proc: make structMember work on pointer Variables created through cast

When casting an integer into a struct pointer we make a fake pointer
variable that doesn't have an address, maybeDereference and
structMember should still work on this kind of Variable.

Fixes #1432

_fixtures/issue1432.go

@@ -0,0 +1,16 @@
+package main
+
+import "runtime"
+
+type s struct {
+	i int64
+}
+
+func main() {
+	i := 1
+	p := &i
+	s := s{i: 1}
+	_ = s
+	runtime.Breakpoint()
+	println(i, p)
+}

pkg/proc/proc_test.go

@@ -4117,3 +4117,21 @@ func TestIssue1374(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue1432(t *testing.T) {
+	// Check that taking the address of a struct, casting it into a pointer to
+	// the struct's type and then accessing a member field will still:
+	// - perform auto-dereferencing on struct member access
+	// - yield a Variable that's ultimately assignable (i.e. has an address)
+	withTestProcess("issue1432", t, func(p proc.Process, fixture protest.Fixture) {
+		assertNoError(proc.Continue(p), t, "Continue")
+		svar := evalVariable(p, t, "s")
+		t.Logf("%#x", svar.Addr)
+
+		scope, err := proc.GoroutineScope(p.CurrentThread())
+		assertNoError(err, t, "GoroutineScope()")
+
+		err = scope.SetVariable(fmt.Sprintf("(*\"main.s\")(%#x).i", svar.Addr), "10")
+		assertNoError(err, t, "SetVariable")
+	})
+}

pkg/proc/variables.go

@@ -932,6 +932,10 @@ func (v *Variable) maybeDereference() *Variable {
 
 	switch t := v.RealType.(type) {
 	case *godwarf.PtrType:
+		if v.Addr == 0 && len(v.Children) == 1 && v.loaded {
+			// fake pointer variable constructed by casting an integer to a pointer type
+			return &v.Children[0]
+		}
 		ptrval, err := readUintRaw(v.mem, uintptr(v.Addr), t.ByteSize)
 		r := v.newVariable("", uintptr(ptrval), t.Type, DereferenceMemory(v.mem))
 		if err != nil {