Worker::Worker(LocalStore & store)
     nrLocalBuilds = 0;
     lastWokenUp = 0;
     cacheFailure = queryBoolSetting("build-cache-failure", false);
+    permanentFailure = false;
 }
 
 
@@ -2770,6 +2778,11 @@ void Worker::waitForInput()
 }
 
 
+unsigned int Worker::exitStatus()
+{
+    return permanentFailure ? 100 : 1;
+}
+
 
 //////////////////////////////////////////////////////////////////////
 
@@ -2796,7 +2809,7 @@ void LocalStore::buildDerivations(const PathSet & drvPaths)
         }
             
     if (!failed.empty())
-        throw Error(format("build of %1% failed") % showPaths(failed));
+        throw Error(format("build of %1% failed") % showPaths(failed), worker.exitStatus());
 }
 
 
@@ -2812,7 +2825,7 @@ void LocalStore::ensurePath(const Path & path)
     worker.run(goals);
 
     if (goal->getExitCode() != Goal::ecSuccess)
-        throw Error(format("path `%1%' does not exist and cannot be created") % path);
+        throw Error(format("path `%1%' does not exist and cannot be created") % path, worker.exitStatus());
 }
 
  

src/libutil/types.hh

@@ -29,7 +29,8 @@ protected:
     string prefix_; // used for location traces etc.
     string err;
 public:
-    BaseError(const format & f);
+    unsigned int status; // exit status
+    BaseError(const format & f, unsigned int status = 1);
     ~BaseError() throw () { };
     const char * what() const throw () { return err.c_str(); }
     const string & msg() const throw () { return err; }
@@ -41,7 +42,7 @@ public:
     class newClass : public superClass                  \
     {                                                   \
     public:                                             \
-        newClass(const format & f) : superClass(f) { }; \
+        newClass(const format & f, unsigned int status = 1) : superClass(f, status) { }; \
     };
 
 MakeError(Error, BaseError)

src/libutil/util.cc

@@ -20,7 +20,8 @@ extern char * * environ;
 namespace nix {
 
 
-BaseError::BaseError(const format & f)
+BaseError::BaseError(const format & f, unsigned int status)
+    : status(status)
 {
     err = f.str();
 }