From afd8d80e47348105616c8c411029c4ec0361d0ba Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 11 Jul 2016 20:14:00 -0700
Subject: Implement drive-relative paths and per-drive working dir.

* winsup/cygwin/path.cc (normalize_win32_path): When
a drive-relative path is normalized, look up the remembered
working directory of that drive in the environment.
A drive-relative path is, for example, "C:file.txt".
Or just "C:", with no component.  If there is no path
for the drive in the environment, then the root directory
is used, and the "C:" part thus becomes "C:\", causing
the path to refer to "C:\file.txt". Otherwise the path is
inserted, with a backslash, like "C:\users\bob\file.txt".
The Windows convention for storing these per-drive paths
in the environment is to use environment variables based
on drive letters. For instance the path for the C drive is
stored in the environment variable "!C:" (bang, letter, colon).
The path includes the C:\ prefix.
(cwdstuff::override_win32_cwd): Add the behavior of associating
the current working directory with its drive (if it is a
current working directory based on a drive). For instance
if the overriding cwd is "C:\Users", then the "C:\Users"
path is stored into the "!C:" environment variable.
---
 winsup/cygwin/path.cc | 44 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 42 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index 6fb228b6d..98e6d5744 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -1408,8 +1408,34 @@ normalize_win32_path (const char *src, char *dst, char *&tail)
   if (tail == dst)
     {
       if (isdrive (src))
-	/* Always convert drive letter to uppercase for case sensitivity. */
-	*tail++ = cyg_toupper (*src++);
+        {
+	  /* Drive followed by separator is an absolute path */
+	  if (isdirsep (src[2]))
+	    /* Always convert drive letter to uppercase for case sensitivity. */
+	    *tail++ = cyg_toupper (*src++);
+	  else
+	    {
+	      /* Drive-relative path: get drive path from environment. */
+	      char env[] = { '!', cyg_toupper (*src), ':', 0 };
+	      const char *drvpath = getenv(env);
+
+	      if (drvpath)
+		{
+		  size_t len = strlcpy(tail, drvpath, NT_MAX_PATH);
+
+		  if (len >= NT_MAX_PATH - 1)
+		    return ENAMETOOLONG;
+
+		  tail += len;
+		  *tail++ = '\\';
+		  src += 2;
+		}
+	      else
+		{
+		  *tail++ = cyg_toupper (*src++);
+		}
+	    }
+	}
       else
 	{
 	  if (beg_src_slash)
@@ -4435,6 +4461,20 @@ cwdstuff::override_win32_cwd (bool init, ULONG old_dismount_count)
 	 from the parent process.  We always have to close it here. */
       NtClose (h);
     }
+
+  /* Simulate the SetCurrentDirectory effect of associating a drive
+     with its own current directory. This behavior dating all the way
+     back to MS-DOS is done in Windows with special environment
+     variables. */
+  if (iswdrive (win32.Buffer)) {
+    tmp_pathbuf tp;
+    char env[] = { '!', (char) win32.Buffer[0], ':', 0 };
+    char *cwdcopy = tp.c_get ();
+
+    sys_wcstombs (cwdcopy, NT_MAX_PATH, win32.Buffer,
+		  win32.Length / sizeof (WCHAR));
+    setenv(env, cwdcopy, 1);
+  }
 }
 
 /* Initialize cygcwd 'muto' for serializing access to cwd info. */
-- 
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