// dependencies of a, so that we can be sure that,
				// other than a.buildID, b.linkActionID is only accessing
				// build IDs of completed actions.
				oldBuildID := a.buildID
				a.buildID = id[1] + buildIDSeparator + id[2]
				linkID := buildid.HashToString(b.linkActionID(a.triggers[0]))
				if id[0] == linkID {
					// Best effort attempt to display output from the compile and link steps.

		// them anyway, but just make sure. This is required by the build ID-based
		// shortcut in (*Builder).useCache(a1), which will call b.linkActionID(a).
		// In order for that linkActionID call to compute the right action ID, all the
		// dependencies of a (except a1) must have completed building and have
		// recorded their build IDs.

	if f, err := os.Open(vcfg.VetxOutput); err == nil {
		a.built = vcfg.VetxOutput
		cache.Default().Put(key, f)
		f.Close()
	}

	return runErr
}

// linkActionID computes the action ID for a link action.
func (b *Builder) linkActionID(a *Action) cache.ActionID {
	p := a.Package
	h := cache.NewHash("link " + p.ImportPath)

	// Toolchain-independent configuration.
	fmt.Fprintf(h, "link\n")