[PATCH] D39908: Allow empty mappings for optional YAML input

[Dave Lee via Phabricator via llvm-commits]

kastiglione created this revision.

This change fixes a bug where `obj2yaml` can in some cases produce YAML that
causes `yaml2obj` to error.

The ELF YAML document structure has a `Sections` mapping, which contains three
mappings, all of which are optional: `Local`, `Global`, and `Weak.` Any one of
these can be missing, but if all three are missing, then `yaml2obj` errors. This
change allows YAML input for cases like this one.

This caused test failures while working on https://reviews.llvm.org/D39582, which introduces a
`DynamicaSymbols` mapping.


https://reviews.llvm.org/D39908

Files:
  lib/Support/YAMLTraits.cpp
  test/tools/yaml2obj/empty-symbols.yaml


Index: test/tools/yaml2obj/empty-symbols.yaml
===================================================================
--- /dev/null
+++ test/tools/yaml2obj/empty-symbols.yaml
@@ -0,0 +1,10 @@
+# Ensure yaml2obj doesn't error on empty optional mappings, such as Symbols
+# RUN: yaml2obj %s -o %t
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+Symbols:
Index: lib/Support/YAMLTraits.cpp
===================================================================
--- lib/Support/YAMLTraits.cpp
+++ lib/Support/YAMLTraits.cpp
@@ -160,7 +160,9 @@
 
   MapHNode *MN = dyn_cast<MapHNode>(CurrentNode);
   if (!MN) {
-    setError(CurrentNode, "not a mapping");
+    bool OptionalNode = !Required && isa<EmptyHNode>(CurrentNode);
+    if (!OptionalNode)
+      setError(CurrentNode, "not a mapping");
     return false;
   }
   MN->ValidKeys.push_back(Key);


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