go.tools/ssa: clarify spec of (*builder).complit().

Added test for []*map composite literals containing nested
literal subelements.  This required implementing
(reflect.Value).Map{Keys,Index} in ssa/interp.

Plus two minor fixes in ssa/interp.

R=gri
CC=golang-dev
https://golang.org/cl/20470043

ssa/builder.go

@@ -386,7 +386,7 @@ func (b *builder) addr(fn *Function, e ast.Expr, escaping bool) lvalue {
 			v = fn.addLocal(t, e.Lbrace)
 		}
 		v.Comment = "complit"
-		b.compLit(fn, v, e, t) // initialize in place
+		b.compLit(fn, v, e) // initialize in place
 		return &address{addr: v, expr: e}
 
 	case *ast.ParenExpr:
@@ -470,14 +470,13 @@ func (b *builder) exprInPlace(fn *Function, loc lvalue, e ast.Expr) {
 		}
 
 		if _, ok := loc.(*address); ok {
-			typ := loc.typ()
-			if _, ok := typ.Underlying().(*types.Interface); ok {
+			if _, ok := loc.typ().Underlying().(*types.Interface); ok {
 				// e.g. var x interface{} = T{...}
 				// Can't in-place initialize an interface value.
 				// Fall back to copying.
 			} else {
 				addr := loc.address(fn)
-				b.compLit(fn, addr, e, typ) // in place
+				b.compLit(fn, addr, e) // in place
 				emitDebugRef(fn, e, addr, true)
 				return
 			}
@@ -1184,10 +1183,13 @@ func (b *builder) arrayLen(fn *Function, elts []ast.Expr) int64 {
 // Nested composite literals are recursively initialized in place
 // where possible.
 //
-func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit, typ types.Type) {
-	// TODO(adonovan): document how and why typ ever differs from
-	// fn.Pkg.typeOf(e).
-
+// A CompositeLit may have pointer type only in the recursive (nested)
+// case when the type name is implicit.  e.g. in []*T{{}}, the inner
+// literal has type *T behaves like &T{}.
+// In that case, addr must hold a T, not a *T.
+//
+func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit) {
+	typ := deref(fn.Pkg.typeOf(e))
 	switch t := typ.Underlying().(type) {
 	case *types.Struct:
 		for i, e := range e.Elts {
@@ -1250,7 +1252,7 @@ func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit, typ typ
 		if t != at { // slice
 			s := &Slice{X: array}
 			s.setPos(e.Lbrace)
-			s.setType(t)
+			s.setType(typ)
 			emitStore(fn, addr, fn.emit(s))
 		}
 
@@ -1270,12 +1272,6 @@ func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit, typ typ
 			b.exprInPlace(fn, loc, e.Value)
 		}
 
-	case *types.Pointer:
-		// Pointers can only occur in the recursive case; we
-		// strip them off in addr() before calling compLit
-		// again, so that we allocate space for a T not a *T.
-		panic("compLit(fn, addr, e, *types.Pointer")
-
 	default:
 		panic("unexpected CompositeLit type: " + t.String())
 	}

ssa/interp/external.go

@@ -42,6 +42,8 @@ var externals = map[string]externalFn{
 	"(reflect.Value).IsValid":         ext۰reflect۰Value۰IsValid,
 	"(reflect.Value).Kind":            ext۰reflect۰Value۰Kind,
 	"(reflect.Value).Len":             ext۰reflect۰Value۰Len,
+	"(reflect.Value).MapIndex":        ext۰reflect۰Value۰MapIndex,
+	"(reflect.Value).MapKeys":         ext۰reflect۰Value۰MapKeys,
 	"(reflect.Value).NumField":        ext۰reflect۰Value۰NumField,
 	"(reflect.Value).NumMethod":       ext۰reflect۰Value۰NumMethod,
 	"(reflect.Value).Pointer":         ext۰reflect۰Value۰Pointer,

ssa/interp/interp.go

@@ -546,6 +546,9 @@ func runFrame(fr *frame) {
 		}
 		fr.panicking = true
 		fr.panic = recover()
+		if fr.i.mode&EnableTracing != 0 {
+			fmt.Fprintf(os.Stderr, "Panicking: %s.\n", fr.panic)
+		}
 		fr.runDefers()
 		fr.block = fr.fn.Recover // recovered panic
 	}()

ssa/interp/reflect.go

@@ -306,6 +306,50 @@ func ext۰reflect۰Value۰Len(fn *ssa.Function, args []value) value {
 	return nil // unreachable
 }
 
+func ext۰reflect۰Value۰MapIndex(fn *ssa.Function, args []value) value {
+	// Signature: func (reflect.Value) Value
+	tValue := rV2T(args[0]).t.Underlying().(*types.Map).Key()
+	k := rV2V(args[1])
+	switch m := rV2V(args[0]).(type) {
+	case map[value]value:
+		if v, ok := m[k]; ok {
+			return makeReflectValue(tValue, v)
+		}
+
+	case *hashmap:
+		if v := m.lookup(k.(hashable)); v != nil {
+			return makeReflectValue(tValue, v)
+		}
+
+	default:
+		panic(fmt.Sprintf("(reflect.Value).MapIndex(%T, %T)", m, k))
+	}
+	return makeReflectValue(nil, nil)
+}
+
+func ext۰reflect۰Value۰MapKeys(fn *ssa.Function, args []value) value {
+	// Signature: func (reflect.Value) []Value
+	var keys []value
+	tKey := rV2T(args[0]).t.Underlying().(*types.Map).Key()
+	switch v := rV2V(args[0]).(type) {
+	case map[value]value:
+		for k := range v {
+			keys = append(keys, makeReflectValue(tKey, k))
+		}
+
+	case *hashmap:
+		for _, e := range v.table {
+			for ; e != nil; e = e.next {
+				keys = append(keys, makeReflectValue(tKey, e.key))
+			}
+		}
+
+	default:
+		panic(fmt.Sprintf("(reflect.Value).MapKeys(%T)", v))
+	}
+	return keys
+}
+
 func ext۰reflect۰Value۰NumField(fn *ssa.Function, args []value) value {
 	// Signature: func (reflect.Value) int
 	return len(rV2V(args[0]).(structure))

ssa/interp/testdata/coverage.go

@@ -543,3 +543,18 @@ func init() {
 	}()
 	_ = i == j // interface comparison recurses on types
 }
+
+// Composite literals
+
+func init() {
+	type M map[int]int
+	m1 := []*M{{1: 1}, &M{2: 2}}
+	want := "map[1:1] map[2:2]"
+	if got := fmt.Sprint(*m1[0], *m1[1]); got != want {
+		panic(got)
+	}
+	m2 := []M{{1: 1}, M{2: 2}}
+	if got := fmt.Sprint(m2[0], m2[1]); got != want {
+		panic(got)
+	}
+}

ssa/interp/value.go

@@ -359,7 +359,7 @@ func toWriter(w io.Writer, v value) {
 
 	case map[value]value:
 		io.WriteString(w, "map[")
-		sep := " "
+		sep := ""
 		for k, e := range v {
 			io.WriteString(w, sep)
 			sep = " "