toJSON: Add attribute path to trace

NixOS · Jul 31, 2023 · f3987b3 · f3987b3
1 parent 2d1d811
commit f3987b3
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Showing 3 changed files with 86 additions and 3 deletions.
diff --git a/src/libexpr/value-to-json.cc b/src/libexpr/value-to-json.cc
@@ -43,6 +43,7 @@ json printValueAsJSON(EvalState & state, bool strict,
             break;
 
         case nNull:
+            // already initialized as null
             break;
 
         case nAttrs: {
@@ -59,7 +60,13 @@ json printValueAsJSON(EvalState & state, bool strict,
                     names.emplace(state.symbols[j.name]);
                 for (auto & j : names) {
                     Attr & a(*v.attrs->find(state.symbols.create(j)));
-                    out[j] = printValueAsJSON(state, strict, *a.value, a.pos, context, copyToStore);
+                    try {
+                        out[j] = printValueAsJSON(state, strict, *a.value, a.pos, context, copyToStore);
+                    } catch (Error & e) {
+                        e.addTrace(state.positions[a.pos],
+                            hintfmt("while evaluating attribute '%1%'", j));
+                        throw;
+                    }
                 }
             } else
                 return printValueAsJSON(state, strict, *i->value, i->pos, context, copyToStore);
@@ -68,8 +75,17 @@ json printValueAsJSON(EvalState & state, bool strict,
 
         case nList: {
             out = json::array();
-            for (auto elem : v.listItems())
-                out.push_back(printValueAsJSON(state, strict, *elem, pos, context, copyToStore));
+            int i = 0;
+            for (auto elem : v.listItems()) {
+                try {
+                    out.push_back(printValueAsJSON(state, strict, *elem, pos, context, copyToStore));
+                } catch (Error & e) {
+                    e.addTrace({},
+                        hintfmt("while evaluating list element %1%", i));
+                    throw;
+                }
+                i++;
+            }
             break;
         }
 

diff --git a/tests/lang/eval-fail-toJSON.err.exp b/tests/lang/eval-fail-toJSON.err.exp
@@ -0,0 +1,57 @@
+error:
+       … while calling the 'toJSON' builtin
+
+         at /pwd/lang/eval-fail-toJSON.nix:1:1:
+
+            1| builtins.toJSON {
+             | ^
+            2|   a.b = [
+
+       … while evaluating attribute 'a'
+
+         at /pwd/lang/eval-fail-toJSON.nix:2:3:
+
+            1| builtins.toJSON {
+            2|   a.b = [
+             |   ^
+            3|     true
+
+       … while evaluating attribute 'b'
+
+         at /pwd/lang/eval-fail-toJSON.nix:2:3:
+
+            1| builtins.toJSON {
+            2|   a.b = [
+             |   ^
+            3|     true
+
+       … while evaluating list element 3
+
+       … while evaluating attribute 'c'
+
+         at /pwd/lang/eval-fail-toJSON.nix:7:7:
+
+            6|     {
+            7|       c.d = throw "hah no";
+             |       ^
+            8|     }
+
+       … while evaluating attribute 'd'
+
+         at /pwd/lang/eval-fail-toJSON.nix:7:7:
+
+            6|     {
+            7|       c.d = throw "hah no";
+             |       ^
+            8|     }
+
+       … while calling the 'throw' builtin
+
+         at /pwd/lang/eval-fail-toJSON.nix:7:13:
+
+            6|     {
+            7|       c.d = throw "hah no";
+             |             ^
+            8|     }
+
+       error: hah no
diff --git a/tests/lang/eval-fail-toJSON.nix b/tests/lang/eval-fail-toJSON.nix
@@ -0,0 +1,10 @@
+builtins.toJSON {
+  a.b = [
+    true
+    false
+    "it's a bird"
+    {
+      c.d = throw "hah no";
+    }
+  ];
+}