go/callgraph/vta: allow pointer to type parameter in sliceArrayElem

Fixes a bug in sliceArrayElem that panicked when when a pointer to type
parameter type where the type parameters is indexable, but does not have
a core type.

Example:

	func set[T [1]I | [2]I](arr *T, i int, x I) {
		(*arr)[i] = x
	}

Fixes golang/go#59754

Change-Id: I196e2b882ffa84a13b7c6153796b38c1b8707722
Reviewed-on: https://go-review.googlesource.com/c/tools/+/492739
Commit-Queue: Tim King <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Zvonimir Pavlinovic <[email protected]>
Run-TryBot: Tim King <[email protected]>

Author: timothy-king

go/callgraph/vta/helpers_test.go

@@ -5,12 +5,14 @@
 package vta
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
 	"go/parser"
 	"io/ioutil"
 	"sort"
 	"strings"
+	"testing"
 
 	"golang.org/x/tools/go/callgraph"
 	"golang.org/x/tools/go/ssa/ssautil"
@@ -114,3 +116,12 @@ func callGraphStr(g *callgraph.Graph) []string {
 	}
 	return gs
 }
+
+// Logs the functions of prog to t.
+func logFns(t testing.TB, prog *ssa.Program) {
+	for fn := range ssautil.AllFunctions(prog) {
+		var buf bytes.Buffer
+		fn.WriteTo(&buf)
+		t.Log(buf.String())
+	}
+}

go/callgraph/vta/testdata/src/arrays_generics.go

@@ -0,0 +1,28 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// go:build ignore
+
+package testdata
+
+type F func()
+
+func set[T [1]F | [2]F](arr *T, i int) {
+	// Indexes into a pointer to an indexable type T and T does not have a coretype.
+	// SSA instruction:	t0 = &arr[i]
+	(*arr)[i] = bar
+}
+
+func bar() {
+	print("here")
+}
+
+func Foo() {
+	var arr [1]F
+	set(&arr, 0)
+	arr[0]()
+}
+
+// WANT:
+// Foo: set[[1]testdata.F](t0, 0:int) -> set[[1]testdata.F]; t3() -> bar

go/callgraph/vta/utils.go

@@ -123,7 +123,14 @@ func functionUnderPtr(t types.Type) types.Type {
 func sliceArrayElem(t types.Type) types.Type {
 	switch u := t.Underlying().(type) {
 	case *types.Pointer:
-		return u.Elem().Underlying().(*types.Array).Elem()
+		switch e := u.Elem().Underlying().(type) {
+		case *types.Array:
+			return e.Elem()
+		case *types.Interface:
+			return sliceArrayElem(e) // e is a type param with matching element types.
+		default:
+			panic(t)
+		}
 	case *types.Array:
 		return u.Elem()
 	case *types.Slice:

go/callgraph/vta/vta_test.go

@@ -124,18 +124,26 @@ func TestVTACallGraphGenerics(t *testing.T) {
 	}
 
 	// TODO(zpavlinovic): add more tests
-	file := "testdata/src/callgraph_generics.go"
-	prog, want, err := testProg(file, ssa.InstantiateGenerics)
-	if err != nil {
-		t.Fatalf("couldn't load test file '%s': %s", file, err)
-	}
-	if len(want) == 0 {
-		t.Fatalf("couldn't find want in `%s`", file)
+	files := []string{
+		"testdata/src/arrays_generics.go",
+		"testdata/src/callgraph_generics.go",
 	}
+	for _, file := range files {
+		t.Run(file, func(t *testing.T) {
+			prog, want, err := testProg(file, ssa.InstantiateGenerics)
+			if err != nil {
+				t.Fatalf("couldn't load test file '%s': %s", file, err)
+			}
+			if len(want) == 0 {
+				t.Fatalf("couldn't find want in `%s`", file)
+			}
 
-	g := CallGraph(ssautil.AllFunctions(prog), cha.CallGraph(prog))
-	got := callGraphStr(g)
-	if diff := setdiff(want, got); len(diff) != 0 {
-		t.Errorf("computed callgraph %v should contain %v (diff: %v)", got, want, diff)
+			g := CallGraph(ssautil.AllFunctions(prog), cha.CallGraph(prog))
+			got := callGraphStr(g)
+			if diff := setdiff(want, got); len(diff) != 0 {
+				t.Errorf("computed callgraph %v should contain %v (diff: %v)", got, want, diff)
+				logFns(t, prog)
+			}
+		})
 	}
 }