go list -e -f '{{range .GoFiles}}{{.}},{{end}}' ./constraint
stdout '^good.go,$'
go list -e -f '{{range .IgnoredGoFiles}}{{.}},{{end}}' ./constraint
stdout '^constraint.go,$'

[cgo] go list -e -f '{{range .XTestGoFiles}}{{.}},{{end}}' ./cgotest
[cgo] stdout '^cgo_test.go,$'

[cgo] go list -e -f '{{range .GoFiles}}{{.}},{{end}}' ./cgoflag
[cgo] stdout '^cgoflag.go,$'

-- go.mod --
module m

go 1.14

        DefaultGODEBUG string  // default GODEBUG setting, for main packages

        // Source files
        GoFiles           []string   // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
        CgoFiles          []string   // .go source files that import "C"
        CompiledGoFiles   []string   // .go files presented to compiler (when using -compiled)

	} else {
		ptest = p
	}

	// External test package.
	if len(p.XTestGoFiles) > 0 {
		pxtest = &Package{
			PackagePublic: PackagePublic{
				Name:       p.Name + "_test",
				ImportPath: p.ImportPath + "_test",
				Root:       p.Root,
				Dir:        p.Dir,
				Goroot:     p.Goroot,
				GoFiles:    p.XTestGoFiles,
				Imports:    p.XTestImports,
				ForTest:    p.ImportPath,
				Module:     p.Module,

	ctxt := build.Default
	pkginfo, err := ctxt.ImportDir(dir, 0)
	if _, nogo := err.(*build.NoGoError); err != nil && !nogo {
		return nil, err
	}

	if *xtestFiles {
		return parseFiles(dir, pkginfo.XTestGoFiles)
	}

	filenames := append(pkginfo.GoFiles, pkginfo.CgoFiles...)
	if *testFiles {
		filenames = append(filenames, pkginfo.TestGoFiles...)
	}
	return parseFiles(dir, filenames)
}

	Imports      []string `yaml:",omitempty"` // import paths used by this package
	TestImports  []string `yaml:",omitempty"` // imports from TestGoFiles
	XTestImports []string `yaml:",omitempty"` // imports from XTestGoFiles
}

// ImportRestriction describes a set of allowable import
// trees for a tree of source code
type ImportRestriction struct {
	// BaseDir is the root of a package tree that is restricted by this

	BinaryOnly    bool     // cannot be rebuilt from source (has //go:binary-only-package comment)

	// Source files
	GoFiles           []string // .go source files (excluding CgoFiles, TestGoFiles, XTestGoFiles)
	CgoFiles          []string // .go source files that import "C"
	IgnoredGoFiles    []string // .go source files ignored for this build (including ignored _test.go files)

	TestEmbedFiles     []string `json:",omitempty"` // files matched by TestEmbedPatterns
	XTestGoFiles       []string `json:",omitempty"` // _test.go files outside package
	XTestImports       []string `json:",omitempty"` // imports from XTestGoFiles
	XTestEmbedPatterns []string `json:",omitempty"` // //go:embed patterns

		// The others are.
		keep := func(list []string) {
			for _, f := range list {
				packageFile[f] = true
			}
		}
		keep(p.GoFiles)
		keep(p.CgoFiles)
		keep(p.TestGoFiles)
		keep(p.XTestGoFiles)
	}

	_, elem := filepath.Split(p.Dir)
	var allRemove []string

	// Remove dir-named executable only if this is package main.
	if p.Name == "main" {
		allRemove = append(allRemove,
			elem,

				embedMap = embedPos
				directives = &p.Directives
			} else {
				// Ignore Imports and Embeds from cgo files if cgo is disabled.
				fileList = &p.IgnoredGoFiles
			}
		case isXTest:
			fileList = &p.XTestGoFiles
			importMap = xTestImportPos
			embedMap = xTestEmbedPos
			directives = &p.XTestDirectives
		case isTest:
			fileList = &p.TestGoFiles
			importMap = testImportPos
			embedMap = testEmbedPos

			// later package. Note that if -coverpkg is in effect
			// p.Internal.Cover.GenMeta will wind up being set for
			// all matching packages.
			if len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 &&
				cfg.BuildCoverPkg == nil &&
				cfg.Experiment.CoverageRedesign {
				p.Internal.Cover.GenMeta = true
			}
		}
	}

	// Prepare build + run + print actions for all packages being tested.