proc: Update map reading code for Go 1.12 (#1532)

Go 1.12 introduced a change to the internal map representation where
empty map cells can be marked with a tophash value of 1 instead of just
0.

Fixes #1531

_fixtures/issue1531.go

+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+type W struct {
+	x int
+	y int
+}
+
+func main() {
+	testMaps()
+}
+
+func testMaps() {
+
+	m := make(map[string]W)
+
+	m["t"] = W{}
+	m["s"] = W{}
+	m["r"] = W{}
+	m["v"] = W{}
+
+	mm := map[string]W{
+		"r": {},
+		"s": {},
+		"t": {},
+		"v": {},
+	}
+
+	delete(mm, "s")
+	delete(m, "t")
+	runtime.Breakpoint()
+	fmt.Println(m, mm)
+}

pkg/proc/variables.go

@@ -18,6 +18,7 @@ import (
 	"github.com/go-delve/delve/pkg/dwarf/godwarf"
 	"github.com/go-delve/delve/pkg/dwarf/op"
 	"github.com/go-delve/delve/pkg/dwarf/reader"
+	"github.com/go-delve/delve/pkg/goversion"
 )
 
 const (
@@ -28,8 +29,10 @@ const (
 	chanRecv = "chan receive"
 	chanSend = "chan send"
 
-	hashTophashEmpty = 0 // used by map reading code, indicates an empty bucket
-	hashMinTopHash   = 4 // used by map reading code, indicates minimum value of tophash that isn't empty or evacuated
+	hashTophashEmptyZero = 0 // used by map reading code, indicates an empty cell
+	hashTophashEmptyOne  = 1 // used by map reading code, indicates an empty cell in Go 1.12 and later
+	hashMinTopHashGo111  = 4 // used by map reading code, indicates minimum value of tophash that isn't empty or evacuated, in Go1.11
+	hashMinTopHashGo112  = 5 // used by map reading code, indicates minimum value of tophash that isn't empty or evacuated, in Go1.12
 
 	maxFramePrefetchSize = 1 * 1024 * 1024 // Maximum prefetch size for a stack frame
 
@@ -1763,6 +1766,9 @@ type mapIterator struct {
 	maxNumBuckets uint64 // maximum number of buckets to scan
 
 	idx int64
+
+	hashTophashEmptyOne uint64 // Go 1.12 and later has two sentinel tophash values for an empty cell, this is the second one (the first one hashTophashEmptyZero, the same as Go 1.11 and earlier)
+	hashMinTopHash      uint64 // minimum value of tophash for a cell that isn't either evacuated or empty
 }
 
 // Code derived from go/src/runtime/hashmap.go
@@ -1814,6 +1820,13 @@ func (v *Variable) mapIterator() *mapIterator {
 		return nil
 	}
 
+	it.hashTophashEmptyOne = hashTophashEmptyZero
+	it.hashMinTopHash = hashMinTopHashGo111
+	if producer := v.bi.Producer(); producer != "" && goversion.ProducerAfterOrEqual(producer, 1, 12) {
+		it.hashTophashEmptyOne = hashTophashEmptyOne
+		it.hashMinTopHash = hashMinTopHashGo112
+	}
+
 	return it
 }
 
@@ -1851,7 +1864,7 @@ func (it *mapIterator) nextBucket() bool {
 			oldb := it.oldbuckets.clone()
 			oldb.Addr += uintptr(uint64(it.oldbuckets.DwarfType.Size()) * oldbidx)
 
-			if mapEvacuated(oldb) {
+			if it.mapEvacuated(oldb) {
 				break
 			}
 
@@ -1953,7 +1966,7 @@ func (it *mapIterator) next() bool {
 			return false
 		}
 		it.idx++
-		if h != hashTophashEmpty {
+		if h != hashTophashEmptyZero && h != it.hashTophashEmptyOne {
 			return true
 		}
 	}
@@ -1969,7 +1982,7 @@ func (it *mapIterator) value() *Variable {
 	return v
 }
 
-func mapEvacuated(b *Variable) bool {
+func (it *mapIterator) mapEvacuated(b *Variable) bool {
 	if b.Addr == 0 {
 		return true
 	}
@@ -1983,7 +1996,8 @@ func mapEvacuated(b *Variable) bool {
 		if err != nil {
 			return true
 		}
-		return tophash0 > hashTophashEmpty && tophash0 < hashMinTopHash
+		//TODO: this needs to be > hashTophashEmptyOne for go >= 1.12
+		return tophash0 > it.hashTophashEmptyOne && tophash0 < it.hashMinTopHash
 	}
 	return true
 }

service/test/variables_test.go

@@ -3,6 +3,7 @@ package service_test
 import (
 	"errors"
 	"fmt"
+	"go/constant"
 	"runtime"
 	"sort"
 	"strings"
@@ -1197,3 +1198,45 @@ func TestCallFunction(t *testing.T) {
 		}
 	})
 }
+
+func TestIssue1531(t *testing.T) {
+	// Go 1.12 introduced a change to the map representation where empty cells can be marked with 1 instead of just 0.
+	withTestProcess("issue1531", t, func(p proc.Process, fixture protest.Fixture) {
+		assertNoError(proc.Continue(p), t, "Continue()")
+
+		hasKeys := func(mv *proc.Variable, keys ...string) {
+			n := 0
+			for i := 0; i < len(mv.Children); i += 2 {
+				cv := &mv.Children[i]
+				s := constant.StringVal(cv.Value)
+				found := false
+				for j := range keys {
+					if keys[j] == s {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Errorf("key %q not allowed", s)
+					return
+				}
+				n++
+			}
+			if n != len(keys) {
+				t.Fatalf("wrong number of keys found")
+			}
+		}
+
+		mv, err := evalVariable(p, "m", pnormalLoadConfig)
+		assertNoError(err, t, "EvalVariable(m)")
+		cmv := api.ConvertVar(mv)
+		t.Logf("m = %s", cmv.SinglelineString())
+		hasKeys(mv, "s", "r", "v")
+
+		mmv, err := evalVariable(p, "mm", pnormalLoadConfig)
+		assertNoError(err, t, "EvalVariable(mm)")
+		cmmv := api.ConvertVar(mmv)
+		t.Logf("mm = %s", cmmv.SinglelineString())
+		hasKeys(mmv, "r", "t", "v")
+	})
+}