libgit-sys: also export some config_set functions

In preparation for implementing a higher-level Rust API for accessing
Git configs, export some of the upstream configset API via libgitpub and
libgit-sys. Since this will be exercised as part of the higher-level API
in the next commit, no tests have been added for libgit-sys.

While we're at it, add git_configset_alloc() and git_configset_free()
functions in libgitpub so that callers can manage config_set structs on
the heap. This also allows non-C external consumers to treat config_sets
as opaque structs.

Co-authored-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/libgit-sys/public_symbol_export.c

@@ -5,11 +5,47 @@
  */
 
 #include "git-compat-util.h"
+#include "config.h"
 #include "contrib/libgit-sys/public_symbol_export.h"
 #include "version.h"
 
 #pragma GCC visibility push(default)
 
+struct libgit_config_set {
+	struct config_set cs;
+};
+
+struct libgit_config_set *libgit_configset_alloc(void)
+{
+	struct libgit_config_set *cs =
+			xmalloc(sizeof(struct libgit_config_set));
+	git_configset_init(&cs->cs);
+	return cs;
+}
+
+void libgit_configset_free(struct libgit_config_set *cs)
+{
+	git_configset_clear(&cs->cs);
+	free(cs);
+}
+
+int libgit_configset_add_file(struct libgit_config_set *cs, const char *filename)
+{
+	return git_configset_add_file(&cs->cs, filename);
+}
+
+int libgit_configset_get_int(struct libgit_config_set *cs, const char *key,
+			     int *dest)
+{
+	return git_configset_get_int(&cs->cs, key, dest);
+}
+
+int libgit_configset_get_string(struct libgit_config_set *cs, const char *key,
+				char **dest)
+{
+	return git_configset_get_string(&cs->cs, key, dest);
+}
+
 const char *libgit_user_agent(void)
 {
 	return git_user_agent();

contrib/libgit-sys/public_symbol_export.h

@@ -1,6 +1,16 @@
 #ifndef PUBLIC_SYMBOL_EXPORT_H
 #define PUBLIC_SYMBOL_EXPORT_H
 
+struct libgit_config_set *libgit_configset_alloc(void);
+
+void libgit_configset_free(struct libgit_config_set *cs);
+
+int libgit_configset_add_file(struct libgit_config_set *cs, const char *filename);
+
+int libgit_configset_get_int(struct libgit_config_set *cs, const char *key, int *dest);
+
+int libgit_configset_get_string(struct libgit_config_set *cs, const char *key, char **dest);
+
 const char *libgit_user_agent(void);
 
 const char *libgit_user_agent_sanitized(void);

contrib/libgit-sys/src/lib.rs

@@ -1,15 +1,44 @@
 #[cfg(has_std__ffi__c_char)]
-use std::ffi::c_char;
+use std::ffi::{c_char, c_int};
 
 #[cfg(not(has_std__ffi__c_char))]
 #[allow(non_camel_case_types)]
 pub type c_char = i8;
 
+#[cfg(not(has_std__ffi__c_char))]
+#[allow(non_camel_case_types)]
+pub type c_int = i32;
+
 extern crate libz_sys;
 
+#[allow(non_camel_case_types)]
+#[repr(C)]
+pub struct libgit_config_set {
+    _data: [u8; 0],
+    _marker: core::marker::PhantomData<(*mut u8, core::marker::PhantomPinned)>,
+}
+
 extern "C" {
     pub fn libgit_user_agent() -> *const c_char;
     pub fn libgit_user_agent_sanitized() -> *const c_char;
+
+    pub fn libgit_configset_alloc() -> *mut libgit_config_set;
+    pub fn libgit_configset_free(cs: *mut libgit_config_set);
+
+    pub fn libgit_configset_add_file(cs: *mut libgit_config_set, filename: *const c_char) -> c_int;
+
+    pub fn libgit_configset_get_int(
+        cs: *mut libgit_config_set,
+        key: *const c_char,
+        int: *mut c_int,
+    ) -> c_int;
+
+    pub fn libgit_configset_get_string(
+        cs: *mut libgit_config_set,
+        key: *const c_char,
+        dest: *mut *mut c_char,
+    ) -> c_int;
+
 }
 
 #[cfg(test)]