go/types: better debugging output for init order computation

Also: Added some test cases for issue #10709.
No impact when debugging output is disabled (default).

For #10709.

Change-Id: I0751befb222c86d46225377a674f6bad2990349e
Reviewed-on: https://go-review.googlesource.com/23442
Reviewed-by: Alan Donovan <adonovan@google.com>

3 files changed, 75 insertions, 13 deletions

diff --git a/src/go/types/api_test.go b/src/go/types/api_test.go
index 8b8ae1bb5d..035ffd6f39 100644
--- a/src/go/types/api_test.go
+++ b/src/go/types/api_test.go
@@ -572,6 +572,47 @@ func TestInitOrderInfo(t *testing.T) {
 		`, []string{
 			"a = next()", "b = next()", "c = next()", "d = next()", "e = next()", "f = next()", "_ = makeOrder()",
 		}},
+		// test case for issue 10709
+		// TODO(gri) enable once the issue is fixed
+		// {`package p13
+
+		// var (
+		//     v = t.m()
+		//     t = makeT(0)
+		// )
+
+		// type T struct{}
+
+		// func (T) m() int { return 0 }
+
+		// func makeT(n int) T {
+		//     if n > 0 {
+		//         return makeT(n-1)
+		//     }
+		//     return T{}
+		// }`, []string{
+		// 	"t = makeT(0)", "v = t.m()",
+		// }},
+		// test case for issue 10709: same as test before, but variable decls swapped
+		{`package p14
+
+		var (
+		    t = makeT(0)
+		    v = t.m()
+		)
+
+		type T struct{}
+
+		func (T) m() int { return 0 }
+
+		func makeT(n int) T {
+		    if n > 0 {
+		        return makeT(n-1)
+		    }
+		    return T{}
+		}`, []string{
+			"t = makeT(0)", "v = t.m()",
+		}},
 	}
 
 	for _, test := range tests {
diff --git a/src/go/types/initorder.go b/src/go/types/initorder.go
index ac9016b46e..cf9b8709d8 100644
--- a/src/go/types/initorder.go
+++ b/src/go/types/initorder.go
@@ -15,25 +15,40 @@ func (check *Checker) initOrder() {
 	// built from several calls to (*Checker).Files. Clear it.
 	check.Info.InitOrder = check.Info.InitOrder[:0]
 
-	// compute the object dependency graph and
-	// initialize a priority queue with the list
-	// of graph nodes
+	// Compute the transposed object dependency graph and initialize
+	// a priority queue with the list of graph nodes.
 	pq := nodeQueue(dependencyGraph(check.objMap))
 	heap.Init(&pq)
 
 	const debug = false
 	if debug {
-		fmt.Printf("package %s: object dependency graph\n", check.pkg.Name())
+		fmt.Printf("Computing initialization order for %s\n\n", check.pkg)
+		fmt.Println("Object dependency graph:")
+		for obj, d := range check.objMap {
+			if len(d.deps) > 0 {
+				fmt.Printf("\t%s depends on\n", obj.Name())
+				for dep := range d.deps {
+					fmt.Printf("\t\t%s\n", dep.Name())
+				}
+			} else {
+				fmt.Printf("\t%s has no dependencies\n", obj.Name())
+			}
+		}
+		fmt.Println()
+
+		fmt.Println("Transposed object dependency graph:")
 		for _, n := range pq {
-			for _, o := range n.out {
-				fmt.Printf("\t%s -> %s\n", n.obj.Name(), o.obj.Name())
+			fmt.Printf("\t%s depends on %d nodes\n", n.obj.Name(), n.in)
+			for _, out := range n.out {
+				fmt.Printf("\t\t%s is dependent\n", out.obj.Name())
 			}
 		}
 		fmt.Println()
-		fmt.Printf("package %s: initialization order\n", check.pkg.Name())
+
+		fmt.Println("Processing nodes:")
 	}
 
-	// determine initialization order by removing the highest priority node
+	// Determine initialization order by removing the highest priority node
 	// (the one with the fewest dependencies) and its edges from the graph,
 	// repeatedly, until there are no nodes left.
 	// In a valid Go program, those nodes always have zero dependencies (after
@@ -45,6 +60,11 @@ func (check *Checker) initOrder() {
 		// get the next node
 		n := heap.Pop(&pq).(*objNode)
 
+		if debug {
+			fmt.Printf("\t%s (src pos %d) depends on %d nodes now\n",
+				n.obj.Name(), n.obj.order(), n.in)
+		}
+
 		// if n still depends on other nodes, we have a cycle
 		if n.in > 0 {
 			mark++ // mark nodes using a different value each time
@@ -86,14 +106,15 @@ func (check *Checker) initOrder() {
 		}
 		init := &Initializer{infoLhs, info.init}
 		check.Info.InitOrder = append(check.Info.InitOrder, init)
-
-		if debug {
-			fmt.Printf("\t%s\n", init)
-		}
 	}
 
 	if debug {
 		fmt.Println()
+		fmt.Println("Initialization order:")
+		for _, init := range check.Info.InitOrder {
+			fmt.Printf("\t%s\n", init)
+		}
+		fmt.Println()
 	}
 }
 
diff --git a/src/go/types/resolver.go b/src/go/types/resolver.go
index 992188f0ff..cb8e72e4a6 100644
--- a/src/go/types/resolver.go
+++ b/src/go/types/resolver.go
@@ -32,7 +32,7 @@ func (d *declInfo) hasInitializer() bool {
 	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
 }
 
-// addDep adds obj as a dependency to d.
+// addDep adds obj to the set of objects d's init expression depends on.
 func (d *declInfo) addDep(obj Object) {
 	m := d.deps
 	if m == nil {