// to the go.mod file, or may have made an erroneous hand-edit that causes
		// it to be untidy.)
		//
		// Promoting an indirect dependency to a root adds the next layer of its
		// dependencies to the module graph, which may increase the selected
		// versions of other modules from which we have already loaded packages.

	//
	// The direct map is keyed by module paths, not module versions. When a
	// module's selected version changes, we assume that it remains direct if the
	// previous version was a direct dependency. That assumption might not hold in
	// rare cases (such as if a dependency splits out a nested module, or merges a
	// nested module back into a parent module).
	direct map[string]bool

	graphOnce sync.Once // guards writes to (but not reads from) graph

updates go.mod to require those versions, and downloads source code into the
module cache.

To add a dependency for a package or upgrade it to its latest version:

	go get example.com/pkg

To upgrade or downgrade a package to a specific version:

	go get example.com/pkg@v1.2.3

To remove a dependency on a module and downgrade modules that require it:

	go get example.com/mod@none

	restore = addVar(sys, 1)
	defer restore()
	tg.wantStale("p1", "stale dependency: runtime/internal", "./testgo list claims p1 is NOT stale, incorrectly, after changing sys.go")
	restore()
	tg.wantNotStale("p1", "", "./testgo list claims p1 is stale, incorrectly, after changing back to old release")
	addVar(sys, 2)
	tg.wantStale("p1", "stale dependency: runtime", "./testgo list claims p1 is NOT stale, incorrectly, after changing sys.go again")

	os.Setenv("GOOS", goos)

	timelog("build", "go_bootstrap")
	xprintf("Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.\n")
	install("runtime")     // dependency not visible in sources; also sets up textflag.h
	install("time/tzdata") // no dependency in sources; creates generated file
	install("cmd/go")
	if vflag > 0 {
		xprintf("\n")
	}

		roots = append(roots, module.Version{Path: "toolchain", Version: toolchain})
		// Leave the toolchain as indirect: nothing in the user's module directly
		// imports a package from the toolchain, and (like an indirect dependency in
		// a module without graph pruning) we may remove the toolchain line
		// automatically if the 'go' version is changed so that it implies the exact
		// same toolchain.
	}
	return roots
}

func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
	return c.loadType(dtype, pos, "")
}

// loadType recursively loads the requested dtype and its dependency graph.
func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Type {
	// Always recompute bad pointer typedefs, as the set of such
	// typedefs changes as we see more types.
	checkCache := true

			// meta-files summary file written by writeCoverMetaAct,
			// so add a dependence edge from writeCoverMetaAct to the
			// run action.
			runAction.Deps = append(runAction.Deps, writeCoverMetaAct)
			if !p.IsTestOnly() {
				// Package p is not test only, meaning that the build
				// action for p may generate a static meta-data file.
				// Add a dependence edge from p to writeCoverMetaAct,

			"c = 0", "d = 0", "b = d + c", "e = 0", "a = e + c",
		}},
		// emit an initializer for n:1 initializations only once (not for each node
		// on the lhs which may appear in different order in the dependency graph)
		{`package p12; var (a = x; b = 0; x, y = m[0]; m map[int]int)`, []string{
			"b = 0", "x, y = m[0]", "a = x",
		}},
		// test case from spec section on package initialization
		{`package p12

(Not x) => (XORconst [1] x)

// Merge logical operations
(AND x (NOR y y)) => (ANDN x y)
(OR x (NOR y y)) => (ORN x y)

// Lowering comparisons
(EqB x y)  => (ANDconst [1] (EQV x y))
// Sign extension dependence on operand sign sets up for sign/zero-extension elision later
(Eq(8|16) x y) && x.Type.IsSigned() && y.Type.IsSigned() => (Equal (CMPW (SignExt(8|16)to32 x) (SignExt(8|16)to32 y)))