Add a bit of graceful error handling to C++ IDL code

Instead of failing obtusely, do some checking of the JSON schema so we
can produce useful error messages. This doesn't strictly check
everything that could be checked, but it will catch the most common
errors (i.e. the ones I discovered while making this change originally).

hphp/tools/gen-ext-hhvm/gen-ext-hhvm.cpp

@@ -576,12 +576,9 @@ void processSymbol(const fbstring& symbol, std::ostream& header,
   cpp << in << "int32_t count = ar->numArgs();\n";
   cpp << in << "TypedValue* args UNUSED = ((TypedValue*)ar) - 1;\n";
 
-  if (func.isMethod()) {
+  if (func.isMethod() && !func.isStatic) {
     cpp << in
         << "ObjectData* this_ = (ar->hasThis() ? ar->getThis() : nullptr);\n";
-  }
-
-  if (func.isMethod() && !func.isStatic) {
     cpp << in << "if (this_) {\n";
     in -= 2;
   }
@@ -685,6 +682,7 @@ int main(int argc, const char* argv[]) {
       parseIDL(argv[i], funcs, classes);
     } catch (const std::exception& exc) {
       std::cerr << argv[i] << ": " << exc.what() << "\n";
+      return 1;
     }
   }
 

hphp/tools/gen-ext-hhvm/gen-infotabs.cpp

@@ -43,6 +43,7 @@ int main(int argc, const char* argv[]) {
       parseIDL(argv[i], funcs, classes);
     } catch (const std::exception& exc) {
       std::cerr << argv[i] << ": " << exc.what() << "\n";
+      return 1;
     }
   }
 

hphp/tools/gen-ext-hhvm/idl.cpp

@@ -20,6 +20,7 @@
 #include <unordered_map>
 #include <unordered_set>
 
+#include "folly/Format.h"
 #include "folly/json.h"
 
 
@@ -99,8 +100,28 @@ bool PhpParam::defValNeedsVariable() const {
 
 PhpFunc PhpFunc::fromDynamic(const folly::dynamic& d,
                              const fbstring& className) {
-  auto refIt = d.find("ref");
-  bool ref = (refIt != d.items().end() && refIt->second.asString() == "true");
+  // Better at least have a name
+  auto name = d["name"].asString();
+  auto args = d.find("args");
+  auto flags = d.find("flags");
+  auto ret = d.find("return");
+  if (args == d.items().end() || !args->second.isArray()) {
+    throw std::logic_error(
+      folly::format("'{0}' must have an array field 'args'", name).str()
+    );
+  }
+  if (flags == d.items().end() || !flags->second.isArray()) {
+    throw std::logic_error(
+      folly::format("'{0}' must have an array field 'flags'", name).str()
+    );
+  }
+  if (ret == d.items().end() || !ret->second.isObject() ||
+      ret->second.find("type") == ret->second.items().end()) {
+    throw std::logic_error(
+      folly::format("'{0}' must have an array field 'return', which must have "
+                    "a string field 'type'", name).str()
+    );
+  }
 
   auto areVarargs = [](const fbstring& str) {
     return (str == "VariableArguments" ||
@@ -108,8 +129,15 @@ PhpFunc PhpFunc::fromDynamic(const folly::dynamic& d,
             str == "MixedVariableArguments");
   };
 
-  auto name = d["name"].asString();
-  auto params = folly::convertTo<fbvector<PhpParam>>(d["args"]);
+  fbvector<PhpParam> params;
+  try {
+    params = std::move(folly::convertTo<fbvector<PhpParam>>(args->second));
+  } catch (const std::exception& exc) {
+    throw std::logic_error(
+      folly::format("'{0}' has an arg with either 'name' or 'type' field "
+                    "missing", name).str()
+    );
+  }
   if (name == "__get" ||
       name == "__set" ||
       name == "__isset" ||
@@ -120,24 +148,27 @@ PhpFunc PhpFunc::fromDynamic(const folly::dynamic& d,
     }
   }
 
-  PhpFunc ret;
-  ret.name = name;
-  ret.className = className;
-  ret.returnCppType = typeString(d["return"]["type"], true);
-  ret.returnByRef = ref;
-  ret.params = params;
-  ret.isVarargs = anyFlags(areVarargs, d["flags"]);
-  ret.isStatic = false;
+  auto refIt = d.find("ref");
+  bool ref = (refIt != d.items().end() && refIt->second.asString() == "true");
+
+  PhpFunc retval;
+  retval.name = name;
+  retval.className = className;
+  retval.returnCppType = typeString(ret->second["type"], true);
+  retval.returnByRef = ref;
+  retval.params = params;
+  retval.isVarargs = anyFlags(areVarargs, flags->second);
+  retval.isStatic = false;
 
   if (!className.empty()) {
     auto areStatic = [](const fbstring& str) {
       return str == "IsStatic";
     };
 
-    ret.isStatic = anyFlags(areStatic, d["flags"]);
+    retval.isStatic = anyFlags(areStatic, flags->second);
   }
-  ret.initComputedProps();
-  return ret;
+  retval.initComputedProps();
+  return retval;
 }
 
 void PhpFunc::initComputedProps() {