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

6 files changed, 108 insertions, 7 deletions

diff --git a/README.md b/README.md
index 027a7ce..2ff572b 100644
--- a/README.md
+++ b/README.md
@@ -464,7 +464,7 @@ require("conform").setup({
       -- Return a single string instead of a list to run the command in a shell
       args = { "--stdin-from-filename", "$FILENAME" },
       -- If the formatter supports range formatting, create the range arguments here
-      range_args = function(ctx)
+      range_args = function(self, ctx)
         return { "--line-start", ctx.range.start[1], "--line-end", ctx.range["end"][1] }
       end,
       -- Send file contents to stdin, read new contents from stdout (default true)
@@ -478,7 +478,7 @@ require("conform").setup({
       -- When stdin=false, use this template to generate the temporary file that gets formatted
       tmpfile_format = ".conform.$RANDOM.$FILENAME",
       -- When returns false, the formatter will not be used
-      condition = function(ctx)
+      condition = function(self, ctx)
         return vim.fs.basename(ctx.filename) ~= "README.md"
       end,
       -- Exit codes that indicate success (default { 0 })
diff --git a/doc/conform.txt b/doc/conform.txt
index a7aed2a..977a0f0 100644
--- a/doc/conform.txt
+++ b/doc/conform.txt
@@ -61,7 +61,7 @@ OPTIONS                                                          *conform-option
           -- Return a single string instead of a list to run the command in a shell
           args = { "--stdin-from-filename", "$FILENAME" },
           -- If the formatter supports range formatting, create the range arguments here
-          range_args = function(ctx)
+          range_args = function(self, ctx)
             return { "--line-start", ctx.range.start[1], "--line-end", ctx.range["end"][1] }
           end,
           -- Send file contents to stdin, read new contents from stdout (default true)
@@ -75,7 +75,7 @@ OPTIONS                                                          *conform-option
           -- When stdin=false, use this template to generate the temporary file that gets formatted
           tmpfile_format = ".conform.$RANDOM.$FILENAME",
           -- When returns false, the formatter will not be used
-          condition = function(ctx)
+          condition = function(self, ctx)
             return vim.fs.basename(ctx.filename) ~= "README.md"
           end,
           -- Exit codes that indicate success (default { 0 })
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 == "$RELATIVE_FILEPATH" then
+        v = relative_filename
       end
       table.insert(cmd, v)
     end
diff --git a/scripts/options_doc.lua b/scripts/options_doc.lua
index 96c0f2b..3e22802 100644
--- a/scripts/options_doc.lua
+++ b/scripts/options_doc.lua
@@ -48,7 +48,7 @@ require("conform").setup({
       -- Return a single string instead of a list to run the command in a shell
       args = { "--stdin-from-filename", "$FILENAME" },
       -- If the formatter supports range formatting, create the range arguments here
-      range_args = function(ctx)
+      range_args = function(self, ctx)
         return { "--line-start", ctx.range.start[1], "--line-end", ctx.range["end"][1] }
       end,
       -- Send file contents to stdin, read new contents from stdout (default true)
@@ -62,7 +62,7 @@ require("conform").setup({
       -- When stdin=false, use this template to generate the temporary file that gets formatted
       tmpfile_format = ".conform.$RANDOM.$FILENAME",
       -- When returns false, the formatter will not be used
-      condition = function(ctx)
+      condition = function(self, ctx)
         return vim.fs.basename(ctx.filename) ~= "README.md"
       end,
       -- Exit codes that indicate success (default { 0 })
diff --git a/tests/fs_spec.lua b/tests/fs_spec.lua
new file mode 100644
index 0000000..2d788c9
--- /dev/null
+++ b/tests/fs_spec.lua
@@ -0,0 +1,22 @@
+local fs = require("conform.fs")
+
+describe("fs", function()
+  local relative_paths = {
+    { "/home", "/home/file.txt", "file.txt" },
+    { "/home/", "/home/file.txt", "file.txt" },
+    { "/home", "/foo/file.txt", "../foo/file.txt" },
+    { "/home/foo", "/home/bar/file.txt", "../bar/file.txt" },
+    { "/home", "/file.txt", "../file.txt" },
+    { "/home", "/home/foo/file.txt", "foo/file.txt" },
+    { ".", "foo/file.txt", "foo/file.txt" },
+    { "home", "home/file.txt", "file.txt" },
+    { "home", "file.txt", "../file.txt" },
+  }
+
+  it("relative_path", function()
+    for _, paths in ipairs(relative_paths) do
+      local source, target, expected = unpack(paths)
+      assert.are.same(fs.relative_path(source, target), expected)
+    end
+  end)
+end)