[YAMLIO] Add the ability to map with context.

mapping a yaml field to an object in code has always been
a stateless operation.  You could still pass state by using the
`setContext` function of the YAMLIO object, but this represented
global state for the entire yaml input.  In order to have
context-sensitive state, it is necessary to pass this state in
at the granularity of an individual mapping.

This patch adds support for this type of context-sensitive state.
You simply pass an additional argument of type T to the
`mapRequired` or `mapOptional` functions, and provided you have
specialized a `MappingContextTraits<U, T>` class with the
appropriate mapping function, you can pass this context into
the mapping function.

Reviewed By: chandlerc
Differential Revision: https://reviews.llvm.org/D24162

llvm-svn: 280977

1 files changed, 69 insertions, 0 deletions

diff --git a/llvm/unittests/Support/YAMLIOTest.cpp b/llvm/unittests/Support/YAMLIOTest.cpp
index 5f35a802caa..bf70e749b4f 100644
--- a/llvm/unittests/Support/YAMLIOTest.cpp
+++ b/llvm/unittests/Support/YAMLIOTest.cpp
@@ -2299,3 +2299,72 @@ TEST(YAMLIO, TestWrapFlow) {
     out.clear();
   }
 }
+
+struct MappingContext {
+  int A = 0;
+};
+struct SimpleMap {
+  int B = 0;
+  int C = 0;
+};
+
+struct NestedMap {
+  NestedMap(MappingContext &Context) : Context(Context) {}
+  SimpleMap Simple;
+  MappingContext &Context;
+};
+
+namespace llvm {
+namespace yaml {
+template <> struct MappingContextTraits<SimpleMap, MappingContext> {
+  static void mapping(IO &io, SimpleMap &sm, MappingContext &Context) {
+    io.mapRequired("B", sm.B);
+    io.mapRequired("C", sm.C);
+    ++Context.A;
+    io.mapRequired("Context", Context.A);
+  }
+};
+
+template <> struct MappingTraits<NestedMap> {
+  static void mapping(IO &io, NestedMap &nm) {
+    io.mapRequired("Simple", nm.Simple, nm.Context);
+  }
+};
+}
+}
+
+TEST(YAMLIO, TestMapWithContext) {
+  MappingContext Context;
+  NestedMap Nested(Context);
+  std::string out;
+  llvm::raw_string_ostream ostr(out);
+
+  Output yout(ostr, nullptr, 15);
+
+  yout << Nested;
+  ostr.flush();
+  EXPECT_EQ(1, Context.A);
+  EXPECT_EQ("---\n"
+            "Simple:          \n"
+            "  B:               0\n"
+            "  C:               0\n"
+            "  Context:         1\n"
+            "...\n",
+            out);
+
+  out.clear();
+
+  Nested.Simple.B = 2;
+  Nested.Simple.C = 3;
+  yout << Nested;
+  ostr.flush();
+  EXPECT_EQ(2, Context.A);
+  EXPECT_EQ("---\n"
+            "Simple:          \n"
+            "  B:               2\n"
+            "  C:               3\n"
+            "  Context:         2\n"
+            "...\n",
+            out);
+  out.clear();
+}