go.tools/oracle: pointsto: if the queried expression is an lvalue, use the type of its value, not its address.

(Probable regression caused by recent changes to VarValue.)

+ regression test.

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/116160044

oracle/pointsto.go

@@ -132,8 +132,10 @@ func ssaValueForExpr(prog *ssa.Program, qinfo *loader.PackageInfo, path []ast.No
 func runPTA(o *Oracle, v ssa.Value, isAddr bool) (ptrs []pointerResult, err error) {
 	buildSSA(o)
 
+	T := v.Type()
 	if isAddr {
 		o.ptaConfig.AddIndirectQuery(v)
+		T = deref(T)
 	} else {
 		o.ptaConfig.AddQuery(v)
 	}
@@ -150,7 +152,7 @@ func runPTA(o *Oracle, v ssa.Value, isAddr bool) (ptrs []pointerResult, err erro
 	}
 	pts := ptr.PointsTo()
 
-	if pointer.CanHaveDynamicTypes(v.Type()) {
+	if pointer.CanHaveDynamicTypes(T) {
 		// Show concrete types for interface/reflect.Value expression.
 		if concs := pts.DynamicTypes(); concs.Len() > 0 {
 			concs.Iterate(func(conc types.Type, pta interface{}) {
@@ -163,7 +165,7 @@ func runPTA(o *Oracle, v ssa.Value, isAddr bool) (ptrs []pointerResult, err erro
 		// Show labels for other expressions.
 		labels := pts.Labels()
 		sort.Sort(byPosAndString(labels)) // to ensure determinism
-		ptrs = append(ptrs, pointerResult{v.Type(), labels})
+		ptrs = append(ptrs, pointerResult{T, labels})
 	}
 	sort.Sort(byTypeString(ptrs)) // to ensure determinism
 	return ptrs, nil

oracle/testdata/src/main/pointsto.go

@@ -46,7 +46,14 @@ func main() {
 	_ = mapval          // @pointsto mapval "mapval"
 	_ = m               // @pointsto m "m"
 
-	panic(3) // @pointsto builtin-panic "panic"
+	if false {
+		panic(3) // @pointsto builtin-panic "panic"
+	}
+
+	// NB: s.f is addressable per (*ssa.Program).VarValue,
+	// but our query concerns the object, not its address.
+	s := struct{ f interface{} }{f: make(chan bool)}
+	print(s.f) // @pointsto var-ref-s-f "s.f"
 }
 
 func livecode() {} // @pointsto func-live "livecode"

oracle/testdata/src/main/pointsto.golden

@@ -80,6 +80,11 @@ this map[string]*int may point to these objects:
 -------- @pointsto builtin-panic --------
 
 Error: pointer analysis wants an expression of reference type; got ()
+-------- @pointsto var-ref-s-f --------
+this interface{} may contain these dynamic types:
+	chan bool, may point to:
+		makechan
+
 -------- @pointsto func-live --------
 
 Error: pointer analysis did not find expression (dead code?)