feat: formatters can use $RELATIVE_FILEPATH in args (#349)

2 files changed, 80 insertions, 1 deletions

diff --git a/lua/conform/fs.lua b/lua/conform/fs.lua
index d303dbd..6f92e18 100644
--- a/lua/conform/fs.lua
+++ b/lua/conform/fs.lua
@@ -15,4 +15,72 @@ M.join = function(...)
   return table.concat({ ... }, M.sep)
 end
 
+M.is_absolute = function(path)
+  if M.is_windows then
+    return path:lower():match("^%a:")
+  else
+    return vim.startswith(path, "/")
+  end
+end
+
+M.abspath = function(path)
+  if not M.is_absolute(path) then
+    path = vim.fn.fnamemodify(path, ":p")
+  end
+  return path
+end
+
+--- Returns true if candidate is a subpath of root, or if they are the same path.
+---@param root string
+---@param candidate string
+---@return boolean
+M.is_subpath = function(root, candidate)
+  if candidate == "" then
+    return false
+  end
+  root = vim.fs.normalize(M.abspath(root))
+  -- Trim trailing "/" from the root
+  if root:find("/", -1) then
+    root = root:sub(1, -2)
+  end
+  candidate = vim.fs.normalize(M.abspath(candidate))
+  if M.is_windows then
+    root = root:lower()
+    candidate = candidate:lower()
+  end
+  if root == candidate then
+    return true
+  end
+  local prefix = candidate:sub(1, root:len())
+  if prefix ~= root then
+    return false
+  end
+
+  local candidate_starts_with_sep = candidate:find("/", root:len() + 1, true) == root:len() + 1
+  local root_ends_with_sep = root:find("/", root:len(), true) == root:len()
+
+  return candidate_starts_with_sep or root_ends_with_sep
+end
+
+---Create a relative path from the source to the target
+---@param source string
+---@param target string
+---@return string
+M.relative_path = function(source, target)
+  source = M.abspath(source)
+  target = M.abspath(target)
+  local path = {}
+  while not M.is_subpath(source, target) do
+    table.insert(path, "..")
+    local new_source = vim.fs.dirname(source)
+    assert(source ~= new_source)
+    source = new_source
+  end
+
+  local offset = vim.endswith(source, M.sep) and 1 or 2
+  local rel_target = target:sub(source:len() + offset)
+  table.insert(path, rel_target)
+  return M.join(unpack(path))
+end
+
 return M
diff --git a/lua/conform/runner.lua b/lua/conform/runner.lua
index 0f31e64..b3a1e61 100644
--- a/lua/conform/runner.lua
+++ b/lua/conform/runner.lua
@@ -33,8 +33,17 @@ M.build_cmd = function(formatter_name, ctx, config)
     end
   end
 
+  local cwd
+  if config.cwd then
+    cwd = config.cwd(config, ctx)
+  end
+  local relative_filename = fs.relative_path(cwd or vim.fn.getcwd(), ctx.filename)
+
   if type(args) == "string" then
-    local interpolated = args:gsub("$FILENAME", ctx.filename):gsub("$DIRNAME", ctx.dirname)
+    local interpolated = args
+      :gsub("$FILENAME", ctx.filename)
+      :gsub("$DIRNAME", ctx.dirname)
+      :gsub("$RELATIVE_FILEPATH", relative_filename)
     return command .. " " .. interpolated
   else
     local cmd = { command }
@@ -44,6 +53,8 @@ M.build_cmd = function(formatter_name, ctx, config)
         v = ctx.filename
       elseif v == "$DIRNAME" then
         v = ctx.dirname
+      elseif v == "$RELATIVE_FILEPATH" then
+        v = relative_filename
       end
       table.insert(cmd, v)
     end