go/analysis,go/ssa: initialize the types.Info.Instances map

Update a couple places where we should initialize the
types.Info.Instances map:
 - The unitchecker may be used with analyzers that expect the Instances
   map to be populated.
 - go/ssa will eventually support instances.

Change-Id: Id3dafe57430e5710ee91215a9586b09a87470b15
Reviewed-on: https://go-review.googlesource.com/c/tools/+/357757
Trust: Robert Findley <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Tim King <[email protected]>

Author: findleyr

go/analysis/unitchecker/unitchecker.go

@@ -51,6 +51,7 @@ import (
 	"golang.org/x/tools/go/analysis"
 	"golang.org/x/tools/go/analysis/internal/analysisflags"
 	"golang.org/x/tools/go/analysis/internal/facts"
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // A Config describes a compilation unit to be analyzed.
@@ -233,6 +234,8 @@ func run(fset *token.FileSet, cfg *Config, analyzers []*analysis.Analyzer) ([]re
 		Scopes:     make(map[ast.Node]*types.Scope),
 		Selections: make(map[*ast.SelectorExpr]*types.Selection),
 	}
+	typeparams.InitInstanceInfo(info)
+
 	pkg, err := tc.Check(cfg.ImportPath, fset, files, info)
 	if err != nil {
 		if cfg.SucceedOnTypecheckFailure {

go/ssa/testmain.go

@@ -21,6 +21,8 @@ import (
 	"os"
 	"strings"
 	"text/template"
+
+	"golang.org/x/tools/internal/typeparams"
 )
 
 // FindTests returns the Test, Benchmark, and Example functions
@@ -180,6 +182,7 @@ func (prog *Program) CreateTestMainPackage(pkg *Package) *Package {
 		Scopes:     make(map[ast.Node]*types.Scope),
 		Selections: make(map[*ast.SelectorExpr]*types.Selection),
 	}
+	typeparams.InitInstanceInfo(info)
 	testmainPkg, err := conf.Check(path, prog.Fset, files, info)
 	if err != nil {
 		log.Fatalf("internal error type-checking %s: %v", path, err)