// i.e., locally vendored packages may not be found.
	// The types package does not call Import if an ImporterFrom
	// is present.
	Importer

	// ImportFrom returns the imported package for the given import
	// path when imported by a package file located in dir.
	// If the import failed, besides returning an error, ImportFrom
	// is encouraged to cache and return a package anyway, if one

	// i.e., locally vendored packages may not be found.
	// The types package does not call Import if an ImporterFrom
	// is present.
	Importer

	// ImportFrom returns the imported package for the given import
	// path when imported by a package file located in dir.
	// If the import failed, besides returning an error, ImportFrom
	// is encouraged to cache and return a package anyway, if one

		// imports. TestStdlib will collect errors once for each package.
		return pkg, nil
	}
	return nil, err
}

// getDirPackage gets the package defined in dir from the future cache.
//
// If this is the first goroutine requesting the package, getDirPackage
// type-checks.
func (c *stdlibChecker) getDirPackage(dir string) (*Package, error) {
	c.mu.Lock()
	fut, ok := c.pkgs[dir]
	if !ok {

	return pmain, ptest, pxtest, err
}

// TestPackagesAndErrors returns three packages:
//   - pmain, the package main corresponding to the test binary (running tests in ptest and pxtest).
//   - ptest, the package p compiled with added "package p" test files.
//   - pxtest, the result of compiling any "package p_test" (external) test files.
//
// If the package has no "package p_test" test files, pxtest will be nil.

// and a1.Deps is the actions for building packages directly imported by
// package main (what the compiler needs). The linker needs all packages
// transitively imported by the whole program; addTransitiveLinkDeps
// makes sure those are present in a.Deps.
// If shlib is non-empty, then a corresponds to the build and installation of shlib,

)
-- a/a.go --
package a

import _ "example.com/b"
-- a/a_test.go --
package a_test

import _ "example.com/c"
-- b/go.mod --
module example.com/b

go 1.15
-- b/b.go --
package b
-- b/b_test.go --
package b_test
-- c/go.mod --
module example.com/c

go 1.15

require example.com/d v0.1.0
-- c/c.go --
package c
-- c/c_test.go --
package c_test

	// package, and (if no other modules match) one candidate set for the pattern
	// overall if no existing match is identified in the build list.
	//
	// A query for pattern "all" results in one set for each package transitively
	// imported by the main module.
	//
	// The special query for the "-u" flag results in one set for each
	// otherwise-unconstrained package that has available upgrades.

		// imports. TestStdlib will collect errors once for each package.
		return pkg, nil
	}
	return nil, err
}

// getDirPackage gets the package defined in dir from the future cache.
//
// If this is the first goroutine requesting the package, getDirPackage
// type-checks.
func (c *stdlibChecker) getDirPackage(dir string) (*Package, error) {
	c.mu.Lock()
	fut, ok := c.pkgs[dir]
	if !ok {

// Existing packages should not have their constraints relaxed
// without prior discussion.
// Negative assertions should almost never be removed.
//
// "a < b" means package b can import package a.
//
// See `go doc internal/dag' for the full syntax.
//
// All-caps names are pseudo-names for specific points
// in the dependency lattice.
var depsRules = `
	# No dependencies allowed for any of these packages.
	NONE
	< unsafe

     * If you do not supply any -group option, all packages are placed in one group with the heading "Packages".
     * If the all groups do not include all documented packages,
     * any leftover packages appear in a separate group with the heading "Other Packages".
     * <p>
     * For example, the following option separates the four documented packages into core,