reflect: inconsistent method indexing between Type.Method and Value.Method

[mdempsky]

From @ianlancetaylor's example in #22053, this program prints "string int" but should print "string string": https://play.golang.org/p/Kw_V41dmX2

Possibly relatedly, this program segfaults when int is replaced by a local named type: https://play.golang.org/p/k45kuWP75S

/cc @crawshaw

[mdempsky]

Hm, this issue doesn't reproduce at master.

Edit: Disregard. I somehow mangled the test file when copying locally.

[mdempsky]

It looks like the issue is Type.Method uses (*rtype).exportedMethods, which filters out unexported methods. However, Value.Method just directly indexes into t.uncommonType().methods().

It seems unfortunate that package reflect needs to filter methods like this anyway. I would think the compiler could just statically partition exported and unexported ones.

[crawshaw]

I believe we need the unexported method data for itabs in the runtime. But you're right that it could be statically partitioned.

[gopherbot]

Change https://golang.org/cl/66770 mentions this issue: reflect: fix method indexing for non-ASCII exported methods

[mdempsky]

@crawshaw Yeah, runtime itab construction and reflect.Implements both need non-exported methods.