fix(path): normalize separators (slashes) #39155

Problem:
Continue separators normalization, and try to keep it at the
nvim <-> external boundary, e.g., `fn.xxx`, `api.xxx`, `:xxx`

Solution:
some key changes
- normalize `$HOME-windows`
- normalize entry points of changing directory
  - `nvim_set_current_dir()`, `chdir()`
- normalize the named pipe
  - `--listen` arg, `--server` arg, `:restart`
  - `serverstart()`, `sockconnect()`, `serverstop()`
- make `expand()` respect 'shellslash' again
- clean up `did_set_shellslash`
- replace `forward_slash` with `TO_SLASH`
- remove obsolete `TMP_PATHSEPSTR`
- remove `slash_adjust` in `do_autocmd_dirchanged`?
- make `fnamemodify()` always return `/` (except when substituting
  separators via `:s`, `:gs` ?)

Note:
- these funcs still apply `slash_adjust` on return, as before:
  `:pwd`, `chdir()`, `exepath()`, `getcwd()`
- these funcs alwarys return `/`, unlike before the normalization PRs
  - `getcompletion()`, `finddir()`, `findfile()`

Also
- clean up code, comments, formatting and tests
- move `TO_SLASH` from `f_chdir` to `changedir_func`
- move `TO_SLASH` from `f_bufadd` to `buflist_new`

Co-authored-by: Justin M. Keyes <justinkz@gmail.com>

test/functional/vimscript/ctx_functions_spec.lua

@@ -322,7 +322,7 @@ describe('context functions', function()
         filter(map(add(
         getjumplist()[0], { 'bufnr': bufnr('%'), 'lnum': getcurpos()[1] }),
         'filter(
-        { "f": expand("#".v:val.bufnr.":p"), "l": v:val.lnum },
+        { "f": expand("#".v:val.bufnr.":p:gs?\\?/?"), "l": v:val.lnum },
         { k, v -> k != "l" || v != 1 })'), '!empty(v:val.f)')
         ]]):gsub('\n', ''))),
       }

test/functional/vimscript/executable_spec.lua

@@ -2,7 +2,7 @@ local t = require('test.testutil')
 local n = require('test.functional.testnvim')()
 
 local eq, clear, call, write_file, command = t.eq, n.clear, n.call, t.write_file, n.command
-local eval = n.eval
+local eval, fn = n.eval, n.fn
 local is_os = t.is_os
 local pcall_err = t.pcall_err
 
@@ -18,38 +18,26 @@ describe('executable()', function()
     eq(1, call('executable', 'false'))
   end)
 
-  if is_os('win') then
-    it('exepath returns consistent slashes #13787', function()
-      -- test/ cannot be a symlink in this test.
-      n.api.nvim_set_current_dir(t.paths.test_source_path)
+  it('exepath respects shellslash #13787', function()
+    t.skip(not is_os('win'), 'N/A for non-Windows')
+    -- test/ cannot be a symlink in this test.
+    n.api.nvim_set_current_dir(t.paths.test_source_path)
 
-      command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
-      eq(
-        [[test/functional/fixtures/bin/null.CMD]],
-        call('fnamemodify', call('exepath', 'null'), ':.')
-      )
-      command('set shellslash')
-      eq(
-        'test/functional/fixtures/bin/null.CMD',
-        call('fnamemodify', call('exepath', 'null'), ':.')
-      )
-    end)
+    command('let $PATH = fnamemodify("./test/functional/fixtures/bin", ":p")')
+    eq(([[%s\test\functional\fixtures\bin\null.CMD]]):format(fn.getcwd()), fn.exepath('null'))
+    command('set shellslash')
+    eq(('%s/test/functional/fixtures/bin/null.CMD'):format(fn.getcwd()), fn.exepath('null'))
+  end)
 
-    it('stdpath returns consistent slashes #13787', function()
-      -- Needs to check paths relative to repo root dir.
-      n.api.nvim_set_current_dir(t.paths.test_source_path)
+  it('stdpath returns consistent slashes #13787', function()
+    t.skip(not is_os('win'), 'N/A for non-Windows')
+    -- Needs to check paths relative to repo root dir.
+    n.api.nvim_set_current_dir(t.paths.test_source_path)
 
-      t.matches(
-        [[build/Xtest_xdg[%w_]*/share/nvim%-data]],
-        call('fnamemodify', call('stdpath', 'data'), ':.')
-      )
-      command('set shellslash')
-      t.matches(
-        'build/Xtest_xdg[%w_]*/share/nvim%-data',
-        call('fnamemodify', call('stdpath', 'data'), ':.')
-      )
-    end)
-  end
+    t.matches('build/Xtest_xdg[%w_]*/share/nvim%-data', fn.stdpath('data'))
+    command('set shellslash')
+    t.matches('build/Xtest_xdg[%w_]*/share/nvim%-data', fn.stdpath('data'))
+  end)
 
   it('fails for invalid values', function()
     for _, input in ipairs({ 'v:null', 'v:true', 'v:false', '{}', '[]' }) do

test/functional/vimscript/fnamemodify_spec.lua

@@ -10,10 +10,6 @@ local write_file = t.write_file
 local is_os = t.is_os
 local chdir = n.fn.chdir
 
-local function eq_slashconvert(expected, got)
-  eq(t.fix_slashes(expected), t.fix_slashes(got))
-end
-
 describe('fnamemodify()', function()
   setup(function()
     write_file('Xtest-fnamemodify.txt', [[foobar]])
@@ -42,7 +38,7 @@ describe('fnamemodify()', function()
       eq(root, fnamemodify([[/]], ':p'))
 
       local letter_colon = root:sub(1, 2)
-      local old_dir = t.fix_slashes(getcwd()) .. '/'
+      local old_dir = ('%s/'):format(getcwd())
       local foo_dir = old_dir .. 'foo/'
       eq(old_dir, fnamemodify(letter_colon, ':p'))
       eq(old_dir, fnamemodify(letter_colon .. '.', ':p'))
@@ -65,28 +61,28 @@ describe('fnamemodify()', function()
     n.api.nvim_set_current_dir(t.paths.test_source_path)
 
     local filename = 'src/version.c'
-    local cwd = getcwd()
+    local cwd = vim.fs.normalize(getcwd())
 
-    eq_slashconvert(cwd .. '/src/version.c', fnamemodify(filename, ':p'))
+    eq(('%s/src/version.c'):format(cwd), fnamemodify(filename, ':p'))
 
-    eq_slashconvert('src/version.c', fnamemodify(filename, ':p:.'))
-    eq_slashconvert(cwd .. '/src', fnamemodify(filename, ':p:h'))
-    eq_slashconvert(cwd .. '', fnamemodify(filename, ':p:h:h'))
+    eq('src/version.c', fnamemodify(filename, ':p:.'))
+    eq(('%s/src'):format(cwd), fnamemodify(filename, ':p:h'))
+    eq(cwd, fnamemodify(filename, ':p:h:h'))
     eq('version.c', fnamemodify(filename, ':p:t'))
-    eq_slashconvert(cwd .. '/src/version', fnamemodify(filename, ':p:r'))
+    eq(('%s/src/version'):format(cwd), fnamemodify(filename, ':p:r'))
 
-    eq_slashconvert(cwd .. '/src/main.c', fnamemodify(filename, ':s?version?main?:p'))
+    eq(('%s/src/main.c'):format(cwd), fnamemodify(filename, ':s?version?main?:p'))
 
     local converted_cwd = cwd:gsub('/', '\\')
     eq(converted_cwd .. '\\src\\version.c', fnamemodify(filename, ':p:gs?/?\\\\?'))
 
     eq('src', fnamemodify(filename, ':h'))
     eq('version.c', fnamemodify(filename, ':t'))
-    eq_slashconvert('src/version', fnamemodify(filename, ':r'))
+    eq('src/version', fnamemodify(filename, ':r'))
     eq('version', fnamemodify(filename, ':t:r'))
     eq('c', fnamemodify(filename, ':e'))
 
-    eq_slashconvert('src/main.c', fnamemodify(filename, ':s?version?main?'))
+    eq('src/main.c', fnamemodify(filename, ':s?version?main?'))
   end)
 
   it('handles advanced examples from ":help filename-modifiers"', function()
@@ -98,11 +94,11 @@ describe('fnamemodify()', function()
 
     eq('c', fnamemodify(filename, ':e:e:r'))
 
-    eq_slashconvert('src/version.c', fnamemodify(filename, ':r'))
+    eq('src/version.c', fnamemodify(filename, ':r'))
     eq('c', fnamemodify(filename, ':r:e'))
 
-    eq_slashconvert('src/version', fnamemodify(filename, ':r:r'))
-    eq_slashconvert('src/version', fnamemodify(filename, ':r:r:r'))
+    eq('src/version', fnamemodify(filename, ':r:r'))
+    eq('src/version', fnamemodify(filename, ':r:r:r'))
   end)
 
   it('handles :h', function()
@@ -136,11 +132,11 @@ describe('fnamemodify()', function()
       eq('//server///share', fnamemodify('//server///share', ':h'))
       eq('//server/share/', fnamemodify('//server/share/foo', ':h'))
 
-      eq([[\\foo\C$]], fnamemodify([[\\foo\C$]], ':h'))
-      eq([[\\foo\C$\]], fnamemodify([[\\foo\C$\]], ':h'))
-      eq([[\\foo\C$\]], fnamemodify([[\\foo\C$\bar]], ':h'))
-      eq([[\\foo\C$\]], fnamemodify([[\\foo\C$\bar]], ':h:h'))
-      eq([[//foo\C$/]], fnamemodify([[//foo\C$/bar]], ':h'))
+      eq([[//foo/C$]], fnamemodify([[\\foo\C$]], ':h'))
+      eq([[//foo/C$/]], fnamemodify([[\\foo\C$\]], ':h'))
+      eq([[//foo/C$/]], fnamemodify([[\\foo\C$\bar]], ':h'))
+      eq([[//foo/C$/]], fnamemodify([[\\foo\C$\bar]], ':h:h'))
+      eq([[//foo/C$/]], fnamemodify([[//foo\C$/bar]], ':h'))
       -- `C$` is a share name, not a file name
       eq('', fnamemodify('//foo/C$/bar', ':h:t'))
 
@@ -165,17 +161,17 @@ describe('fnamemodify()', function()
 
   it('handles :t', function()
     eq('hello.txt', fnamemodify('hello.txt', ':t'))
-    eq_slashconvert('hello.txt', fnamemodify('path/to/hello.txt', ':t'))
+    eq('hello.txt', fnamemodify('path/to/hello.txt', ':t'))
   end)
 
   it('handles :r', function()
     eq('hello', fnamemodify('hello.txt', ':r'))
-    eq_slashconvert('path/to/hello', fnamemodify('path/to/hello.txt', ':r'))
+    eq('path/to/hello', fnamemodify('path/to/hello.txt', ':r'))
   end)
 
   it('handles :e', function()
     eq('txt', fnamemodify('hello.txt', ':e'))
-    eq_slashconvert('txt', fnamemodify('path/to/hello.txt', ':e'))
+    eq('txt', fnamemodify('path/to/hello.txt', ':e'))
   end)
 
   it('handles regex replacements', function()