Adds ResultNames to HostFunctionBuilder and FunctionDefinition (#887)

This adds ResultNames to HostFunctionBuilder and FunctionDefinition
which helps for multi-results or special-cased ones.

End users can access result names in `FunctionDefinition.ResultNames` or
set for their own host functions via
`HostFunctionBuilder.WithResultNames`. This change adds them for all
built-in functions where result names help.

Most notably, GOOS=js uses `ProxyFunc` to allow logging when a function
returns multiple results. Before, the results were returned without
names: e.g. `11231,1` and now they are named like `n=11231,ok=1`.

We soon plan to allow more visibility in WASI, for example, logging
results that will write to memory offsets. This infrastructure makes it
possible to do that.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

builder_test.go

@@ -89,6 +89,29 @@ func TestNewHostModuleBuilder_Compile(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "WithFunc WithName WithResultNames",
+			input: func(r Runtime) HostModuleBuilder {
+				return r.NewHostModuleBuilder("").NewFunctionBuilder().
+					WithFunc(uint32_uint32).
+					WithName("get").WithResultNames("x").
+					Export("1")
+			},
+			expected: &wasm.Module{
+				TypeSection: []*wasm.FunctionType{
+					{Params: []api.ValueType{i32}, Results: []api.ValueType{i32}},
+				},
+				FunctionSection: []wasm.Index{0},
+				CodeSection:     []*wasm.Code{wasm.MustParseGoReflectFuncCode(uint32_uint32)},
+				ExportSection: []*wasm.Export{
+					{Name: "1", Type: wasm.ExternTypeFunc, Index: 0},
+				},
+				NameSection: &wasm.NameSection{
+					FunctionNames: wasm.NameMap{{Index: 0, Name: "get"}},
+					ResultNames:   []*wasm.NameMapAssoc{{Index: 0, NameMap: wasm.NameMap{{Index: 0, Name: "x"}}}},
+				},
+			},
+		},
 		{
 			name: "WithFunc overwrites existing",
 			input: func(r Runtime) HostModuleBuilder {