git-save: improve commit authorship data

We used to always just commit as "subsurface@hohndel.org" because
libgit-19 doesn't have the interfaces to do user name lookup.  This does
better if you have libgit-20, using "git_signature_default()" to get the
actual user that does the saving.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

dive.h

@@ -714,6 +714,12 @@ extern const char *saved_git_id;
 extern void clear_git_id(void);
 extern void set_git_id(const struct git_oid *);
 
+struct user_info {
+	const char *name;
+	const char *email;
+};
+
+extern void subsurface_user_info(struct user_info *);
 extern int subsurface_rename(const char *path, const char *newpath);
 extern int subsurface_open(const char *path, int oflags, mode_t mode);
 extern FILE *subsurface_fopen(const char *path, const char *mode);

linux.c

@@ -2,16 +2,39 @@
 /* implements Linux specific functions */
 #include "dive.h"
 #include "display.h"
+#include "membuffer.h"
 #include <string.h>
 #include <sys/types.h>
 #include <dirent.h>
 #include <fnmatch.h>
 #include <stdio.h>
 #include <fcntl.h>
+#include <unistd.h>
+#include <pwd.h>
 
 const char system_divelist_default_font[] = "Sans";
 const int system_divelist_default_font_size = 8;
 
+void subsurface_user_info(struct user_info *user)
+{
+	struct passwd *pwd = getpwuid(getuid());
+	const char *username = getenv("USER");
+
+	if (pwd) {
+		if (pwd->pw_gecos && *pwd->pw_gecos)
+			user->name = pwd->pw_gecos;
+		if (!username)
+			username = pwd->pw_name;
+	}
+	if (username && *username) {
+		char hostname[64];
+		struct membuffer mb = { 0 };
+		gethostname(hostname, sizeof(hostname));
+		put_format(&mb, "%s@%s", username, hostname);
+		user->email = mb_cstring(&mb);
+	}
+}
+
 const char *system_default_filename(void)
 {
 	const char *home, *user;

macos.c

@@ -13,6 +13,9 @@
 #include <fcntl.h>
 #include <dirent.h>
 
+void subsurface_user_info(struct user_info *info)
+{ /* Nothing, let's use libgit2-20 on MacOS */ }
+
 /* macos defines CFSTR to create a CFString object from a constant,
  * but no similar macros if a C string variable is supposed to be
  * the argument. We add this here (hardcoding the default allocator

save-git.c

@@ -815,6 +815,24 @@ static int update_git_checkout(git_repository *repo, git_object *parent, git_tre
 	return git_checkout_tree(repo, (git_object *) tree, &opts);
 }
 
+static int get_authorship(git_repository *repo, git_signature **authorp)
+{
+#if LIBGIT2_VER_MAJOR || LIBGIT2_VER_MINOR >= 20
+	return git_signature_default(authorp, repo);
+#else
+	/* Default name information, with potential OS overrides */
+	struct user_info user = {
+		.name = "Subsurface",
+		.email = "subsurace@hohndel.org"
+	};
+
+	subsurface_user_info(&user);
+
+	/* git_signature_default() is too recent */
+	return git_signature_now(authorp, user.name, user.email);
+#endif
+}
+
 static int create_new_commit(git_repository *repo, const char *branch, git_oid *tree_id)
 {
 	int ret;
@@ -853,8 +871,7 @@ static int create_new_commit(git_repository *repo, const char *branch, git_oid *
 	if (git_tree_lookup(&tree, repo, tree_id))
 		return report_error("Could not look up newly created tree");
 
-	/* git_signature_default() is too recent */
-	if (git_signature_now(&author, "Subsurface", "subsurface@hohndel.org"))
+	if (get_authorship(repo, &author))
 		return report_error("No user name configuration in git repo");
 
 	/* If the parent commit has the same tree ID, do not create a new commit */
@@ -897,6 +914,8 @@ static int create_new_commit(git_repository *repo, const char *branch, git_oid *
 		return report_error("Failed to update branch '%s'", branch);
 	set_git_id(&commit_id);
 
+	git_signature_free(author);
+
 	return 0;
 }
 

windows.c

@@ -14,6 +14,9 @@
 const char system_divelist_default_font[] = "Sans";
 const int system_divelist_default_font_size = 8;
 
+void subsurface_user(struct user_info *user)
+{ /* Encourage use of at least libgit2-0.20 */ }
+
 const char *system_default_filename(void)
 {
 	char datapath[MAX_PATH];