refactor(path): more slash normalization #39426

Problem:
1. `vim_getenv` is followed by `TO_SLASH` when getting
path-related variables.
2. cmd exits when launched with forward slash.

Solution:
1. try calling `TO_SLASH` in `vim_getenv`.
2. pass fullpath via `lpApplicationName`, only include `cmd.exe`
in cmdline.

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

src/nvim/os/env.c

@@ -618,7 +618,6 @@ size_t expand_env_esc(const char *restrict srcp, char *restrict dst, int dstlen,
 #endif
         *var = NUL;
         var = vim_getenv(dst);
-        TO_SLASH(var);
         mustfree = true;
 #ifdef UNIX
       }
@@ -872,6 +871,18 @@ char *vim_getenv(const char *name)
 #endif
 
   char *kos_env_path = os_getenv(name);
+#ifdef BACKSLASH_IN_FILENAME
+  if (striequal(name, "VIMRUNTIME")
+      || striequal(name, "PATH")
+      || striequal(name, "CDPATH")
+      || striequal(name, "TMPDIR")
+      || striequal(name, "TMP")
+      || striequal(name, "TEMP")
+      || striequal(name, "VIM")
+      || striequal(name, "MYVIMRC")) {
+    TO_SLASH(kos_env_path);
+  }
+#endif
   if (kos_env_path != NULL) {
     return kos_env_path;
   }

src/nvim/os/pty_proc_win.c

@@ -8,6 +8,7 @@
 #include "nvim/log.h"
 #include "nvim/mbyte.h"
 #include "nvim/memory.h"
+#include "nvim/os/fs.h"
 #include "nvim/os/os.h"
 #include "nvim/os/pty_conpty_win.h"
 #include "nvim/os/pty_proc_win.h"
@@ -61,6 +62,7 @@ int pty_proc_spawn(PtyProc *ptyproc)
   HANDLE proc_handle = NULL;
   uv_connect_t *in_req = NULL;
   uv_connect_t *out_req = NULL;
+  wchar_t *file = NULL;
   wchar_t *cmd_line = NULL;
   wchar_t *cwd = NULL;
   wchar_t *env = NULL;
@@ -99,8 +101,28 @@ int pty_proc_spawn(PtyProc *ptyproc)
     }
   }
 
-  status = build_cmd_line(proc->argv, &cmd_line,
-                          os_shell_is_cmdexe(proc->argv[0]));
+  // cmd.exe can’t recognize forward slash in argv[0] during
+  // initialization, so we keep only cmd.exe in the cmd_line
+  // and pass fullpath via lpApplicationName to avoid hijacking.
+  // See https://www.microsoft.com/en-us/msrc/blog/2014/04/ms14-019-fixing-a-binary-hijacking-via-cmd-or-bat-file
+  bool is_cmdexe = os_shell_is_cmdexe(proc->argv[0]);
+  if (is_cmdexe) {
+    char *path = NULL;
+    // TODO(ntdiary): Could put the search logic in one place.
+    // See https://github.com/neovim/neovim/issues/36818#issuecomment-3977147445
+    if (!os_can_exe(proc->argv[0], &path, true)) {
+      status = UV_ENOENT;
+      emsg = "executable not found";
+      goto cleanup;
+    }
+    status = utf8_to_utf16(path, -1, &file);
+    if (status != 0) {
+      emsg = "utf8_to_utf16(proc->argv[0]) failed";
+      goto cleanup;
+    }
+    xfree(path);
+  }
+  status = build_cmd_line(proc->argv, &cmd_line, is_cmdexe);
   if (status != 0) {
     emsg = "build_cmd_line failed";
     goto cleanup;
@@ -117,7 +139,7 @@ int pty_proc_spawn(PtyProc *ptyproc)
 
   if (!os_conpty_spawn(conpty_object,
                        &proc_handle,
-                       NULL,
+                       file,
                        cmd_line,
                        cwd,
                        env)) {
@@ -163,6 +185,7 @@ cleanup:
   }
   xfree(in_req);
   xfree(out_req);
+  xfree(file);
   xfree(cmd_line);
   xfree(env);
   xfree(cwd);
@@ -261,10 +284,7 @@ static int build_cmd_line(char **argv, wchar_t **cmd_line, bool is_cmdexe)
     ArgNode *arg_node = xmalloc(sizeof(*arg_node));
     arg_node->arg = xmalloc(buf_len);
     if (is_cmdexe) {
-      xstrlcpy(arg_node->arg, *argv, buf_len);
-      if (argc == 0) {
-        TO_BACKSLASH(arg_node->arg);
-      }
+      xstrlcpy(arg_node->arg, argc == 0 ? "cmd.exe" : *argv, buf_len);
     } else {
       quote_cmd_arg(arg_node->arg, buf_len, *argv);
     }

src/nvim/runtime.c

@@ -1847,8 +1847,7 @@ char *runtimepath_default(bool clean_arg)
   char *const libdir = get_lib_dir();
   char *const data_dirs = stdpaths_get_xdg_var(kXDGDataDirs);
   char *const config_dirs = stdpaths_get_xdg_var(kXDGConfigDirs);
-  char *vimruntime = vim_getenv("VIMRUNTIME");
-  TO_SLASH(vimruntime);
+  char *const vimruntime = vim_getenv("VIMRUNTIME");
 #define SITE_SIZE (sizeof("site") - 1)
 #define AFTER_SIZE (sizeof("after") - 1)
   size_t data_len = 0;

test/functional/vimscript/environ_spec.lua

@@ -35,7 +35,7 @@ describe('vim.fn.environ()', function()
         local env = vim.fn.environ()
         assert(vim.tbl_count(env) > 10, 'environ() should have some env vars!')
         for k, v in pairs(env) do
-          if v ~= '' and vim.fn.getenv(k) ~= v then
+          if v ~= '' and vim.fn.getenv(k) ~= v and vim.fn.getenv(k) ~= v:gsub('\\', '/') then
             error(('environ()[%q] = %q, but vim.fn.getenv(%q) = %q'):format(k, v, k, vim.fn.getenv(k)))
           end
         end