mojom: Add associative arrays to the mojom language.

mojo/public/tools/bindings/pylib/mojom/parse/parser.py

Index: mojo/public/tools/bindings/pylib/mojom/parse/parser.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/parse/parser.py b/mojo/public/tools/bindings/pylib/mojom/parse/parser.py
index 35ac35901e7aa0dd07a0a578646f0f1c9673df52..9ed20eb028cbd21fc5e5d2338151e504d55779de 100644
--- a/mojo/public/tools/bindings/pylib/mojom/parse/parser.py
+++ b/mojo/public/tools/bindings/pylib/mojom/parse/parser.py
@@ -237,6 +237,7 @@ class Parser(object):
     """nonnullable_typename : basictypename
                             | array
                             | fixed_array
+                            | associated_array

[viettrungluu, 2014/09/29 19:34:47]

"associated" -> "associative"

                             | interfacerequest"""
     p[0] = p[1]
 
@@ -275,6 +276,10 @@ class Parser(object):
                        snippet=self._GetSnippet(p.lineno(3)))
     p[0] = p[1] + "[" + p[3] + "]"
 
+  def p_associated_array(self, p):
+    """associated_array : typename LBRACKET basictypename RBRACKET"""

[viettrungluu, 2014/09/29 19:34:47]

a) It seems dubious/incorrect to allow "handletypes" as keys.
b) I'm not sure about the syntax, but note that the grammar is dubious and
parses things "backwards"[*], which is unfortunate. (This is an existing
problem, even with arrays.)
c) Allowing even arbitrary identifiers but not handletypes for keys is probably
not what you want. This allows structs as keys, which may then contain handles.
(Of course, not allowing arbitrary-ish things may preclude allowing strings.)

[*] E.g., the type of "string foo[int32][double];" is parsed as double -> (int32
-> string), whereas you probably want it to mean int32 -> (double -> string).

[yzshen1, 2014/09/29 19:53:24]

About the "backward" issue, I am not sure whether changing it will make other
things less clear. For example:

string[int][handle]?

The trailing '?' means "the whole thing is nullable", which seems natural to
associate with the outermost array.

[Elliot Glaysher, 2014/10/02 19:54:03]

Fixed by changing the grammar to look for "identifier".
This is large and thorny enough that I'm not going to deal with it in the
general case. I've fixed this in translate.py for the specific case of
associative arrays.

The actual fix to this is "rewrite the mojom compiler".
Fixed this by adding type checks at a later phase once we have typing
information.

+    p[0] = p[1] + "{" + p[3] + "}"
+
   def p_interfacerequest(self, p):
     """interfacerequest : identifier AMP"""
     p[0] = p[1] + "&"