feat(shfmt): add automatic indentation detection (nvim-lua#481)

* feat(shfmt): automatically detect indentation

* fix(markdown-toc): improve correctness of indentation size calculation

* fix(djlint): improve correctness of indentation size calculation

* feat: add effective `shiftwidth` to `conform.Context`

this also refactors formatters that automatically set indentation level
to use the new shiftwidth context

Author: mehalter

lua/conform/formatters/djlint.lua

@@ -7,8 +7,7 @@ return {
   },
   command = "djlint",
   args = function(_, ctx)
-    local indent = vim.bo[ctx.buf].tabstop or 4 -- default is 4
-    return { "--reformat", "--indent", indent, "-" }
+    return { "--reformat", "--indent", ctx.shiftwidth, "-" }
   end,
   cwd = util.root_file({
     ".djlintrc",

lua/conform/formatters/markdown-toc.lua

@@ -6,10 +6,10 @@ return {
   },
   command = "markdown-toc",
   stdin = false,
-  args = function(self, ctx)
+  args = function(_, ctx)
     -- use the indentation set in the current buffer, effectively allowing us to
     -- use values from .editorconfig
-    local indent = vim.bo[ctx.buf].expandtab and (" "):rep(vim.bo[ctx.buf].tabstop) or "\t"
+    local indent = vim.bo[ctx.buf].expandtab and (" "):rep(ctx.shiftwidth) or "\t"
     return { "--indent=" .. indent, "-i", "$FILENAME" }
   end,
 }

lua/conform/formatters/shfmt.lua

@@ -5,5 +5,11 @@ return {
     description = "A shell parser, formatter, and interpreter with `bash` support.",
   },
   command = "shfmt",
-  args = { "-filename", "$FILENAME" },
+  args = function(_, ctx)
+    local args = { "-filename", "$FILENAME" }
+    if vim.bo[ctx.buf].expandtab then
+      vim.list_extend(args, { "-i", ctx.shiftwidth })
+    end
+    return args
+  end,
 }

lua/conform/runner.lua

@@ -450,6 +450,11 @@ M.build_context = function(bufnr, config, range)
   end
   local filename = vim.api.nvim_buf_get_name(bufnr)
 
+  local shiftwidth = vim.bo[bufnr].shiftwidth
+  if shiftwidth == 0 then
+    shiftwidth = vim.bo[bufnr].tabstop
+  end
+
   -- Hack around checkhealth. For buffers that are not files, we need to fabricate a filename
   if vim.bo[bufnr].buftype ~= "" then
     filename = ""
@@ -482,6 +487,7 @@ M.build_context = function(bufnr, config, range)
     filename = filename,
     dirname = dirname,
     range = range,
+    shiftwidth = shiftwidth,
   }
 end
 

lua/conform/types.lua

@@ -49,6 +49,7 @@
 ---@field filename string
 ---@field dirname string
 ---@field range? conform.Range
+---@field shiftwidth integer
 
 ---@class (exact) conform.RangeContext : conform.Context
 ---@field range conform.Range

tests/runner_spec.lua

@@ -59,11 +59,36 @@ describe("runner", function()
       local config = assert(conform.get_formatter_config("test"))
       local ctx = runner.build_context(0, config)
       local filename = vim.api.nvim_buf_get_name(bufnr)
-      assert.are.same({
-        buf = bufnr,
-        filename = filename,
-        dirname = vim.fs.dirname(filename),
-      }, ctx)
+      assert.equal(bufnr, ctx.buf)
+      assert.equal(filename, ctx.filename)
+      assert.equal(vim.fs.dirname(filename), ctx.dirname)
+    end)
+
+    it("sets the shiftwidth to shiftwidth", function()
+      vim.cmd.edit({ args = { "README.md" } })
+      local bufnr = vim.api.nvim_get_current_buf()
+      vim.bo[bufnr].shiftwidth = 7
+      conform.formatters.test = {
+        meta = { url = "", description = "" },
+        command = "echo",
+      }
+      local config = assert(conform.get_formatter_config("test"))
+      local ctx = runner.build_context(0, config)
+      assert.equal(7, ctx.shiftwidth)
+    end)
+
+    it("sets the shiftwidth to tabstop as fallback", function()
+      vim.cmd.edit({ args = { "README.md" } })
+      local bufnr = vim.api.nvim_get_current_buf()
+      vim.bo[bufnr].shiftwidth = 0
+      vim.bo[bufnr].tabstop = 3
+      conform.formatters.test = {
+        meta = { url = "", description = "" },
+        command = "echo",
+      }
+      local config = assert(conform.get_formatter_config("test"))
+      local ctx = runner.build_context(0, config)
+      assert.equal(3, ctx.shiftwidth)
     end)
 
     it("sets temp file when stdin = false", function()