From 8479549ad471bfd642e228808691835ce7b8b1c1 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Mon, 12 Sep 2022 06:34:25 -0700
Subject: [PATCH 1/2] Special-case empty `{ ... }` sequences for prettier name
 mangling.

With the current mangling for eg. records:

```python
  return 'record { ' + ', '.join(mangled_fields) + ' }'
```

the mangling for a record with 0 fields is `record {  }`, with two
spaces between the braces. That looks subjectively surprising.

This PR adds special cases to the mangling for `record` and similar
types so that the mangling is `record {}`, with no spaces between the
braces, which is subjectively prettier.

The argument against this is that empty records should be very rare,
so prettiness isn't important, and every special case makes the system
more complex. The argument for it is that a mangling with two spaces
looks weird.
---
 design/mvp/canonical-abi/definitions.py | 33 ++++++++++++++++++-------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/design/mvp/canonical-abi/definitions.py b/design/mvp/canonical-abi/definitions.py
index 4701db70..d62da6fd 100644
--- a/design/mvp/canonical-abi/definitions.py
+++ b/design/mvp/canonical-abi/definitions.py
@@ -1145,26 +1145,41 @@ def mangle_valtype(t):
 
 def mangle_recordtype(fields):
   mangled_fields = (f.label + ': ' + mangle_valtype(f.t) for f in fields)
-  return 'record { ' + ', '.join(mangled_fields) + ' }'
+  if len(mangled_fields) == 0:
+    return 'record {}'
+  else:
+    return 'record { ' + ', '.join(mangled_fields) + ' }'
 
 def mangle_tupletype(ts):
   return 'tuple<' + ', '.join(mangle_valtype(t) for t in ts) + '>'
 
 def mangle_flags(labels):
-  return 'flags { ' + ', '.join(labels) + ' }'
+  if len(labels) == 0:
+    return 'flags {}'
+  else:
+    return 'flags { ' + ', '.join(labels) + ' }'
 
 def mangle_varianttype(cases):
-  mangled_cases = ('{label}{payload}'.format(
-                     label = c.label,
-                     payload = '' if c.t is None else '(' + mangle_valtype(c.t) + ')')
-                   for c in cases)
-  return 'variant { ' + ', '.join(mangled_cases) + ' }'
+  if len(cases) == 0:
+    return 'variant {}'
+  else:
+    mangled_cases = ('{label}{payload}'.format(
+                       label = c.label,
+                       payload = '' if c.t is None else '(' + mangle_valtype(c.t) + ')')
+                     for c in cases)
+    return 'variant { ' + ', '.join(mangled_cases) + ' }'
 
 def mangle_enumtype(labels):
-  return 'enum { ' + ', '.join(labels) + ' }'
+  if len(labels) == 0:
+    return 'enum {}'
+  else:
+    return 'enum { ' + ', '.join(labels) + ' }'
 
 def mangle_uniontype(ts):
-  return 'union { ' + ', '.join(mangle_valtype(t) for t in ts) + ' }'
+  if len(ts) == 0:
+    return 'union {}'
+  else:
+    return 'union { ' + ', '.join(mangle_valtype(t) for t in ts) + ' }'
 
 def mangle_optiontype(t):
   return 'option<' + mangle_valtype(t) + '>'

From 4fd13dddb63494a32e3a2e805048ac05ec807506 Mon Sep 17 00:00:00 2001
From: Dan Gohman <dev@sunfishcode.online>
Date: Mon, 12 Sep 2022 07:00:08 -0700
Subject: [PATCH 2/2] Don't check the len of a generator.

---
 design/mvp/canonical-abi/definitions.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/design/mvp/canonical-abi/definitions.py b/design/mvp/canonical-abi/definitions.py
index d62da6fd..8bc4011f 100644
--- a/design/mvp/canonical-abi/definitions.py
+++ b/design/mvp/canonical-abi/definitions.py
@@ -1144,10 +1144,10 @@ def mangle_valtype(t):
     case Result(ok,error) : return mangle_resulttype(ok,error)
 
 def mangle_recordtype(fields):
-  mangled_fields = (f.label + ': ' + mangle_valtype(f.t) for f in fields)
-  if len(mangled_fields) == 0:
+  if len(fields) == 0:
     return 'record {}'
   else:
+    mangled_fields = (f.label + ': ' + mangle_valtype(f.t) for f in fields)
     return 'record { ' + ', '.join(mangled_fields) + ' }'
 
 def mangle_tupletype(ts):