ExpectIdent returns an identifier string or an error if this Expr is not an identifier.

ExpectLiteralString returns the string represented by this Expr or an error if the Expr is not a literal string.

ExpectSingletonStringList returns the string in this list or an error if this Expr is not a string list of length 1.

GetFunctionFromCall returns the name of the function called for the given call expression, or the empty string if the function being called is not a normal identifier.

ListArtifactsInDepsBzl parses the DEPS.bzl file and returns a map of repo name -> DownloadableArtifact capturing what's in that repo.

DownloadableArtifact represents a single URL/SHA256 pair.