utf8_to_utf16: align with libuv

- take a size parameter
- always NUL-terminate the result
- return libuv error code
- handle error in caller only (avoid redundant messages)

https://github.com/libuv/libuv/commit/53995a3825d23eacd01e2bcfa35642c4a188d32b
https://github.com/libuv/libuv/commit/4c945f49365ab4d6e1b07bf0ef2893455dc04622

4 files changed, 47 insertions, 51 deletions

diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index fae7635d34..e40beed0dd 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -1356,45 +1356,41 @@ static int utf_strnicmp(const char_u *s1, const char_u *s2, size_t n1,
 # define CP_UTF8 65001  /* magic number from winnls.h */
 #endif
 
-/// Reassigns `strw` to a new, allocated pointer to a UTF16 string.
-int utf8_to_utf16(const char *str, wchar_t **strw)
+/// Converts string from UTF-8 to UTF-16.
+///
+/// @param utf8  UTF-8 string.
+/// @param utf8len  Length of `utf8`. May be -1 if `utf8` is NUL-terminated.
+/// @param utf16[out,allocated]  NUL-terminated UTF-16 string, or NULL on error
+/// @return 0 on success, or libuv error code
+int utf8_to_utf16(const char *utf8, int utf8len, wchar_t **utf16)
   FUNC_ATTR_NONNULL_ALL
 {
-  ssize_t wchar_len = 0;
-
-  // Compute the length needed to store the converted widechar string.
-  wchar_len = MultiByteToWideChar(CP_UTF8,
-                                  0,     // dwFlags: must be 0 for utf8
-                                  str,   // lpMultiByteStr: string to convert
-                                  -1,    // -1 => process up to NUL
-                                  NULL,  // lpWideCharStr: converted string
-                                  0);    // 0  => return length, don't convert
-  if (wchar_len == 0) {
-    return GetLastError();
-  }
-
-  ssize_t buf_sz = wchar_len * sizeof(wchar_t);
-
-  if (buf_sz == 0) {
-    *strw = NULL;
-    return 0;
+  // Compute the length needed for the converted UTF-16 string.
+  int bufsize = MultiByteToWideChar(CP_UTF8,
+                                    0,     // dwFlags: must be 0 for UTF-8
+                                    utf8,  // -1: process up to NUL
+                                    utf8len,
+                                    NULL,
+                                    0);    // 0: get length, don't convert
+  if (bufsize == 0) {
+    *utf16 = NULL;
+    return uv_translate_sys_error(GetLastError());
   }
 
-  char *buf = xmalloc(buf_sz);
-  char *pos = buf;
+  // Allocate the destination buffer adding an extra byte for the terminating
+  // NULL. If `utf8len` is not -1 MultiByteToWideChar will not add it, so
+  // we do it ourselves always, just in case.
+  *utf16 = xmalloc(sizeof(wchar_t) * (bufsize + 1));
 
-  int r = MultiByteToWideChar(CP_UTF8,
-                              0,
-                              str,
-                              -1,
-                              (wchar_t *)pos,
-                              wchar_len);
-  assert(r == wchar_len);
-  if (r != wchar_len) {
-    EMSG2("MultiByteToWideChar failed: %d", r);
+  // Convert to UTF-16.
+  bufsize = MultiByteToWideChar(CP_UTF8, 0, utf8, utf8len, *utf16, bufsize);
+  if (bufsize == 0) {
+    xfree(*utf16);
+    *utf16 = NULL;
+    return uv_translate_sys_error(GetLastError());
   }
-  *strw = (wchar_t *)pos;
 
+  (*utf16)[bufsize] = L'\0';
   return 0;
 }
 
diff --git a/src/nvim/message.c b/src/nvim/message.c
index b043df17d3..6e935022ca 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -2559,10 +2559,11 @@ static int do_more_prompt(int typed_char)
 #if defined(WIN32)
 void mch_errmsg(char *str)
 {
+  assert(str != NULL);
   wchar_t *utf16str;
-  int conversion_result = utf8_to_utf16((str), &utf16str);
-  if (conversion_result != 0) {
-    EMSG2("utf8_to_utf16 failed: %d", conversion_result);
+  int r = utf8_to_utf16(str, -1, &utf16str);
+  if (r != 0) {
+    fprintf(stderr, "utf8_to_utf16 failed: %d", r);
   } else {
     fwprintf(stderr, L"%ls", utf16str);
     xfree(utf16str);
@@ -2572,10 +2573,11 @@ void mch_errmsg(char *str)
 // Give a message.  To be used when the UI is not initialized yet.
 void mch_msg(char *str)
 {
+  assert(str != NULL);
   wchar_t *utf16str;
-  int conversion_result = utf8_to_utf16((str), &utf16str);
-  if (conversion_result != 0) {
-    EMSG2("utf8_to_utf16 failed: %d", conversion_result);
+  int r = utf8_to_utf16(str, -1, &utf16str);
+  if (r != 0) {
+    fprintf(stderr, "utf8_to_utf16 failed: %d", r);
   } else {
     wprintf(L"%ls", utf16str);
     xfree(utf16str);
diff --git a/src/nvim/os/fs.c b/src/nvim/os/fs.c
index dcb3ef7c4a..615ab143b2 100644
--- a/src/nvim/os/fs.c
+++ b/src/nvim/os/fs.c
@@ -1180,12 +1180,10 @@ char *os_resolve_shortcut(const char *fname)
                         &IID_IShellLinkW, (void **)&pslw);
   if (hr == S_OK) {
     wchar_t *p;
-    const int conversion_result = utf8_to_utf16(fname, &p);
+    const int conversion_result = utf8_to_utf16(fname, len, &p);
     if (conversion_result != 0) {
       EMSG2("utf8_to_utf16 failed: %d", conversion_result);
-    }
-
-    if (p != NULL) {
+    } else if (p != NULL) {
       // Get a pointer to the IPersistFile interface.
       hr = pslw->lpVtbl->QueryInterface(
           pslw, &IID_IPersistFile, (void **)&ppf);
diff --git a/src/nvim/os/pty_process_win.c b/src/nvim/os/pty_process_win.c
index 290668bca3..ef48da953a 100644
--- a/src/nvim/os/pty_process_win.c
+++ b/src/nvim/os/pty_process_win.c
@@ -93,9 +93,9 @@ int pty_process_spawn(PtyProcess *ptyproc)
   }
 
   if (proc->cwd != NULL) {
-    status = utf8_to_utf16(proc->cwd, &cwd);
+    status = utf8_to_utf16(proc->cwd, -1, &cwd);
     if (status != 0) {
-      emsg = "Failed to convert pwd form utf8 to utf16.";
+      emsg = "utf8_to_utf16 failed";
       goto cleanup;
     }
   }
@@ -103,7 +103,7 @@ int pty_process_spawn(PtyProcess *ptyproc)
   status = build_cmd_line(proc->argv, &cmd_line,
                           os_shell_is_cmdexe(proc->argv[0]));
   if (status != 0) {
-    emsg = "Failed to convert cmd line form utf8 to utf16.";
+    emsg = "build_cmd_line failed";
     goto cleanup;
   }
 
@@ -115,7 +115,7 @@ int pty_process_spawn(PtyProcess *ptyproc)
       NULL,  // Optional environment variables
       &err);
   if (spawncfg == NULL) {
-    emsg = "Failed winpty_spawn_config_new.";
+    emsg = "winpty_spawn_config_new failed";
     goto cleanup;
   }
 
@@ -128,9 +128,9 @@ int pty_process_spawn(PtyProcess *ptyproc)
                     &err)) {
     if (win_err) {
       status = (int)win_err;
-      emsg = "Failed spawn process.";
+      emsg = "failed to spawn process";
     } else {
-      emsg = "Failed winpty_spawn.";
+      emsg = "winpty_spawn failed";
     }
     goto cleanup;
   }
@@ -160,11 +160,11 @@ int pty_process_spawn(PtyProcess *ptyproc)
 cleanup:
   if (status) {
     // In the case of an error of MultiByteToWideChar or CreateProcessW.
-    ELOG("%s error code: %d", emsg, status);
+    ELOG("%s: error code: %d", emsg, status);
     status = os_translate_sys_error(status);
   } else if (err != NULL) {
     status = (int)winpty_error_code(err);
-    ELOG("%s error code: %d", emsg, status);
+    ELOG("%s: error code: %d", emsg, status);
     status = translate_winpty_error(status);
   }
   winpty_error_free(err);
@@ -308,7 +308,7 @@ static int build_cmd_line(char **argv, wchar_t **cmd_line, bool is_cmdexe)
     }
   }
 
-  int result = utf8_to_utf16(utf8_cmd_line, cmd_line);
+  int result = utf8_to_utf16(utf8_cmd_line, -1, cmd_line);
   xfree(utf8_cmd_line);
   return result;
 }