Bug 921563 - part 1 - declare return types in IPDL C++ with C++0x late return syntax; r=gps

Every IPDL C++ class contains a bunch of typedefs.

Every IPDL C++ source file contains a bunch of typedefs and using statements
for the exact same types.

Why is that?

Because the class itself is not in scope for name lookup of return types of C++
methods.  This limitation is annoying, but it makes sense.  The typedefs and
using statements therefore exist so we can be a little sloppy about return
types.

Let's stop being sloppy and polluting the global namespace inside these
files.  Less pollution makes it easier to smash the IPDL files together for
unified compilation.  One could do this by qualifying all necessary return
types...or we could just use the C++0x late return syntax, which guarantees the
class *is* in scope for name lookup.  I like this version a lot better.

ipc/ipdl/ipdl/cxx/ast.py

@@ -478,6 +478,7 @@ class MethodDecl(Node):
         self.never_inline = never_inline # bool
         self.typeop = typeop            # Type or None
         self.T = T                      # Type or None
+        self.only_for_definition = False
 
     def __deepcopy__(self, memo):
         return MethodDecl(

ipc/ipdl/ipdl/cxx/cgen.py

@@ -189,6 +189,9 @@ class CxxCodeGen(CodePrinter, Visitor):
         if md.virtual:
             self.write('virtual ')
         if md.ret:
+            if md.only_for_definition:
+                self.write('auto ')
+            else:
                 md.ret.accept(self)
                 self.println()
                 self.printdent()
@@ -204,6 +207,9 @@ class CxxCodeGen(CodePrinter, Visitor):
 
         if md.const:
             self.write(' const')
+        if md.ret and md.only_for_definition:
+            self.write(' -> ')
+            md.ret.accept(self)
         if md.warn_unused:
             self.write(' NS_WARN_UNUSED_RESULT')
         if md.pure:

ipc/ipdl/ipdl/lower.py

@@ -5316,6 +5316,7 @@ def _splitMethodDefn(md, clsname):
     md.decl.static = 0
     md.decl.warn_unused = 0
     md.decl.never_inline = 0
+    md.decl.only_for_definition = True
     for param in md.decl.params:
         if isinstance(param, Param):
             param.default = None