debug: support path substitutions

Add g:go_debug_subtitutions and hook up their use to the debugger so
that binaries that are compiled at a different location than where the
local source exists can be debugged.

Closes #3245

Author: bhcleek

autoload/go/config.vim

@@ -211,6 +211,10 @@ function! go#config#DebugWindows() abort
 
 endfunction
 
+function! go#config#DebugSubstitutePaths() abort
+  return get(g:, 'go_debug_substitute_paths', [])
+endfunction
+
 function! go#config#DebugPreserveLayout() abort
   return get(g:, 'go_debug_preserve_layout', 0)
 endfunction

autoload/go/debug.vim

@@ -158,7 +158,7 @@ function! s:update_breakpoint(res) abort
   endif
 
   exe bufs[0][0] 'wincmd w'
-  let filename = state.currentThread.file
+  let filename = s:substituteRemotePath(state.currentThread.file)
   let linenr = state.currentThread.line
   let oldfile = fnamemodify(expand('%'), ':p:gs!\\!/!')
   if oldfile != filename
@@ -357,7 +357,7 @@ function! s:goto_file() abort
     return
   endif
   exe bufs[0][0] 'wincmd w'
-  let filename = m[1]
+  let filename = s:substituteRemotePath(m[1])
   let linenr = m[2]
   let oldfile = fnamemodify(expand('%'), ':p:gs!\\!/!')
   if oldfile != filename
@@ -1418,7 +1418,7 @@ endfunction
 
 " Toggle breakpoint. Returns 0 on success and 1 on failure.
 function! go#debug#Breakpoint(...) abort
-  let l:filename = fnamemodify(expand('%'), ':p:gs!\\!/!')
+  let l:filename = s:substituteLocalPath(fnamemodify(expand('%'), ':p:gs!\\!/!'))
   let l:linenr = line('.')
 
   " Get line number from argument.
@@ -1737,6 +1737,24 @@ function! s:restore_mapping(maparg)
   return
 endfunction
 
+function! s:substituteRemotePath(path) abort
+  return s:substitutePath(a:path, go#config#DebugSubstitutePaths())
+endfunction
+
+function! s:substituteLocalPath(path) abort
+  return s:substitutePath(a:path, map(deepcopy(go#config#DebugSubstitutePaths()), '[v:val[1], v:val[0]]'))
+endfunction
+
+function! s:substitutePath(path, substitutions) abort
+  for [l:from, l:to] in a:substitutions
+    if l:from[0:len(a:path)-1] != l:from
+      continue
+    endif
+    return printf('%s%s', l:to, a:path[len(l:from)])
+  endfor
+  return a:path
+endfunction
+
 " restore Vi compatibility settings
 let &cpo = s:cpo_save
 unlet s:cpo_save

doc/vim-go.txt

@@ -2517,6 +2517,17 @@ Preserve window layout in debugging mode. This setting is considered only when
 |'g:go_debug_windows'| is not empty.
 >
   let g:go_debug_preserve_layout = 0
+<
+                                               *'g:go_debug_substitute_paths'*
+
+Substitute paths in the debugger. This is a list of lists, where each element
+is a list where the remote path (the from side) is the first element and the
+local path (the to side) is the second element. These are necessary when the
+binary being debugged was not built from the same location that its source
+resides locally. By default it is empty.
+
+>
+  let g:go_debug_substitute_paths = [['/compiled/from', '/cloned/to']]
 <
                                                        *'g:go_debug_mappings'*