go/build: make TestDependencies work again

CL 243940 accidentally broke TestDependencies such that it always passed.
Make it work again, and add a test so that it won't break in the same way.

This revealed that the new embed package was missing from TestDepencies,
so add it.

Fixes #43249

Change-Id: I02b3e38dd35ad88880c4344d46de13b7639aa4c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/279073
Trust: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: ianlancetaylor

src/go/build/deps_test.go

@@ -10,6 +10,7 @@ package build
 import (
 	"bytes"
 	"fmt"
+	"go/token"
 	"internal/testenv"
 	"io/fs"
 	"os"
@@ -162,6 +163,9 @@ var depsRules = `
 	< os
 	< os/signal;
 
+	io/fs
+	< embed;
+
 	unicode, fmt !< os, os/signal;
 
 	os/signal, STR
@@ -602,6 +606,7 @@ func findImports(pkg string) ([]string, error) {
 	}
 	var imports []string
 	var haveImport = map[string]bool{}
+	fset := token.NewFileSet()
 	for _, file := range files {
 		name := file.Name()
 		if name == "slice_go14.go" || name == "slice_go18.go" {
@@ -611,8 +616,10 @@ func findImports(pkg string) ([]string, error) {
 		if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
 			continue
 		}
-		var info fileInfo
-		info.name = filepath.Join(dir, name)
+		info := fileInfo{
+			name: filepath.Join(dir, name),
+			fset: fset,
+		}
 		f, err := os.Open(info.name)
 		if err != nil {
 			return nil, err
@@ -840,3 +847,22 @@ func TestStdlibLowercase(t *testing.T) {
 		}
 	}
 }
+
+// TestFindImports tests that findImports works.  See #43249.
+func TestFindImports(t *testing.T) {
+	imports, err := findImports("go/build")
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Logf("go/build imports %q", imports)
+	want := []string{"bytes", "os", "path/filepath", "strings"}
+wantLoop:
+	for _, w := range want {
+		for _, imp := range imports {
+			if imp == w {
+				continue wantLoop
+			}
+		}
+		t.Errorf("expected to find %q in import list", w)
+	}
+}