This is unrelated to the new parser; the same error appears with the old parser:
go tool compile -oldparser foo.go

Slightly simpler repro:

package b

var (
    x uint
    y = x
    z = uintptr(y)
)

The problem is when staticassign is looking at the "z = uintptr(y)" node, it strips the OCONVNOP, finds the ONAME node for y, and then calls staticcopy(z, y, out).

staticcopy(z, y, out) reaches the case ONAME, recursively calls staticcopy(z, x, out) which returns false (because x's Defn is nil), and then synthesizes a "z = x" assignment, which later fails typechecking.

One fix seems to be to reinsert OCONVNOP nodes as necessary when generating that OAS node.

This bug no longer seems to be an issue on Go1.6.2 at least. See https://play.golang.org/p/4GCc3_5qoT

or inlined

package main

import (
    "fmt"
    "runtime"
)

func f1() {
    var (
        w []*uint
        x = *w[0]
        y = x
        z = (uintptr)(y)
    )
    fmt.Printf("z: %v\n", z)
}

func f2() {
    var (
        x uint
        y = x
        z = uintptr(y)
    )
    fmt.Printf("z: %v\n", z)
}

func main() {
    fmt.Printf("Version: %s\n", runtime.Version())
}

Still an issue with 1.7.

@griesemer I am running Version: devel +7e45516 Sat Nov 26 05:01:32 2016 +0000 and the test program in #13263 (comment) compiles alright. Would you mind double checking?

Actually you are right(I stand corrected): with @dvyukov's test program with the global declarations it fails to compile but when I put them in functions, it compiles correctly.

CL https://golang.org/cl/33900 mentions this issue.

Reported offline by @cherrymui in my CL https://golang.org/cl/33900, the problem seems broader
and not only from uint to uintptr in global declarations, but also in uint to uint64.

package a

var (
	a uint
	b = a
	c = (uint64)(b)
)

CL https://golang.org/cl/33970 mentions this issue.