test(babel): cover shebang and tangle-mode file permissions

Add Plenary specs to verify shebang prepending, default 0755 behavior,
and :tangle-mode parsing/override (octal, chmod, ls styles).

Author: SjB

tests/plenary/babel/tangle_shebang_mode_spec.lua

@@ -0,0 +1,102 @@
+local helpers = require('tests.plenary.helpers')
+
+local function stat_mode(path)
+  local st = vim.uv.fs_stat(path)
+  assert.is_not_nil(st)
+  -- libuv returns st.mode containing type bits + permission bits
+  return bit.band(st.mode, 0x1FF)
+end
+
+describe('Tangle (shebang & mode)', function()
+  it('should prepend shebang and default to 0755 when :shebang is set', function()
+    local file = helpers.create_file({
+      '#+property: header-args :tangle yes',
+      '* Headline',
+      "#+begin_src sh :shebang '#!/usr/bin/env bash'",
+      'echo "hi"',
+      '#+end_src',
+    })
+
+    vim.cmd('norm ,obt')
+
+    local tangled_file = vim.fn.fnamemodify(file.filename, ':r') .. '.sh'
+    assert.is.Not.Nil(vim.uv.fs_stat(tangled_file))
+    assert.are.same({
+      '#!/usr/bin/env bash',
+      'echo "hi"',
+    }, vim.fn.readfile(tangled_file))
+
+    assert.are.equal(tonumber("0755", 8), stat_mode(tangled_file))
+  end)
+
+  it('should apply :tangle-mode octal form (o644) when provided', function()
+    local file = helpers.create_file({
+      '#+property: header-args :tangle yes',
+      '* Headline',
+      "#+begin_src lua :tangle-mode 'o644'",
+      'print("hi")',
+      '#+end_src',
+    })
+
+    vim.cmd('norm ,obt')
+
+    local tangled_file = vim.fn.fnamemodify(file.filename, ':r') .. '.lua'
+    assert.is.Not.Nil(vim.uv.fs_stat(tangled_file))
+    assert.are.equal(tonumber("0644", 8), stat_mode(tangled_file))
+  end)
+
+  it('should apply :tangle-mode chmod style (u=rw,go=r) when provided', function()
+    local file = helpers.create_file({
+      '#+property: header-args :tangle yes',
+      '* Headline',
+      "#+begin_src lua :tangle-mode 'u=rw,go=r'",
+      'print("hi")',
+      '#+end_src',
+    })
+
+    vim.cmd('norm ,obt')
+
+    local tangled_file = vim.fn.fnamemodify(file.filename, ':r') .. '.lua'
+    assert.is.Not.Nil(vim.uv.fs_stat(tangled_file))
+    assert.are.equal(tonumber("0644", 8), stat_mode(tangled_file))
+  end)
+
+  it('should apply :tangle-mode ls style (rwxr-x---) when provided', function()
+    local file = helpers.create_file({
+      '#+property: header-args :tangle yes',
+      '* Headline',
+      "#+begin_src lua :tangle-mode 'rwxr-x---'",
+      'print("hi")',
+      '#+end_src',
+    })
+
+    vim.cmd('norm ,obt')
+
+    local tangled_file = vim.fn.fnamemodify(file.filename, ':r') .. '.lua'
+    assert.is.Not.Nil(vim.uv.fs_stat(tangled_file))
+    assert.are.equal(tonumber("0750", 8), stat_mode(tangled_file))
+  end)
+
+  it('should keep 0755 when :shebang is set even if :tangle-mode is also set (mode is overridden if :tangle-mode present)', function()
+    local file = helpers.create_file({
+      '#+property: header-args :tangle yes',
+      '* Headline',
+      "#+begin_src sh :shebang '#!/usr/bin/env bash' :tangle-mode 'o700'",
+      'echo "hi"',
+      '#+end_src',
+    })
+
+    vim.cmd('norm ,obt')
+
+    local tangled_file = vim.fn.fnamemodify(file.filename, ':r') .. '.sh'
+    assert.is.Not.Nil(vim.uv.fs_stat(tangled_file))
+
+    assert.are.same({
+      '#!/usr/bin/env bash',
+      'echo "hi"',
+    }, vim.fn.readfile(tangled_file))
+
+    -- :tangle-mode should override the shebang default
+    assert.are.equal(tonumber("0700", 8), stat_mode(tangled_file))
+  end)
+end)