From dda9c1cc6e10b554c4eaa8325a2ff9f2cae19626 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Sun, 21 Oct 2018 01:33:40 +0200
Subject: [PATCH] ir: fix interface call edge case

A function on a type that is put in an interface must not be assumed to
not need a context pointer when it isn't directly put in a function
pointer, because the interface call side won't know this and pass an
extra parameter with that extra function pointer.

This is usually not a problem but WebAssembly has strict checks on
function signatures so this resulted in an error when running
src/examples/test/test.go.
---
 ir/passes.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/ir/passes.go b/ir/passes.go
index 9955658f..46133a10 100644
--- a/ir/passes.go
+++ b/ir/passes.go
@@ -416,6 +416,12 @@ func (p *Program) AllInterfaces() []*Interface {
 
 func (p *Program) FunctionNeedsContext(f *Function) bool {
 	if !f.addressTaken {
+		if f.Signature.Recv() != nil {
+			_, hasInterfaceConversion := p.TypeNum(f.Signature.Recv().Type())
+			if hasInterfaceConversion && p.SignatureNeedsContext(f.Signature) {
+				return true
+			}
+		}
 		return false
 	}
 	return p.SignatureNeedsContext(f.Signature)