gopls/internal/protocol: optimized DocumentURI.Path for MODCACHE

This CL removes an overly conservative check in DocumentURI.Path
that caused files in the module cache to go through the slow
path of URL parsing, unnecessarily.

Thanks to Josh Bleecher Snyder for pointing it out.

Change-Id: Id64ccb3b0a2b57258f9c4ebca11469fc77e37b3e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/642082
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: adonovan

gopls/internal/protocol/uri.go

@@ -121,9 +121,13 @@ func filename(uri DocumentURI) (string, error) {
 			if b < ' ' || b == 0x7f || // control character
 				b == '%' || b == '+' || // URI escape
 				b == ':' || // Windows drive letter
-				b == '@' || b == '&' || b == '?' { // authority or query
+				b == '&' || b == '?' { // authority or query
 				goto slow
 			}
+			// We do not reject '@' as it cannot be part of the
+			// authority (e.g. user:[email protected]) in a
+			// "file:///" URL, and '@' commonly appears in file
+			// paths such as GOMODCACHE/module@version/...
 		}
 		return rest, nil
 	}