fix(utils): swap_nodes calculates correct char_delta (#4110)

* fix(utils): swap_nodes calculates correct char_delta

The char_delta is not calculated correctly right now when there are two
treesitter nodes being swapped, one directly following the other. This
is rare but can happen for example when attempting to swap "print" and
"(1)" in "print(1)". In this case an incorrect char_delta is calculated
because of a bug in range comparison.

* test(swap_nodes): check cursor

* add a regression test (for multiline node swap)
* add a test with adjacent swaps that fails when char_delta is not
  calculated correctly

* test(swap_nodes): check text content after swap

* test: note language for parser

* fix tests

* use same not equal for table comparison

tests/unit/ts_utils_spec.lua

@@ -106,3 +106,43 @@ describe("update_selection", function()
     )
   end)
 end)
+
+describe("swap_nodes", function()
+  local function swap(case)
+    vim.api.nvim_buf_set_lines(0, 0, -1, false, case.lines)
+    vim.opt.filetype = case.filetype
+    local a = vim.treesitter.get_node_at_pos(0, case.a[1], case.a[2], {})
+    local b = vim.treesitter.get_node_at_pos(0, case.b[1], case.b[2], {})
+    tsutils.swap_nodes(a, b, 0, true)
+  end
+
+  it("works on adjacent nodes", function()
+    swap {
+      filetype = "python",
+      lines = { "print(1)" },
+      a = { 0, 0 },
+      b = { 0, 5 },
+    }
+
+    it("swaps text", function() end)
+    assert.same(vim.api.nvim_buf_get_lines(0, 0, -1, false), { "(1)print" })
+
+    it("moves the cursor", function() end)
+    assert.same(vim.api.nvim_win_get_cursor(0), { 1, 3 })
+  end)
+
+  it("works with multiline nodes", function()
+    swap {
+      filetype = "lua",
+      lines = { "x = { [[", "]], [[", ".....]]}" },
+      a = { 0, 6 },
+      b = { 1, 4 },
+    }
+
+    it("swaps text", function() end)
+    assert.same(vim.api.nvim_buf_get_lines(0, 0, -1, false), { "x = { [[", ".....]], [[", "]]}" })
+
+    it("moves the cursor", function() end)
+    assert.same(vim.api.nvim_win_get_cursor(0), { 2, 9 })
+  end)
+end)