revset: delay showing parse error for the revset alias until it is referred Before this patch, a problematic revset alias aborts execution immediately, even if it isn't referred in the specified revset. If old "hg" may be used too (for example, bisecting Mercurial itself), it is also difficult to write alias definitions using features newly introduced by newer "hg" into configuration files, because such alias definitions cause unexpected abortion at parsing revset aliases with old "hg". This patch delays showing parse error for the revset alias until it is actually referred at runtime. This patch detects referring problematic aliases in "_expandaliases" by examination of "revsetalias.error", which is initialized with the error message only when parsing fails. For usability, this patch also warns about problematic aliases, even if they aren't referred at runtime. This should help users to know potential problems in their alias definitions earlier.