[PATCH 1/3] Allow debugging unsafe directories' ownership

["Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>]

From: Johannes Schindelin <johannes.schindelin@gmx.de>

When Git refuses to use an existing repository because it is owned by
someone else than the current user, it can be a bit tricky on Windows to
figure out what is going on.

Let's help with that by offering some more information via the
environment variable `GIT_TEST_DEBUG_UNSAFE_DIRECTORIES`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Documentation/config/safe.txt |  6 ++++++
 compat/mingw.c                | 21 +++++++++++++++++++++
 setup.c                       | 14 ++++++++++++--
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/Documentation/config/safe.txt b/Documentation/config/safe.txt
index 74627c5e7c6..18fac9cb7f3 100644
--- a/Documentation/config/safe.txt
+++ b/Documentation/config/safe.txt
@@ -40,3 +40,9 @@ which id the original user has.
 If that is not what you would prefer and want git to only trust
 repositories that are owned by root instead, then you can remove
 the `SUDO_UID` variable from root's environment before invoking git.
++
+Due to the permission model on Windows where ACLs are used instead of
+Unix' simpler permission model, it can be a bit tricky to figure out why
+a directory is considered unsafe. To help with this, Git will provide
+more detailed information when the environment variable
+`GIT_TEST_DEBUG_UNSAFE_DIRECTORIES` is set to `true`.
diff --git a/compat/mingw.c b/compat/mingw.c
index 38ac35913df..912444fb3ab 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -1,6 +1,7 @@
 #include "../git-compat-util.h"
 #include "win32.h"
 #include <aclapi.h>
+#include <sddl.h>
 #include <conio.h>
 #include <wchar.h>
 #include "../strbuf.h"
@@ -2676,6 +2677,26 @@ int is_path_owned_by_current_sid(const char *path)
 		    IsValidSid(current_user_sid) &&
 		    EqualSid(sid, current_user_sid))
 			result = 1;
+		else if (git_env_bool("GIT_TEST_DEBUG_UNSAFE_DIRECTORIES", 0)) {
+			LPSTR str1, str2, to_free1 = NULL, to_free2 = NULL;
+
+			if (ConvertSidToStringSidA(sid, &str1))
+				to_free1 = str1;
+			else
+				str1 = "(inconvertible)";
+
+			if (!current_user_sid)
+				str2 = "(none)";
+			else if (!IsValidSid(current_user_sid))
+				str2 = "(invalid)";
+			else if (ConvertSidToStringSidA(current_user_sid, &str2))
+				to_free2 = str2;
+			else
+				str2 = "(inconvertible)";
+			warning("'%s' is owned by:\n\t'%s'\nbut the current user is:\n\t'%s'", path, str1, str2);
+			LocalFree(to_free1);
+			LocalFree(to_free2);
+		}
 	}
 
 	/*
diff --git a/setup.c b/setup.c
index 9dcecda65b0..3ba42ffcb27 100644
--- a/setup.c
+++ b/setup.c
@@ -1353,13 +1353,23 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	case GIT_DIR_INVALID_OWNERSHIP:
 		if (!nongit_ok) {
 			struct strbuf quoted = STRBUF_INIT;
+			struct strbuf hint = STRBUF_INIT;
+
+#ifdef __MINGW32__
+			if (!git_env_bool("GIT_TEST_DEBUG_UNSAFE_DIRECTORIES", 0))
+				strbuf_addstr(&hint,
+					      _("\n\nSet the environment variable "
+						"GIT_TEST_DEBUG_UNSAFE_DIRECTORIES=true "
+						"and run\n"
+						"again for more information."));
+#endif
 
 			sq_quote_buf_pretty(&quoted, dir.buf);
 			die(_("detected dubious ownership in repository at '%s'\n"
 			      "To add an exception for this directory, call:\n"
 			      "\n"
-			      "\tgit config --global --add safe.directory %s"),
-			    dir.buf, quoted.buf);
+			      "\tgit config --global --add safe.directory %s%s"),
+			    dir.buf, quoted.buf, hint.buf);
 		}
 		*nongit_ok = 1;
 		break;
-- 
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