Various previewer fixes (#260)

- Set env vars for previewer with set_env({ key = value } fix #228)
- Set pager for git previewes (default is GIT_PAGER=less so users can scroll see #253)
- Use less for people who don't have bat but less installed
- Reset less env to only '-RS' because '-X' will break scrolling(fix #253, thanks @eth3lbert)
- Scrolling for buffer previewer(thanks @tami5 for helping)
  - Also new function to create buffer previewers (which has scrolling by default). Used for tags and help_tags previewer.
- Add new setting set_env to readme

3 files changed, 129 insertions, 53 deletions

diff --git a/README.md b/README.md
index eb0fb46..bfeb398 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ with advanced features.  It is written in `lua` and is built on top of latest
 awesome features from `neovim` core.  `Telescope.nvim` is centered around
 modularity so much so that each picker is its own world, (meaning it can be
 configured in isolation from other pickers, such presentation, algorithm,
-mappings ... etc).  
+mappings ... etc).
 
 `Telescope.nvim` was built with the intention of becoming a library, but it has long grown to
 be much bigger than that.  In addition to
@@ -23,7 +23,7 @@ growing number of community driven [built-in pickers](#built-in-pickers),
 covering a wide range of use cases and tools, and offers a customizable user
 interface.
 
- 
+
 <!-- You can read this documentation from start to finish, or you can look at the -->
 <!-- outline and directly jump to the section that interests you most. -->
 
@@ -44,7 +44,7 @@ This section should guide to run your first built-in pickers :smile:
 [Neovim Nightly (0.5)](https://github.com/neovim/neovim/releases/tag/nightly)
   is required for `telescope.nvim` to work.
 
-#### Optional dependences 
+#### Optional dependences
 - [sharkdp/bat](https://github.com/sharkdp/bat) (preview)
 - [sharkdp/fd](https://github.com/sharkdp/fd) (finder)
 - [BurntSushi/ripgrep](https://github.com/BurntSushi/ripgrep) (finder)
@@ -72,7 +72,7 @@ call dein#add('nvim-telescope/telescope.nvim')
 ```
 Using [packer.nvim](https://github.com/wbthomason/packer.nvim)
 
-```lua 
+```lua
 use {
   'nvim-telescope/telescope.nvim',
   requires = {{'nvim-lua/popup.nvim'}, {'nvim-lua/plenary.nvim'}}
@@ -108,7 +108,7 @@ This section should help you explore available options to configure and
 customize your `telescope.nvim`.
 
 Unlike most vim plugins, `telescope.nvim` can be customized either by applying
-customizations globally or individual pre picker. 
+customizations globally or individual pre picker.
 
 - **Global Customization** affecting all pickers can be done through the
   main `setup()` method (see defaults below)
@@ -125,12 +125,12 @@ As an example of using the `setup()` method, the following code configures
 require('telescope').setup{
   defaults = {
     vimgrep_arguments = {
-      'rg', 
-      '--color=never', 
-      '--no-heading', 
-      '--with-filename', 
-      '--line-number', 
-      '--column', 
+      'rg',
+      '--color=never',
+      '--no-heading',
+      '--with-filename',
+      '--line-number',
+      '--column',
       '--smart-case'
     },
     prompt_position = "bottom",
@@ -154,6 +154,7 @@ require('telescope').setup{
     borderchars = { '─', '│', '─', '│', '╭', '╮', '╯', '╰'},
     color_devicons = true,
     use_less = true,
+    set_env = { ['COLORTERM'] = 'truecolor' }, -- default { }, currently unsupported for shells like cmd.exe / powershell.exe
   }
 }
 ```
@@ -186,9 +187,10 @@ EOF
 | `preview_cutoff`       | TODO                                                  | NUM                        |
 | `results_height`       | TODO                                                  | NUM                        |
 | `results_width`        | TODO                                                  | NUM                        |
-| `borderchars`          | The border chars, it gives border telescope window    | dict                       | 
+| `borderchars`          | The border chars, it gives border telescope window    | dict                       |
 | `color_devicons`       | Whether to color devicons or not                      | boolean                    |
-| `use_less`             | Whether to use less of cat/bat                        | boolean                    |
+| `use_less`             | Whether to use less with bat or less/cat if bat not installed | boolean                    |
+| `set_env`              | Set environment variables for previewer               | dict                       |
 | `scroll_strategy`      | How to behave when the when there are no more item next/prev | cycle, nil          |
 
 #### Options affecting Sorting
@@ -198,8 +200,8 @@ EOF
 | `file_sorter`          | The sorter for file lists.                            | [Sorters](#built-in-sorters)   |
 | `generic_sorter`       | The sorter for everything else.                       | [Sorters](#built-in-sorters)   |
 | `vimgrep_arguments`    | The command line argument for grep search ... TODO.   | dict                       |
-| `selection_strategy`   | What happens to the selection if the list changes.    | follow/reset/row           | 
-| `file_ignore_patterns` | Pattern to be ignored `{ "scratch/.*", "%.env"}`      | dict                       | 
+| `selection_strategy`   | What happens to the selection if the list changes.    | follow/reset/row           |
+| `file_ignore_patterns` | Pattern to be ignored `{ "scratch/.*", "%.env"}`      | dict                       |
 | `shorten_path`         | Whether to shorten paths or not.                      | boolean                    |
 
 #### Mappings
@@ -222,7 +224,7 @@ Many familiar mapping patterns are setup as defaults.
 | `<Esc>`        | close telescope (in normal mode) |
 
 To see the full list of mappings, check out `lua/telescope/mappings.lua` and
-the `default_mappings` table.  
+the `default_mappings` table.
 
 
 Much like [built-in pickers](#built-in-pickers), there are a number of
@@ -273,7 +275,7 @@ require('telescope').setup{
 For a [picker](#built-in-pickers) specific remapping, it can be done by setting
 its `attach_mappings` key to a function, like this
 
-```lua 
+```lua
 local actions = require('telescope.actions')
 -- Picker specific remapping
 ------------------------------
@@ -382,7 +384,7 @@ Built-in function ready to be bound to any key you like :smile:.
 | ..................................  | Your next awesome finder function here :D                        |
 
 
-#### Built-in Sorters 
+#### Built-in Sorters
 
 | Sorters                            | Description                                                     |
 |------------------------------------|-----------------------------------------------------------------|
@@ -406,7 +408,7 @@ return a number, which is equivalent to the "distance" between the current
 ## Built-in Themes
 
 Common groups of settings can be set up to allow for themes.
-We have some built in themes but are looking for more cool options. 
+We have some built in themes but are looking for more cool options.
 
 | Themes                   | Description                                                           |
 |--------------------------|-----------------------------------------------------------------------|
@@ -425,7 +427,7 @@ Themes should work with every `telescope.builtin` function.  If you wish to
 make theme, check out `lua/telescope/themes.lua`. If you need more features,
 make an issue :).
 
-## API 
+## API
 <!-- TODO: need to provide working examples for every api -->
 
 #### Finders
@@ -441,9 +443,9 @@ Finder:new{
 ```
 
 #### Picker
-<!-- TODO: this section need some love, an in-depth explanation will be appreciated it need some in depth explanation --> 
+<!-- TODO: this section need some love, an in-depth explanation will be appreciated it need some in depth explanation -->
 <!-- TODO what is pickers -->
-This section is an overview of how custom pickers can be created any configured. 
+This section is an overview of how custom pickers can be created any configured.
 
 
 ```lua
@@ -508,19 +510,19 @@ All `telescope.nvim` functions are wrapped in `vim` commands for easy access, it
 supports tab completions and settings options.
 
 ```viml
-" Tab completion 
-:Telescope |<tab> 
+" Tab completion
+:Telescope |<tab>
 :Telescope find_files
 
 " Setting options
-:Telescope find_files prompt_prefix=🔍 
+:Telescope find_files prompt_prefix=🔍
 
 " If option is table type in lua code ,you can use `,` connect each command string eg:
 " find_command,vimgrep_arguments they are both table type. so config it in commandline like
 :Telecope find_files find_command=rg,--ignore,--hidden,--files prompt_prefix=🔍
 ```
 
-## Media 
+## Media
 
 - [What is Telescope? (Video)](https://www.twitch.tv/teej_dv/clip/RichDistinctPlumberPastaThat)
 - [More advanced configuration (Video)](https://www.twitch.tv/videos/756229115)
@@ -533,11 +535,11 @@ supports tab completions and settings options.
 
 All options available from the setup function (see [Configuration options]()) and
 some other functions can be easily changed in custom pickers or built-in
-functions. 
+functions.
 <!-- TODO: insert a list of available options like previewer and prompt prefix -->
 
-```lua 
--- Disable preview for find files 
+```lua
+-- Disable preview for find files
 nnoremap <leader>ff :lua require('telescope.builtin').find_files({previewer = false})<CR>
 
 -- Change change prompt prefix for find_files builtin function:
diff --git a/lua/telescope/config.lua b/lua/telescope/config.lua
index 5e3212a..1d795c6 100644
--- a/lua/telescope/config.lua
+++ b/lua/telescope/config.lua
@@ -62,10 +62,12 @@ function config.set_defaults(defaults)
   set("use_less", true)
   set("color_devicons", true)
 
+  set("set_env", {})
+
   -- TODO: Add motions to keybindings
 
   -- To disable a keymap, put [map] = false
-  --        So, to not map "<C-n>", just put 
+  --        So, to not map "<C-n>", just put
   --
   --            ...,
   --            ["<C-n>"] = false,
diff --git a/lua/telescope/previewers.lua b/lua/telescope/previewers.lua
index 9898079..01d8793 100644
--- a/lua/telescope/previewers.lua
+++ b/lua/telescope/previewers.lua
@@ -20,6 +20,19 @@ Previewer.__index = Previewer
 -- TODO: Should play with these some more, ty @clason
 local bat_options = {"--style=plain", "--color=always", "--paging=always"}
 local has_less = (vim.fn.executable('less') == 1) and config.values.use_less
+local termopen_env = vim.tbl_extend("force", { ['GIT_PAGER'] = (has_less and 'less' or ''), LESS = '-RS' }, config.values.set_env)
+
+-- TODO(conni2461): Workaround for neovim/neovim#11751. Add only quotes when using else branch.
+local valuate_shell = function()
+  local shell = vim.o.shell
+  if string.find(shell, 'powershell.exe') or string.find(shell, 'cmd.exe') then
+    return ''
+  else
+    return "'"
+  end
+end
+
+local add_quotes = valuate_shell()
 
 local get_file_stat = function(filename)
   return vim.loop.fs_stat(vim.fn.expand(filename)) or {}
@@ -39,9 +52,9 @@ local bat_maker = function(filename, lnum, start, finish)
 
   if has_less then
     if start then
-      table.insert(command, {"--pager", string.format("less -RS +%s", start)})
+      table.insert(command, {"--pager", string.format("%sless +%s%s", add_quotes, start, add_quotes)})
     else
-      table.insert(command, {"--pager", "less -RS"})
+      table.insert(command, {"--pager", "less"})
     end
   else
     if start and finish then
@@ -54,14 +67,14 @@ local bat_maker = function(filename, lnum, start, finish)
   end
 
   return flatten {
-    command, bat_options, "--", vim.fn.expand(filename)
+    command, bat_options, "--", add_quotes .. vim.fn.expand(filename) .. add_quotes
   }
 end
 
 -- TODO: Add other options for cat to do this better
-local cat_maker = function(filename, _, _, _)
+local cat_maker = function(filename, _, start, _)
   if get_file_stat(filename).type == 'directory' then
-    return { 'ls', '-la', vim.fn.expand(filename) }
+    return { 'ls', '-la', add_quotes .. vim.fn.expand(filename) .. add_quotes }
   end
 
   if 1 == vim.fn.executable('file') then
@@ -72,9 +85,17 @@ local cat_maker = function(filename, _, _, _)
     end
   end
 
-  return {
-    "cat", "--", vim.fn.expand(filename)
-  }
+  if has_less then
+    if start then
+      return { 'less', string.format('+%s', start), add_quotes .. vim.fn.expand(filename) .. add_quotes }
+    else
+      return { 'less', add_quotes .. vim.fn.expand(filename) .. add_quotes }
+    end
+  else
+    return {
+      "cat", "--", add_quotes .. vim.fn.expand(filename) .. add_quotes
+    }
+  end
 end
 
 local get_maker = function(opts)
@@ -167,6 +188,41 @@ previewers.new = function(...)
   return Previewer:new(...)
 end
 
+previewers.new_buffer_previewer = function(opts)
+  opts = opts or {}
+
+  assert(opts.preview_fn, "preview_fn is required function")
+
+  if not opts.scroll_fn then
+    function opts.scroll_fn(self, direction)
+      local input = direction > 0 and "d" or "u"
+      local count = math.abs(direction)
+
+      self:send_input({ count = count, input = input })
+    end
+  end
+
+  if not opts.send_input then
+    function opts.send_input(self, input)
+      if not self.state then
+        return
+      end
+
+      local bufnr = vim.api.nvim_win_get_buf(self.state.hl_win)
+      local max_line = vim.fn.getbufinfo(bufnr)[1].linecount
+      local line = vim.api.nvim_win_get_cursor(self.state.hl_win)[1]
+      if input.input == 'u' then
+        line = (line - input.count) > 0 and (line - input.count) or 1
+      else
+        line = (line + input.count) <= max_line and (line + input.count) or max_line
+      end
+      vim.api.nvim_win_set_cursor(self.state.hl_win, { line, 1 })
+    end
+  end
+
+  return Previewer:new(opts)
+end
+
 previewers.new_termopen_previewer = function(opts)
   opts = opts or {}
 
@@ -234,13 +290,25 @@ previewers.new_termopen_previewer = function(opts)
 
     local term_opts = {
       cwd = opts.cwd or vim.fn.getcwd(),
+      env = termopen_env
     }
 
+    -- TODO(conni2461): Workaround for neovim/neovim#11751.
+    local get_cmd = function(status)
+      local shell = vim.o.shell
+      if string.find(shell, 'powershell.exe') or string.find(shell, 'cmd.exe') then
+        return opts.get_command(entry, status)
+      else
+        local env = {}
+        for k, v in pairs(termopen_env) do
+          table.insert(env, k .. '=' .. v)
+        end
+        return table.concat(env, ' ') .. ' ' .. table.concat(opts.get_command(entry, status), ' ')
+      end
+    end
+
     with_preview_window(status, bufnr, function()
-      set_term_id(
-        self,
-        vim.fn.termopen(opts.get_command(entry, status), term_opts)
-      )
+      set_term_id(self, vim.fn.termopen(get_cmd(status), term_opts))
     end)
 
     vim.api.nvim_buf_set_name(bufnr, tostring(bufnr))
@@ -274,7 +342,7 @@ previewers.new_termopen_previewer = function(opts)
 end
 
 previewers.vim_buffer = defaulter(function(_)
-  return previewers.new {
+  return previewers.new_buffer_previewer {
     setup = function()
       return {
         last_set_bufnr = nil
@@ -333,6 +401,7 @@ previewers.vim_buffer = defaulter(function(_)
         -- print("LNUM:", entry.lnum)
       end
 
+      vim.api.nvim_win_set_option(status.preview_win, 'scrolloff', 999)
       log.info("Previewed bufnr", bufnr)
     end,
   }
@@ -342,7 +411,7 @@ previewers.git_commit_diff = defaulter(function(_)
   return previewers.new_termopen_previewer {
     get_command = function(entry)
       local sha = entry.value
-      return { 'git', '--no-pager', 'diff', sha .. '^!' }
+      return { 'git', '-p', 'diff', sha .. '^!' }
     end
   }
 end, {})
@@ -350,8 +419,8 @@ end, {})
 previewers.git_branch_log = defaulter(function(_)
   return previewers.new_termopen_previewer {
     get_command = function(entry)
-      return { 'git', 'log', '--graph',
-               '--pretty=format:%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr)%Creset',
+      return { 'git', '-p', 'log', '--graph',
+               "--pretty=format:" .. add_quotes .. "%Cred%h%Creset -%C(yellow)%d%Creset %s %Cgreen(%cr)%Creset" .. add_quotes,
                '--abbrev-commit', '--date=relative', entry.value }
     end
   }
@@ -360,7 +429,7 @@ end, {})
 previewers.git_file_diff = defaulter(function(_)
   return previewers.new_termopen_previewer {
     get_command = function(entry)
-      return { 'git', '--no-pager', 'diff', entry.value }
+      return { 'git', '-p', 'diff', entry.value }
     end
   }
 end, {})
@@ -400,8 +469,8 @@ previewers.vimgrep = defaulter(function(opts)
   }
 end, {})
 
-previewers.ctags = defaulter(function(opts)
-  return previewers.new {
+previewers.ctags = defaulter(function(_)
+  return previewers.new_buffer_previewer {
     setup = function()
       return {}
     end,
@@ -428,10 +497,10 @@ previewers.ctags = defaulter(function(opts)
         vim.api.nvim_win_set_option(status.preview_win, 'winhl', 'Normal:Normal')
         vim.api.nvim_win_set_option(status.preview_win, 'signcolumn', 'no')
         vim.api.nvim_win_set_option(status.preview_win, 'foldlevel', 100)
+        vim.api.nvim_win_set_option(status.preview_win, 'scrolloff', 999)
 
         pcall(vim.fn.matchdelete, self.state.hl_id, self.state.hl_win)
         vim.fn.search(scode)
-        vim.cmd "norm zz"
 
         self.state.hl_win = status.preview_win
         self.state.hl_id = vim.fn.matchadd('Search', scode)
@@ -469,7 +538,7 @@ previewers.qflist = defaulter(function(opts)
 end, {})
 
 previewers.help = defaulter(function(_)
-  return previewers.new {
+  return previewers.new_buffer_previewer {
     setup = function()
       return {}
     end,
@@ -542,9 +611,12 @@ previewers.help = defaulter(function(_)
 
         log.trace([[lua vim.fn.search("]], search_query, [[")]])
 
+        -- Clear previous search
+        pcall(vim.fn.matchdelete, self.state.hl_id, self.state.hl_win)
         vim.cmd "norm! gg"
         vim.fn.search(search_query, "W")
-        vim.cmd "norm  zt"
+
+        vim.api.nvim_win_set_option(status.preview_win, 'scrolloff', 999)
 
         self.state.hl_win = status.preview_win
         self.state.hl_id = vim.fn.matchadd('Search', search_query)
@@ -681,7 +753,7 @@ previewers.man = defaulter(function(_)
 end)
 
 previewers.display_content = defaulter(function(_)
-  return previewers.new {
+  return previewers.new_buffer_previewer {
     preview_fn = function(self, entry, status)
       with_preview_window(status, nil, function()
         local bufnr = vim.fn.bufadd("Preview command")