Rather than stat-ing each argument and taking different code paths
depending on whether it's a directory or not, we can leverage
the fact that filepath.WalkDir works on regular files and already
has to figure out whether each file it walks is a directory or not.
We can then implement "always format non-directory arguments"
by looking at whether the path we are walking is the original argument,
meaning we are walking the top file.
For full clarity, we expand the skipping logic with a switch,
as before it was a bit confusing how we could `return err`
on directories and other non-Go files.
Given that we discard directories separately now,
simplify isGoFile to just be about filenames.
While here, also note that we called AddReport inside WalkDir;
this is unnecessary, as we can return the error for the same effect.
Change-Id: I50ab94710143f19bd8dd95a69e01a3dd228e397e
Reviewed-on: https://go-review.googlesource.com/c/go/+/700115 Reviewed-by: Sean Liao <sean@liao.dev> Reviewed-by: Michael Pratt <mpratt@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>