#1428 Start implementing LSP hover support

autoload/ale/hover.vim

@@ -0,0 +1,121 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: Hover support for LSP linters.
+
+let s:hover_map = {}
+
+" Used to get the hover map in tests.
+function! ale#hover#GetMap() abort
+    return deepcopy(s:hover_map)
+endfunction
+
+" Used to set the hover map in tests.
+function! ale#hover#SetMap(map) abort
+    let s:hover_map = a:map
+endfunction
+
+function! ale#hover#ClearLSPData() abort
+    let s:hover_map = {}
+endfunction
+
+function! ale#hover#HandleTSServerResponse(conn_id, response) abort
+endfunction
+
+function! ale#hover#HandleLSPResponse(conn_id, response) abort
+    if has_key(a:response, 'id')
+    \&& has_key(s:hover_map, a:response.id)
+        let l:options = remove(s:hover_map, a:response.id)
+
+        let l:buffer = bufnr('')
+        let [l:line, l:column] = getcurpos()[1:2]
+        let l:end = len(getline(l:line))
+
+        if l:buffer isnot l:options.buffer
+        \|| l:line isnot l:options.line
+        \|| min([l:column, l:end]) isnot min([l:options.column, l:end])
+            " Cancel display the message if the cursor has moved.
+            return
+        endif
+
+        " The result can be a Dictionary item, a List of the same, or null.
+        let l:result = get(a:response, 'result', v:null)
+
+        if l:result is v:null
+            return
+        endif
+
+        let l:result = l:result.contents
+
+        if type(l:result) is type('')
+             " The result can be just a string.
+             let l:result = [l:result]
+        endif
+
+        if type(l:result) is type({})
+            " If the result is an object, then it's markup content.
+            let l:result = [l:result.value]
+        endif
+
+        if type(l:result) is type([])
+            " Replace objects with text values.
+            call map(l:result, 'type(v:val) is type('''') ? v:val : v:val.value')
+            let l:str = join(l:result, "\n")
+            let l:str = substitute(l:str, '^\s*\(.\{-}\)\s*$', '\1', '')
+
+            if !empty(l:str)
+                " Compress multi-line hover messages into one line.
+                let l:str = substitute(l:str, "\n", ' ', 'g')
+                let l:str = substitute(l:str, ' \+', ' ', 'g')
+                let l:str = substitute(l:str, '^\s*\(.\{-}\)\s*$', '\1', '')
+
+                call ale#util#Echo(l:str)
+            endif
+        endif
+    endif
+endfunction
+
+function! s:ShowDetails(linter) abort
+    let l:buffer = bufnr('')
+    let [l:line, l:column] = getcurpos()[1:2]
+
+    let l:Callback = a:linter.lsp is# 'tsserver'
+    \   ? function('ale#hover#HandleTSServerResponse')
+    \   : function('ale#hover#HandleLSPResponse')
+
+    let l:lsp_details = ale#linter#StartLSP(l:buffer, a:linter, l:Callback)
+
+    if empty(l:lsp_details)
+        return 0
+    endif
+
+    let l:id = l:lsp_details.connection_id
+    let l:root = l:lsp_details.project_root
+
+    if a:linter.lsp is# 'tsserver'
+        " TODO: Implement this.
+        return
+    else
+        " Send a message saying the buffer has changed first, or the
+        " hover position probably won't make sense.
+        call ale#lsp#Send(l:id, ale#lsp#message#DidChange(l:buffer), l:root)
+
+        let l:column = min([l:column, len(getline(l:line))])
+
+        let l:message = ale#lsp#message#Hover(l:buffer, l:line, l:column)
+    endif
+
+    let l:request_id = ale#lsp#Send(l:id, l:message, l:root)
+
+    let s:hover_map[l:request_id] = {
+    \   'buffer': l:buffer,
+    \   'line': l:line,
+    \   'column': l:column,
+    \}
+endfunction
+
+function! ale#hover#Show() abort
+    for l:linter in ale#linter#Get(&filetype)
+        if !empty(l:linter.lsp) && l:linter.lsp isnot# 'tsserver'
+            call s:ShowDetails(l:linter)
+        endif
+    endfor
+endfunction

autoload/ale/lsp/message.vim

@@ -126,3 +126,12 @@ function! ale#lsp#message#References(buffer, line, column) abort
     \   'context': {'includeDeclaration': v:false},
     \}]
 endfunction
+
+function! ale#lsp#message#Hover(buffer, line, column) abort
+    return [0, 'textDocument/hover', {
+    \   'textDocument': {
+    \       'uri': ale#path#ToURI(expand('#' . a:buffer . ':p')),
+    \   },
+    \   'position': {'line': a:line - 1, 'character': a:column},
+    \}]
+endfunction

autoload/ale/util.vim

@@ -11,6 +11,11 @@ function! ale#util#FeedKeys(...) abort
     return call('feedkeys', a:000)
 endfunction
 
+" A wrapper function for echo so we can test calls for it.
+function! ale#util#Echo(string) abort
+    execute 'echo a:string'
+endfunction
+
 " A wrapper function for execute, so we can test executing some commands.
 function! ale#util#Execute(expr) abort
     execute a:expr