Merge 'virtual-file-system-support'

Add virtual file system settings and hook proc.  On index load,
clear/set the skip worktree bits based on the virtual file system data.
Use virtual file system data to update skip-worktree bit in
unpack-trees. Use virtual file system data to exclude files and folders
not explicitly requested.

Signed-off-by: Ben Peart <Ben.Peart@microsoft.com>

Documentation/config.txt

@@ -430,6 +430,14 @@ core.fsmonitor::
 	avoiding unnecessary processing of files that have not changed.
 	See the "fsmonitor-watchman" section of linkgit:githooks[5].
 
+core.virtualFilesystem::
+	If set, the value of this variable is used as a command which
+	will identify all files and directories that are present in
+	the working directory.  Git will only track and update files
+	listed in the virtual file system.  Using the virtual file system
+	will supersede the sparse-checkout settings which will be ignored.
+	See the "virtual file system" section of linkgit:githooks[6].
+
 core.trustctime::
 	If false, the ctime differences between the index and the
 	working tree are ignored; useful when the inode change time
@@ -928,10 +936,6 @@ core.gvfs::
 	GVFS_SKIP_SHA_ON_INDEX_READ::
 		Bit value 1
 		Disables the calculation and validation of the sha when reading the index
-	GVFS_SPARSE_HASHMAP::
-		Bit value 2
-		Changes sparse-checkout to use a hashmap to speed up lookups.
-		Only works with pathnames and directories (no wildcards, negatives, tokens, etc).
 	GVFS_MISSING_OK::
 		Bit value 4
 		Normally git write-tree ensures that the objects referenced by the
@@ -983,12 +987,6 @@ core.gvfs::
 		   happened.
 		This drops the merge time from ~1 hour to ~5 minutes and the unmerged
 		entries goes down from ~40,000 to 1.
-	GVFS_ALWAYS_EXCLUDE_HASHMAP::
-		Bit value 512
-		Changes always_exclude to use a hashmap to speed up lookups.
-		Only works with exact matches and same-folder wildcards (pa/th/*)
-		and supports negatives.  Behavior depends on GVFS's usage pattern
-		and is unlikely to work correctly otherwise.
 --
 
 core.midx::

Documentation/githooks.txt

@@ -484,6 +484,26 @@ The exit status determines whether git will use the data from the
 hook to limit its search.  On error, it will fall back to verifying
 all files and folders.
 
+virtualFilesystem
+~~~~~~~~~~~~~~~~~~
+
+"Virtual File System" allows populating the working directory sparsely.
+The projection data is typically automatically generated by an external
+process.  Git will limit what files it checks for changes as well as which
+directories are checked for untracked files based on the path names given.
+Git will also only update those files listed in the projection.
+
+The hook is invoked when the configuration option core.virtualFilesystem
+is set.  It takes one argument, a version (currently 1).
+
+The hook should output to stdout the list of all files in the working
+directory that git should track.  The paths are relative to the root
+of the working directory and are separated by a single NUL.  Full paths
+('dir1/a.txt') as well as directories are supported (ie 'dir1/').
+
+The exit status determines whether git will use the data from the
+hook.  On error, git will abort the command with an error message.
+
 GIT
 ---
 Part of the linkgit:git[1] suite

Makefile

@@ -927,6 +927,7 @@ LIB_OBJS += utf8.o
 LIB_OBJS += varint.o
 LIB_OBJS += version.o
 LIB_OBJS += versioncmp.o
+LIB_OBJS += virtualfilesystem.o
 LIB_OBJS += walker.o
 LIB_OBJS += wildmatch.o
 LIB_OBJS += worktree.o

cache.h

@@ -829,6 +829,7 @@ extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_commit_graph;
 extern int core_apply_sparse_checkout;
+extern const char *core_virtualfilesystem;
 extern int core_gvfs;
 extern int core_midx;
 extern int precomposed_unicode;

config.c

@@ -1243,7 +1243,11 @@ static int git_default_core_config(const char *var, const char *value, void *cb)
 	}
 
 	if (!strcmp(var, "core.sparsecheckout")) {
-		core_apply_sparse_checkout = git_config_bool(var, value);
+		/* virtual file system relies on the sparse checkout logic so force it on */
+		if (core_virtualfilesystem)
+			core_apply_sparse_checkout = 1;
+		else
+			core_apply_sparse_checkout = git_config_bool(var, value);
 		return 0;
 	}
 
@@ -2210,6 +2214,23 @@ int git_config_get_fsmonitor(void)
 	return 0;
 }
 
+int git_config_get_virtualfilesystem(void)
+{
+	if (git_config_get_pathname("core.virtualfilesystem", &core_virtualfilesystem))
+		core_virtualfilesystem = getenv("GIT_VIRTUALFILESYSTEM_TEST");
+
+	if (core_virtualfilesystem && !*core_virtualfilesystem)
+		core_virtualfilesystem = NULL;
+
+	/* virtual file system relies on the sparse checkout logic so force it on */
+	if (core_virtualfilesystem) {
+		core_apply_sparse_checkout = 1;
+		return 1;
+	}
+
+	return 0;
+}
+
 NORETURN
 void git_die_config_linenr(const char *key, const char *filename, int linenr)
 {

config.h

@@ -214,6 +214,7 @@ extern int git_config_get_untracked_cache(void);
 extern int git_config_get_split_index(void);
 extern int git_config_get_max_percent_split_change(void);
 extern int git_config_get_fsmonitor(void);
+extern int git_config_get_virtualfilesystem(void);
 
 /* This dies if the configured or default date is in the future */
 extern int git_config_get_expiry(const char *key, const char **output);