vulncheck: add support for generics

Make ssa instantiate generics.

Fixes golang/go#57174

Change-Id: I2d2e28a48e3a64df3d4d415b4629fe3e0a1ba28d
Reviewed-on: https://go-review.googlesource.com/c/vuln/+/456436
Reviewed-by: Fnu Harshavardhana <[email protected]>
Run-TryBot: Zvonimir Pavlinovic <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>

vulncheck/source_test.go

@@ -848,3 +848,55 @@ func TestRecursion(t *testing.T) {
 		t.Errorf("want 3 functions (X, y, Vuln) in vulnerability graph; got %v", l)
 	}
 }
+
+func TestIssue57174(t *testing.T) {
+	e := packagestest.Export(t, packagestest.Modules, []packagestest.Module{
+		{
+			Name: "golang.org/entry",
+			Files: map[string]interface{}{
+				"x/x.go": `
+			package x
+
+			import "golang.org/bmod/bvuln"
+
+			func P(d [][3]int) {
+				p(d)
+			}
+
+			func p[E interface{ [3]int | [4]int }](d []E) {
+				c := d[0]
+				if c[0] > 0 {
+					bvuln.Vuln()
+				}
+			}
+			`,
+			},
+		},
+		{
+			Name: "golang.org/[email protected]",
+			Files: map[string]interface{}{"bvuln/bvuln.go": `
+			package bvuln
+
+			func Vuln() {}
+			`},
+		},
+	})
+	defer e.Cleanup()
+
+	// Load x as entry package.
+	pkgs, err := test.LoadPackages(e, path.Join(e.Temp(), "entry/x"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(pkgs) != 1 {
+		t.Fatal("failed to load x test package")
+	}
+
+	cfg := &Config{
+		Client: testClient,
+	}
+	_, err = Source(context.Background(), Convert(pkgs), cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+}

vulncheck/utils.go

@@ -24,7 +24,8 @@ import (
 // the ssa program encapsulating the packages and top level
 // ssa packages corresponding to pkgs.
 func buildSSA(pkgs []*Package, fset *token.FileSet) (*ssa.Program, []*ssa.Package) {
-	prog := ssa.NewProgram(fset, ssa.BuilderMode(0))
+	// TODO(#57221): what about entry functions that are generics?
+	prog := ssa.NewProgram(fset, ssa.InstantiateGenerics)
 
 	imports := make(map[*Package]*ssa.Package)
 	var createImports func([]*Package)