Fix HandleLSPDiagnostics buffer match logic.

To find the buffer corresponding to URIs reported by LSP the
HandleLSPDiagnostics() method uses the built-in bufnr() function. From
the documentation we learn that the first parameter of bufnr() is
an expression, not a path.

EclipseLSP will report project wide errors (e.g. gradle errors) that are
not related to any actual source file with an URI that corresponds to the
project root folder, e.g:

   file:///home/username/Projects/gradle-simple

This URI will match any open buffer of files within the project root
hiearchy, thus project-wide errors appear as part of every file within
the project, e.g:

   file:///home/username/Projects/gradle-simple/src/main/java/Hello.java

To fix this, this MR adds '^' to the beginning and '$' at the end of the
URI path to force an exact match. This is how is recommended in vim
help (see :h bufname).

0 files changed, 0 insertions, 0 deletions