Flatten GNU Make directory structure

third_party/make/concat-filename.c

@@ -0,0 +1,69 @@
+/* Construct a full filename from a directory and a relative filename.
+   Copyright (C) 2001-2004, 2006-2020 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by the
+   Free Software Foundation; either version 3 of the License, or any
+   later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <haible@clisp.cons.org>.  */
+
+#include "libc/mem/mem.h"
+#include "libc/str/str.h"
+#include "third_party/make/concat-filename.h"
+#include "third_party/make/filename.h"
+#include "third_party/make/config.h"
+/* clang-format off */
+
+/* Concatenate a directory filename, a relative filename and an optional
+   suffix.  The directory may end with the directory separator.  The second
+   argument may not start with the directory separator (it is relative).
+   Return a freshly allocated filename.  Return NULL and set errno
+   upon memory allocation failure.  */
+char *
+concatenated_filename (const char *directory, const char *filename,
+                       const char *suffix)
+{
+  char *result;
+  char *p;
+
+  if (strcmp (directory, ".") == 0)
+    {
+      /* No need to prepend the directory.  */
+      result = (char *) malloc (strlen (filename)
+                                + (suffix != NULL ? strlen (suffix) : 0)
+                                + 1);
+      if (result == NULL)
+        return NULL; /* errno is set here */
+      p = result;
+    }
+  else
+    {
+      size_t directory_len = strlen (directory);
+      int need_slash =
+        (directory_len > FILE_SYSTEM_PREFIX_LEN (directory)
+         && !ISSLASH (directory[directory_len - 1]));
+      result = (char *) malloc (directory_len + need_slash
+                                + strlen (filename)
+                                + (suffix != NULL ? strlen (suffix) : 0)
+                                + 1);
+      if (result == NULL)
+        return NULL; /* errno is set here */
+      memcpy (result, directory, directory_len);
+      p = result + directory_len;
+      if (need_slash)
+        *p++ = '/';
+    }
+  p = stpcpy (p, filename);
+  if (suffix != NULL)
+    stpcpy (p, suffix);
+  return result;
+}