Initial implementation

lua/hflip.lua

@@ -0,0 +1,55 @@
+local function split_ext(path)
+    return path:match('^(.+)(%..+)$')
+end
+
+local function file_exists(path)
+    return vim.loop.fs_stat(path) ~= nil
+end
+
+local function locate_flip_path(name, exts)
+    for key, _ in pairs(exts) do
+        local path = name .. key
+        if file_exists(path) then
+            return path
+        end
+
+        local path_upper = name .. key:upper()
+        if file_exists(path_upper) then
+            return path_upper
+        end
+    end
+end
+
+local function hflip()
+    local header_exts = {
+        ['.h'] = true,
+        ['.hpp'] = true,
+        ['.lua'] = true,
+    }
+
+    local source_exts = {
+        ['.c'] = true,
+        ['.cpp'] = true
+    }
+
+    local index = vim.api.nvim_get_current_buf()
+    local path = vim.api.nvim_buf_get_name(index)
+    local name, ext = split_ext(path)
+
+    ext = ext:lower()
+
+    local flip_path
+    if header_exts[ext] then
+        flip_path = locate_flip_path(name, source_exts)
+    elseif source_exts[ext] then
+        flip_path = locate_flip_path(name, header_exts)
+    end
+
+    if flip_path then
+        vim.api.nvim_exec(string.format('e %s', flip_path), false)
+    end
+end
+
+return {
+    hflip = hflip
+}

plugin/hflip.vim

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+" in plugin/hflip.vim
+if exists('g:loaded_hflip') | finish | endif " prevent loading file twice
+
+let s:save_cpo = &cpo " save user coptions
+set cpo&vim " reset them to defaults
+
+" command to run our plugin
+command! HFlip lua require'hflip'.hflip()
+
+let &cpo = s:save_cpo " and restore after
+unlet s:save_cpo
+
+let g:loaded_hflip = 1