From: Johannes Schindelin <redacted>

Over the course of Scalar's development, it became obvious that there is
a need for a command that can gather all kinds of useful information
that can help identify the most typical problems with large
worktrees/repositories.

The `diagnose` command is the culmination of this hard-won knowledge: it
gathers the installed hooks, the config, a couple statistics describing
the data shape, among other pieces of information, and then wraps
everything up in a tidy, neat `.zip` archive.

Note: originally, Scalar was implemented in C# using the .NET API, where
we had the luxury of a comprehensive standard library that includes
basic functionality such as writing a `.zip` file. In the C version, we
lack such a commodity. Rather than introducing a dependency on, say,
libzip, we slightly abuse Git's `archive` machinery: we write out a
`.zip` of the empty try, augmented by a couple files that are added via
the `--add-file*` options. We are careful trying not to modify the
current repository in any way lest the very circumstances that required
`scalar diagnose` to be run are changed by the `diagnose` run itself.

Signed-off-by: Johannes Schindelin <redacted>
---
 contrib/scalar/scalar.c          | 144 +++++++++++++++++++++++++++++++
 contrib/scalar/scalar.txt        |  12 +++
 contrib/scalar/t/t9099-scalar.sh |  14 +++
 3 files changed, 170 insertions(+)

diff --git a/contrib/scalar/scalar.c b/contrib/scalar/scalar.c
index 00dcd4b50ef..367a2c50e25 100644
--- a/contrib/scalar/scalar.c
+++ b/contrib/scalar/scalar.c

@@ -11,6 +11,7 @@
 #include "dir.h"
 #include "packfile.h"
 #include "help.h"
+#include "archive.h"
 
 /*
  * Remove the deepest subdirectory in the provided path string. Path must not

@@ -261,6 +262,47 @@ static int unregister_dir(void)
 	return res;
 }
 
+static int add_directory_to_archiver(struct strvec *archiver_args,
+					  const char *path, int recurse)
+{
+	int at_root = !*path;
+	DIR *dir = opendir(at_root ? "." : path);
+	struct dirent *e;
+	struct strbuf buf = STRBUF_INIT;
+	size_t len;
+	int res = 0;
+
+	if (!dir)
+		return error(_("could not open directory '%s'"), path);