From 5c7520b56919393adceff57387e828c6a7ec4b85 Mon Sep 17 00:00:00 2001
From: Shea Levy <shea@shealevy.com>
Date: Tue, 15 May 2012 23:00:23 -0400
Subject: [PATCH 1/2] prim_import: Don't build derivations in read-only mode

---
 src/libexpr/primops.cc | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index d3809e6984a..8f6e5fabf99 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -49,20 +49,29 @@ static void prim_import(EvalState & state, Value * * args, Value & v)
         if (!store->isValidPath(ctx))
             throw EvalError(format("cannot import `%1%', since path `%2%' is not valid")
                 % path % ctx);
-        if (isDerivation(ctx))
-            try {
-                /* For performance, prefetch all substitute info. */
-                PathSet willBuild, willSubstitute, unknown;
-                unsigned long long downloadSize, narSize;
-                queryMissing(*store, singleton<PathSet>(ctx),
-                    willBuild, willSubstitute, unknown, downloadSize, narSize);
+        if (isDerivation(ctx)) {
+            string outputName = decodeContext(*i).second;
+            Derivation drv = derivationFromPath(*store, ctx);
+
+            if (!store->isValidPath(drv.outputs[outputName].path)) {
+                if (settings.readOnlyMode)
+                    throw ImportError(format("cannot import `%1%', since output `%2%' of derivation `%3%' is not valid")
+                        % path % outputName % ctx);
+                try {
+                    /* For performance, prefetch all substitute info. */
+                    PathSet willBuild, willSubstitute, unknown;
+                    unsigned long long downloadSize, narSize;
+                    queryMissing(*store, singleton<PathSet>(ctx),
+                        willBuild, willSubstitute, unknown, downloadSize, narSize);
                   
-                /* !!! If using a substitute, we only need to fetch
-                   the selected output of this derivation. */
-                store->buildPaths(singleton<PathSet>(ctx));
-            } catch (Error & e) {
-                throw ImportError(e.msg());
+                    /* !!! If using a substitute, we only need to fetch
+                       the selected output of this derivation. */
+                    store->buildPaths(singleton<PathSet>(ctx));
+                } catch (Error & e) {
+                    throw ImportError(e.msg());
+                }
             }
+        }
     }
 
     if (isStorePath(path) && store->isValidPath(path) && isDerivation(path)) {

From 9e0561bd8fbc963ce31f19bd0a060dd9aac1cebf Mon Sep 17 00:00:00 2001
From: Shea Levy <shea@shealevy.com>
Date: Wed, 29 Aug 2012 00:11:12 -0400
Subject: [PATCH 2/2] prim_import: Distinguish between failures due to
 read-only mode and other failures

---
 src/libexpr/nixexpr.hh |  1 +
 src/libexpr/primops.cc | 22 +++++++++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index bc6c3287c79..0eac3d69d88 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -16,6 +16,7 @@ MakeError(ThrownError, AssertionError)
 MakeError(Abort, EvalError)
 MakeError(TypeError, EvalError)
 MakeError(ImportError, EvalError) // error building an imported derivation
+MakeError(ImportReadOnlyError, EvalError) // error when trying to import a derivation in read-only mode
 
 
 /* Position objects. */
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 8f6e5fabf99..7189465af93 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -45,18 +45,26 @@ static void prim_import(EvalState & state, Value * * args, Value & v)
 
     foreach (PathSet::iterator, i, context) {
         Path ctx = decodeContext(*i).first;
+        string outputName = decodeContext(*i).second;
         assert(isStorePath(ctx));
-        if (!store->isValidPath(ctx))
-            throw EvalError(format("cannot import `%1%', since path `%2%' is not valid")
-                % path % ctx);
+        if (!store->isValidPath(ctx)) {
+            if (outputName.empty())
+                throw EvalError(format("cannot import `%1%', since path `%2%' is not valid")
+                    % path % ctx);
+            else
+                throw ImportReadOnlyError(format("cannot import `%1%', since path `%2%' cannot be written to the store in read-only mode")
+                    % path % ctx);
+        }
         if (isDerivation(ctx)) {
-            string outputName = decodeContext(*i).second;
             Derivation drv = derivationFromPath(*store, ctx);
 
-            if (!store->isValidPath(drv.outputs[outputName].path)) {
+            if (outputName.empty() ||
+                    !store->isValidPath(drv.outputs[outputName].path)) {
                 if (settings.readOnlyMode)
-                    throw ImportError(format("cannot import `%1%', since output `%2%' of derivation `%3%' is not valid")
-                        % path % outputName % ctx);
+                    foreach (DerivationOutputs::iterator, j, drv.outputs)
+                        if (!store->isValidPath(j->second.path))
+                            throw ImportReadOnlyError(format("cannot import `%1%', since derivation `%2%' cannot be realised in read-only mode")
+                                % path % ctx);
                 try {
                     /* For performance, prefetch all substitute info. */
                     PathSet willBuild, willSubstitute, unknown;