Set environment variables for .attrs.json & .attrs.sh

This way no derivation has to expect that these files are in the `cwd`
during the build. This is problematic for `nix-shell` where these files
would have to be inserted into the nix-shell's `cwd` which can become
problematic with e.g. recursive `nix-shell`.

To remain backwards-compatible, the location inside the build sandbox
will be kept, however using these files directly should be deprecated
from now on.

src/libstore/build/local-derivation-goal.cc

@@ -1093,8 +1093,10 @@ void LocalDerivationGoal::writeStructuredAttrs()
 
         writeFile(tmpDir + "/.attrs.sh", rewriteStrings(jsonSh, inputRewrites));
         chownToBuilder(tmpDir + "/.attrs.sh");
+        env["ATTRS_SH_FILE"] = tmpDir + "/.attrs.sh";
         writeFile(tmpDir + "/.attrs.json", rewriteStrings(json.dump(), inputRewrites));
         chownToBuilder(tmpDir + "/.attrs.json");
+        env["ATTRS_JSON_FILE"] = tmpDir + "/.attrs.json";
     }
 }
 

src/nix-build/nix-build.cc

@@ -428,7 +428,6 @@ static void main_nix_build(int argc, char * * argv)
                 env[var.first] = var.second;
 
         std::string structuredAttrsRC;
-        std::string exitCmd;
 
         if (env.count("__json")) {
             StorePathSet inputs;
@@ -448,11 +447,13 @@ static void main_nix_build(int argc, char * * argv)
             if (auto structAttrs = parsedDrv.generateStructuredAttrs(std::nullopt, *store, inputs)) {
                 auto val = structAttrs.value();
                 structuredAttrsRC = val.first;
-                auto attrsJSON = std::filesystem::current_path().string() + "/.attrs.json";
+                auto attrsJSON = (Path) tmpDir + "/.attrs.json";
                 writeFile(attrsJSON, val.second.dump());
-                exitCmd = "\n_rm_attrs_json() { rm -f " + attrsJSON + "; }"
-                    + "\nexitHooks+=(_rm_attrs_json)"
-                    + "\nfailureHooks+=(_rm_attrs_json)\n";
+                auto attrsSH = (Path) tmpDir + "/.attrs.sh";
+                writeFile(attrsSH, val.first);
+                env["ATTRS_SH_FILE"] = attrsSH;
+                env["ATTRS_JSON_FILE"] = attrsJSON;
+                keepTmp = true;
             }
         }
 
@@ -471,7 +472,7 @@ static void main_nix_build(int argc, char * * argv)
                 (pure ? "" : "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc;") +
                 "%2%"
                 "dontAddDisableDepTrack=1;\n"
-                + structuredAttrsRC + exitCmd +
+                + structuredAttrsRC +
                 "\n[ -e $stdenv/setup ] && source $stdenv/setup; "
                 "%3%"
                 "PATH=%4%:\"$PATH\"; "

tests/structured-attrs.nix

@@ -36,7 +36,7 @@ mkDerivation {
     echo bar > $dest
     echo foo > $dest2
 
-    json=$(cat .attrs.json)
+    json=$(cat $ATTRS_JSON_FILE)
     [[ $json =~ '"narHash":"sha256:1r7yc43zqnzl5b0als5vnyp649gk17i37s7mj00xr8kc47rjcybk"' ]]
     [[ $json =~ '"narSize":288' ]]
     [[ $json =~ '"closureSize":288' ]]

tests/structured-attrs.sh

@@ -10,7 +10,5 @@ nix-build structured-attrs.nix -A all -o $TEST_ROOT/result
 [[ $(cat $TEST_ROOT/result-dev/foo) = foo ]]
 
 export NIX_BUILD_SHELL=$SHELL
-[[ ! -e '.attrs.json' ]]
 env NIX_PATH=nixpkgs=shell.nix nix-shell structured-attrs-shell.nix \
-    --run 'test -e .attrs.json; test "3" = "$(jq ".my.list|length" < .attrs.json)"'
-[[ ! -e '.attrs.json' ]]
+    --run 'test -e .attrs.json; test "3" = "$(jq ".my.list|length" < $ATTRS_JSON_FILE)"'