shortest: extract function for checking if a prefix is a revnum Much of isvalid() was about testing if a prefix is a valid revnum. I want to reuse that soon, so let's move it out. There is no significant slowdown from the function call overhead. Differential Revision: https://phab.mercurial-scm.org/D3460

shortest: rename "test" variable to "prefix" Sorry if this is considered churn, but "prefix" just seems much clearer to me. Differential Revision: https://phab.mercurial-scm.org/D3459

shortest: move some safe code out of exception block The RevlogError and WdirUnsupported could be raised by _partialmatch(), but not by the rest of isvalid(), so let's move the rest out to make it clearer. Differential Revision: https://phab.mercurial-scm.org/D3458

revlog: don't say "not found" on internal error If index_node() returned NULL, then index_find_node() and and nt_partialmatch() used to return -2 to signal that the node was not found. However, we were passing in a revnum to index_node() that we knew should exist, so the only reason it could return NULL was due to some internal error or perhaps out of memory. Let's not use "not found" for these cases. I suppose we never noticed this because these error never happen in practice. I think there are more places where we should error out instead of reporting that the node was not found, but the cases mentioned above were all I cared about right now (because using the same error code for all failures simplified some future patches). Differential Revision: https://phab.mercurial-scm.org/D3457