go/ssa: add list-of-tests constant to generated testmain package

And log its value in godoc -analysis.

Related to issue 8968

Change-Id: I96a96922a3fa5c434c69e0faff1cc8ec4686b6f2
Reviewed-on: https://go-review.googlesource.com/3154
Reviewed-by: Robert Griesemer <gri@golang.org>

go/ssa/testmain.go

@@ -12,8 +12,10 @@ import (
 	"go/ast"
 	"go/token"
 	"os"
+	"sort"
 	"strings"
 
+	"golang.org/x/tools/go/exact"
 	"golang.org/x/tools/go/types"
 )
 
@@ -118,25 +120,33 @@ func (prog *Program) CreateTestMainPackage(pkgs ...*Package) *Package {
 	}
 
 	// Initialize packages to test.
+	var pkgpaths []string
 	for _, pkg := range pkgs {
 		var v Call
 		v.Call.Value = pkg.init
 		v.setType(types.NewTuple())
 		init.emit(&v)
+
+		pkgpaths = append(pkgpaths, pkg.Object.Path())
 	}
+	sort.Strings(pkgpaths)
 	init.emit(new(Return))
 	init.finishBody()
 	testmain.init = init
 	testmain.Object.MarkComplete()
 	testmain.Members[init.name] = init
 
-	main := &Function{
-		name:      "main",
-		Signature: new(types.Signature),
-		Synthetic: "test main function",
-		Prog:      prog,
-		Pkg:       testmain,
-	}
+	// For debugging convenience, define an unexported const
+	// that enumerates the packages.
+	packagesConst := types.NewConst(token.NoPos, testmain.Object, "packages", tString,
+		exact.MakeString(strings.Join(pkgpaths, " ")))
+	memberFromObject(testmain, packagesConst, nil)
+
+	// Create main *types.Func and *ssa.Function
+	mainFunc := types.NewFunc(token.NoPos, testmain.Object, "main", new(types.Signature))
+	memberFromObject(testmain, mainFunc, nil)
+	main := testmain.Func("main")
+	main.Synthetic = "test main function"
 
 	main.startBody()
 

godoc/analysis/analysis.go

@@ -57,6 +57,7 @@ import (
 	"strings"
 	"sync"
 
+	"golang.org/x/tools/go/exact"
 	"golang.org/x/tools/go/loader"
 	"golang.org/x/tools/go/pointer"
 	"golang.org/x/tools/go/ssa"
@@ -400,6 +401,9 @@ func Run(pta bool, result *Result) {
 	var mainPkgs []*ssa.Package
 	if testmain := prog.CreateTestMainPackage(allPackages...); testmain != nil {
 		mainPkgs = append(mainPkgs, testmain)
+		if p := testmain.Const("packages"); p != nil {
+			log.Printf("Tested packages: %v", exact.StringVal(p.Value.Value))
+		}
 	}
 	for _, pkg := range allPackages {
 		if pkg.Object.Name() == "main" && pkg.Func("main") != nil {