Add support for junctions on Windows

src/engine/builtins.c

@@ -1893,6 +1893,28 @@ LIST *builtin_readlink( FRAME * frame, int flags )
         cbuf[numchars] = '\0';
         return list_new( object_new( cbuf ) );
     }
+    else if( okay && buf.reparse.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT )
+    {
+        int index = buf.reparse.MountPointReparseBuffer.SubstituteNameOffset / 2;
+        int length = buf.reparse.MountPointReparseBuffer.SubstituteNameLength / 2;
+        char cbuf[MAX_PATH + 1];
+        const char * result;
+        int numchars = WideCharToMultiByte( CP_ACP, 0, buf.reparse.MountPointReparseBuffer.PathBuffer + index, length, cbuf, sizeof(cbuf), NULL, NULL );
+        if( numchars >= sizeof(cbuf) )
+        {
+            return 0;
+        }
+        cbuf[numchars] = '\0';
+        /* strip off the leading "\??\" */
+        result = cbuf;
+        if ( cbuf[ 0 ] == '\\' && cbuf[ 1 ] == '?' &&
+            cbuf[ 2 ] == '?' && cbuf[ 3 ] == '\\' &&
+            cbuf[ 4 ] != '\0' && cbuf[ 5 ] == ':' )
+        {
+            result += 4;
+        }
+        return list_new( object_new( result ) );
+    }
     return 0;
 #else
     char static_buf[256];

src/tools/link.jam

@@ -60,6 +60,45 @@ rule can-symlink ( project : ps )
     }
 }
 
+if [ os.name ] = NT
+{
+
+# Test for Windows junctions (mklink /J)
+rule can-junction ( project : ps )
+{
+    if ! $(.can-junction)
+    {
+        local root-project = [ get-root-project $(project) ] ;
+
+        local source-target = [ new file-target test-junction-source : :
+            $(project) : [ new action : common.mkdir ] ] ;
+        local target = [ new file-target test-junction : :
+            $(project) : [ new action $(source-target) : link.junction ] ] ;
+
+        if [ configure.try-build $(target) : $(ps) : "junctions supported" ]
+        {
+            .can-junction = true ;
+        }       
+        else
+        {
+            .can-junction = false ;
+        }
+    }
+    if $(.can-junction) = true
+    {
+        return true ;
+    }
+}
+
+}
+else
+{
+
+rule can-junction ( project : ps )
+{
+}
+
+}
 
 rule can-hardlink ( project : ps )
 {
@@ -149,8 +188,13 @@ class symlink-target-class : basic-target
         local files = [ path.glob-tree $(location) : * ] ;
         local targets ;
 
-        link.can-symlink $(self.project) : $(property-set) ;
-        link.can-hardlink $(self.project) : $(property-set) ;
+        # If we have symlinks, don't bother checking
+        # for hardlinks and junctions.
+        if ! [ link.can-symlink $(self.project) : $(property-set) ]
+        {
+            link.can-junction $(self.project) : $(property-set) ;
+            link.can-hardlink $(self.project) : $(property-set) ;
+        }
 
         if [ $(property-set).get <location> ]
         {
@@ -216,7 +260,18 @@ rule do-link
     }
     if [ os.name ] = NT
     {
-        MKLINK_OR_DIR on $(target) = mklink /D \"$(target)\" \"$(relative)\" ;
+        if $(.can-symlink) = true
+        {
+            MKLINK_OR_DIR on $(target) = mklink /D \"$(target)\" \"$(relative)\" ;
+        }
+        else
+        {
+            # This function should only be called
+            # if either symlinks or junctions are supported.
+            # To get here $(.can-junction) must be true.
+            mklink-opt = /J ;
+            MKLINK_OR_DIR on $(target) = mklink /J \"$(target)\" \"$(source)\" ;
+        }
     }
     else
     {
@@ -329,7 +384,7 @@ rule link-recursively ( target : source : no-recurse ? )
             split = true ;
         }
     }
-    else if $(.can-symlink) = false
+    else if $(.can-symlink) = false && $(.can-junction) = false
     {
         if [ READLINK [ path.native $(target) ] ]
         {
@@ -384,6 +439,12 @@ rule mklink
 if [ os.name ] = NT
 {
 
+actions junction
+{
+    if exist "$(<)" del "$(<)"
+    mklink /J "$(<)" "$(>)"
+}
+
 actions mklink
 {
     if exist "$(<)" del "$(<)"