Improve fish#Indent()

- Fix: multiline strings should not be modified.
- Fix: "end" is always decreased by one.
- Fix: "case" and "else" are always decreased by one.
- Fix: continued lines are not treated differently.
- Fix: "if", "while", etc followed by "begin" should increment next line
  by two instead of by one.
- Fix: "case" should be one more than "switch".
- Fix: multiline strings and continued lines are considered in the
  calculations for the next line.

autoload/fish.vim

@@ -1,23 +1,109 @@
+function! s:IsString(lnum, col)
+    " Returns "true" if syntax item at the given position is part of fishString.
+    let l:stack = map(synstack(a:lnum, a:col), 'synIDattr(v:val, "name")')
+    return len(filter(l:stack, 'v:val ==# "fishString"'))
+endfunction
+
+function! s:IsContinuedLine(lnum)
+    " Returns "true" if the given line is a continued line.
+    return getline(a:lnum - 1) =~ '\v\\$'
+endfunction
+
+function! s:FindPrevLnum(lnum)
+    " Starting on the given line, search backwards for a line that is not
+    " empty, not part of a string and not a continued line.
+    if a:lnum < 1 || a:lnum > line('$')
+        " First line or wrong value, follow prevnonblank() behaviour and
+        " return zero.
+        return 0
+    endif
+    let l:lnum = prevnonblank(a:lnum)
+    while l:lnum > 0 && ( s:IsContinuedLine(l:lnum) || s:IsString(l:lnum, 1) )
+        let l:lnum = prevnonblank(l:lnum - 1)
+    endwhile
+    return l:lnum
+endfunction
+
+function! s:IsSwitch(lnum)
+    " Returns "true" if the given line is part of a switch block.
+    let l:lnum = a:lnum
+    let l:line = getline(l:lnum)
+    let l:in_block = 0
+    let l:stop_pat = '\v^\s*%(if|else|while|for|begin)>'
+    let l:block_start_pat = '\v^\s*%(if|while|for|switch|begin)>'
+    while l:lnum > 0
+        let l:lnum = prevnonblank(l:lnum - 1)
+        let l:line = getline(l:lnum)
+        if l:line =~# '\v^\s*end>'
+            let l:in_block += 1
+        elseif l:in_block && l:line =~# l:block_start_pat
+            let l:in_block -= 1
+        elseif !l:in_block && l:line =~# l:stop_pat
+            return 0
+        elseif !l:in_block && l:line =~# '\v^\s*switch>'
+            return 1
+        endif
+    endwhile
+    return 0
+endfunction
+
 function! fish#Indent()
-    let l:shiftwidth = shiftwidth()
-    let l:prevlnum = prevnonblank(v:lnum - 1)
-    if l:prevlnum ==# 0
+    let l:line = getline(v:lnum)
+    if s:IsString(v:lnum, 1)
+        return indent(v:lnum)
+    endif
+    " shiftwidth can be misleading in recent versions, use shiftwidth() if
+    " it is available.
+    if exists('*shiftwidth')
+        let l:shiftwidth = shiftwidth()
+    else
+        let l:shiftwidth = &shiftwidth
+    endif
+    let l:prevlnum = s:FindPrevLnum(v:lnum - 1)
+    if l:prevlnum == 0
         return 0
     endif
-    let l:indent = 0
+    let l:shift = 0
     let l:prevline = getline(l:prevlnum)
-    if l:prevline =~# '\v^\s*switch>'
-        let l:indent = l:shiftwidth * 2
-    elseif l:prevline =~# '\v^\s*%(begin|if|else|while|for|function|case)>'
-        let l:indent = l:shiftwidth
+    let l:previndent = indent(l:prevlnum)
+    if s:IsContinuedLine(v:lnum)
+        " It is customary to increment indentation of continued lines by three
+        " or a custom value defined by the user if available.
+        let l:previndent = indent(v:lnum - 1)
+        if s:IsContinuedLine(v:lnum - 1)
+            return l:previndent
+        elseif exists('g:fish_indent_cont')
+            return l:previndent + g:fish_indent_cont
+        elseif exists('g:indent_cont')
+            return l:previndent + g:indent_cont
+        else
+            return l:previndent + 3
+        endif
     endif
-    let l:line = getline(v:lnum)
-    if l:line =~# '\v^\s*end>'
-        return indent(v:lnum) - (l:indent ==# 0 ? l:shiftwidth : l:indent)
-    elseif l:line =~# '\v^\s*%(case|else)>'
-        return indent(v:lnum) - l:shiftwidth
+    if l:prevline =~# '\v^\s*%(begin|if|else|while|for|function|case|switch)>'
+        " First line inside a block, increase by one.
+        let l:shift += 1
+    endif
+    if l:line =~# '\v^\s*%(end|case|else)>'
+        " "end", "case" or "else", decrease by one.
+        let l:shift -= 1
+    endif
+    if l:line =~# '\v^\s*<case>' && l:prevline =~# '\v<switch>'
+        " "case" following "switch", increase by one.
+        let l:shift += 1
+    endif
+    if l:line =~# '\v\s*end>' && s:IsSwitch(v:lnum)
+        " "end" ends switch block, decrease by one more so it matches
+        " the indentation of "switch".
+        let l:shift -= 1
+    endif
+    if l:prevline =~# '\v^\s*%(if|while|for|else|switch|end)>.*<begin>'
+        " "begin" after start of block, increase by one.
+        let l:shift += 1
     endif
-    return indent(l:prevlnum) + l:indent
+    let l:indent = l:previndent + l:shift * l:shiftwidth
+    " Only return zero or positive numbers.
+    return l:indent < 0 ? 0 : l:indent
 endfunction
 
 function! fish#Format()

indent/fish.vim

@@ -1,2 +1,3 @@
 setlocal indentexpr=fish#Indent()
+setlocal indentkeys=!^F,o,O
 setlocal indentkeys+==end,=else,=case