From e255be6cbef4b02185fb09218aab3daf59bcfa4c Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 14 May 2024 17:31:06 +0200
Subject: [PATCH] builtins.toPath: Rewrite virtual paths

---
 src/libexpr/eval.hh    |  5 ++++-
 src/libexpr/paths.cc   |  4 ++--
 src/libexpr/primops.cc | 10 +++++++++-
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index d853cbc4592..62fad7d8d83 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -372,7 +372,10 @@ public:
        materializing those store paths. This is a backward
        compatibility hack to make buggy derivation attributes like
        `tostring ./bla` produce the same evaluation result. */
-    std::string rewriteVirtualPaths(std::string_view s, PosIdx pos);
+    std::string rewriteVirtualPaths(
+        std::string_view s,
+        std::string_view warning,
+        PosIdx pos);
 
     /* Replace all virtual paths (i.e. `/nix/store/lazylazy...`) in a
        string by a pretty-printed rendition of the corresponding input
diff --git a/src/libexpr/paths.cc b/src/libexpr/paths.cc
index b3b9aa1d03b..7a9003a5365 100644
--- a/src/libexpr/paths.cc
+++ b/src/libexpr/paths.cc
@@ -91,7 +91,7 @@ std::string EvalState::prettyPrintPaths(std::string_view s)
     }
 }
 
-std::string EvalState::rewriteVirtualPaths(std::string_view s, PosIdx pos)
+std::string EvalState::rewriteVirtualPaths(std::string_view s, std::string_view warning, PosIdx pos)
 {
     std::string res;
 
@@ -120,7 +120,7 @@ std::string EvalState::rewriteVirtualPaths(std::string_view s, PosIdx pos)
             assert(accessor != sourceAccessors.end()); // FIXME
 
             warn(
-                "derivation at %s has an attribute that refers to source tree '%s' without context; this does not work correctly",
+                std::string(warning), // FIXME: should accept a string_view
                 positions[pos], accessor->second->showPath(CanonPath::root));
 
             // FIXME: cache this.
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 9c734c013d7..767da61497e 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1352,7 +1352,10 @@ static void derivationStrictInternal(
        don't have a context, so aren't accessible from a sandbox) but
        we don't want to change evaluation results.  */
     for (auto & [name, value] : drv.env)
-        value = state.rewriteVirtualPaths(value, pos);
+        value = state.rewriteVirtualPaths(
+            value,
+            "derivation at %s has an attribute that refers to source tree '%s' without context; this does not work correctly",
+            pos);
 
     /* Do we have all required attributes? */
     if (drv.builder == "")
@@ -2170,6 +2173,11 @@ static void prim_toFile(EvalState & state, const PosIdx pos, Value * * args, Val
     std::string name(state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.toFile"));
     std::string contents(state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.toFile"));
 
+    contents = state.rewriteVirtualPaths(
+        contents,
+        "call to `builtins.toFile` at %s refers to source tree '%s' without context; this does not work correctly",
+        pos);
+
     StorePathSet refs;
 
     for (auto c : context) {