os_resolve_shortcut: initial port from Vim source

src/nvim/buffer.c

@@ -4030,8 +4030,8 @@ void fname_expand(buf_T *buf, char_u **ffname, char_u **sfname)
   if (!buf->b_p_bin) {
     char_u  *rfname;
 
-    /* If the file name is a shortcut file, use the file it links to. */
+    // If the file name is a shortcut file, use the file it links to.
-    rfname = mch_resolve_shortcut(*ffname);
+    rfname = os_resolve_shortcut(*ffname);
     if (rfname != NULL) {
       xfree(*ffname);
       *ffname = rfname;

src/nvim/eval.c

@@ -13592,11 +13592,12 @@ static void f_resolve(typval_T *argvars, typval_T *rettv)
   {
     char_u  *v = NULL;
 
-    v = mch_resolve_shortcut(p);
+    v = os_resolve_shortcut(p);
-    if (v != NULL)
+    if (v != NULL) {
       rettv->vval.v_string = v;
-    else
+    } else {
       rettv->vval.v_string = vim_strsave(p);
+    }
   }
 #else
 # ifdef HAVE_READLINK

src/nvim/os/fs.c

@@ -929,3 +929,133 @@ bool os_fileid_equal_fileinfo(const FileID *file_id,
          && file_id->device_id == file_info->stat.st_dev;
 }
 
+#ifdef WIN32
+# include <shlobj.h>
+/// When "fname" is the name of a shortcut (*.lnk) resolve the file it points
+/// to and return that name in allocated memory.
+/// Otherwise NULL is returned.
+char_u * os_resolve_shortcut(char_u *fname)
+{
+  HRESULT hr;
+  IShellLink *psl = NULL;
+  IPersistFile *ppf = NULL;
+  OLECHAR wsz[MAX_PATH];
+  WIN32_FIND_DATA ffd;     // we get those free of charge
+  CHAR buf[MAX_PATH];      // could have simply reused 'wsz'...
+  char_u *rfname = NULL;
+  int len;
+  IShellLinkW		*pslw = NULL;
+  WIN32_FIND_DATAW	ffdw;  // we get those free of charge
+
+  // Check if the file name ends in ".lnk". Avoid calling CoCreateInstance(),
+  // it's quite slow.
+  if (fname == NULL) {
+    return rfname;
+  }
+  len = (int)STRLEN(fname);
+  if (len <= 4 || STRNICMP(fname + len - 4, ".lnk", 4) != 0) {
+    return rfname;
+  }
+
+  CoInitialize(NULL);
+
+# ifdef FEAT_MBYTE
+  if (enc_codepage >= 0 && (int)GetACP() != enc_codepage) {
+    // create a link manager object and request its interface
+    hr = CoCreateInstance(
+        &CLSID_ShellLink, NULL, CLSCTX_INPROC_SERVER,
+        &IID_IShellLinkW, (void**)&pslw);
+    if (hr == S_OK)
+    {
+      WCHAR	*p = enc_to_utf16(fname, NULL);
+
+      if (p != NULL) {
+        // Get a pointer to the IPersistFile interface.
+        hr = pslw->lpVtbl->QueryInterface(
+            pslw, &IID_IPersistFile, (void**)&ppf);
+        if (hr != S_OK)
+          goto shortcut_errorw;
+
+        // "load" the name and resolve the link
+        hr = ppf->lpVtbl->Load(ppf, p, STGM_READ);
+        if (hr != S_OK) {
+          goto shortcut_errorw;
+        }
+
+#  if 0  // This makes Vim wait a long time if the target does not exist.
+        hr = pslw->lpVtbl->Resolve(pslw, NULL, SLR_NO_UI);
+        if (hr != S_OK) {
+          goto shortcut_errorw;
+        }
+#  endif
+
+        // Get the path to the link target.
+        ZeroMemory(wsz, MAX_PATH * sizeof(WCHAR));
+        hr = pslw->lpVtbl->GetPath(pslw, wsz, MAX_PATH, &ffdw, 0);
+        if (hr == S_OK && wsz[0] != NUL) {
+          rfname = utf16_to_enc(wsz, NULL);
+        }
+
+shortcut_errorw:
+        xfree(p);
+        goto shortcut_end;
+      }
+    }
+    /* Retry with non-wide function (for Windows 98). */
+  }
+# endif
+
+  // create a link manager object and request its interface
+  hr = CoCreateInstance(&CLSID_ShellLink, NULL, CLSCTX_INPROC_SERVER,
+                        &IID_IShellLink, (void**)&psl);
+  if (hr != S_OK) {
+    goto shortcut_end;
+  }
+
+  // Get a pointer to the IPersistFile interface.
+  hr = psl->lpVtbl->QueryInterface(psl, &IID_IPersistFile, (void**)&ppf);
+  if (hr != S_OK) {
+    goto shortcut_end;
+  }
+
+  // full path string must be in Unicode.
+  MultiByteToWideChar(CP_ACP, 0, (LPCSTR)fname, -1, wsz, MAX_PATH);
+
+  // "load" the name and resolve the link
+  hr = ppf->lpVtbl->Load(ppf, wsz, STGM_READ);
+  if (hr != S_OK) {
+    goto shortcut_end;
+  }
+
+# if 0  // This makes Vim wait a long time if the target doesn't exist.
+  hr = psl->lpVtbl->Resolve(psl, NULL, SLR_NO_UI);
+  if (hr != S_OK) {
+    goto shortcut_end;
+  }
+# endif
+
+  // Get the path to the link target.
+  ZeroMemory(buf, MAX_PATH);
+  hr = psl->lpVtbl->GetPath(psl, buf, MAX_PATH, &ffd, 0);
+  if (hr == S_OK && buf[0] != NUL) {
+    rfname = vim_strsave((char_u *)buf);
+  }
+
+shortcut_end:
+  // Release all interface pointers (both belong to the same object)
+  if (ppf != NULL) {
+    ppf->lpVtbl->Release(ppf);
+  }
+  if (psl != NULL) {
+    psl->lpVtbl->Release(psl);
+  }
+# ifdef FEAT_MBYTE
+  if (pslw != NULL) {
+    pslw->lpVtbl->Release(pslw);
+  }
+# endif
+
+  CoUninitialize();
+  return rfname;
+}
+#endif