Introduce GIT_CALLBACK macro to enforce cdecl

Since we now always build the library with cdecl calling conventions,
our callbacks should be decorated as such so that users will not be able
to provide callbacks defined with other calling conventions.

The `GIT_CALLBACK` macro will inject the `__cdecl` attribute as
appropriate.

Author: ethomson

include/git2/apply.h

@@ -33,7 +33,7 @@ GIT_BEGIN_DECL
  * @param delta The delta to be applied
  * @param payload User-specified payload
  */
-typedef int (*git_apply_delta_cb)(
+typedef int GIT_CALLBACK(git_apply_delta_cb)(
 	const git_diff_delta *delta,
 	void *payload);
 
@@ -49,7 +49,7 @@ typedef int (*git_apply_delta_cb)(
  * @param hunk The hunk to be applied
  * @param payload User-specified payload
  */
-typedef int (*git_apply_hunk_cb)(
+typedef int GIT_CALLBACK(git_apply_hunk_cb)(
 	const git_diff_hunk *hunk,
 	void *payload);
 

include/git2/attr.h

@@ -202,7 +202,7 @@ GIT_EXTERN(int) git_attr_get_many(
  * @return 0 to continue looping, non-zero to stop. This value will be returned
  *         from git_attr_foreach.
  */
-typedef int (*git_attr_foreach_cb)(const char *name, const char *value, void *payload);
+typedef int GIT_CALLBACK(git_attr_foreach_cb)(const char *name, const char *value, void *payload);
 
 /**
  * Loop over all the git attributes for a path.

include/git2/checkout.h

@@ -220,7 +220,7 @@ typedef struct {
 } git_checkout_perfdata;
 
 /** Checkout notification callback function */
-typedef int (*git_checkout_notify_cb)(
+typedef int GIT_CALLBACK(git_checkout_notify_cb)(
 	git_checkout_notify_t why,
 	const char *path,
 	const git_diff_file *baseline,
@@ -229,14 +229,14 @@ typedef int (*git_checkout_notify_cb)(
 	void *payload);
 
 /** Checkout progress notification function */
-typedef void (*git_checkout_progress_cb)(
+typedef void GIT_CALLBACK(git_checkout_progress_cb)(
 	const char *path,
 	size_t completed_steps,
 	size_t total_steps,
 	void *payload);
 
 /** Checkout perfdata notification function */
-typedef void (*git_checkout_perfdata_cb)(
+typedef void GIT_CALLBACK(git_checkout_perfdata_cb)(
 	const git_checkout_perfdata *perfdata,
 	void *payload);
 

include/git2/clone.h

@@ -66,7 +66,7 @@ typedef enum {
  * @param payload an opaque payload
  * @return 0, GIT_EINVALIDSPEC, GIT_EEXISTS or an error code
  */
-typedef int (*git_remote_create_cb)(
+typedef int GIT_CALLBACK(git_remote_create_cb)(
 	git_remote **out,
 	git_repository *repo,
 	const char *name,
@@ -87,7 +87,7 @@ typedef int (*git_remote_create_cb)(
  * @param payload payload specified by the options
  * @return 0, or a negative value to indicate error
  */
-typedef int (*git_repository_create_cb)(
+typedef int GIT_CALLBACK(git_repository_create_cb)(
 	git_repository **out,
 	const char *path,
 	int bare,

include/git2/common.h

@@ -48,6 +48,13 @@ typedef size_t size_t;
 # define GIT_EXTERN(type) extern type
 #endif
 
+/** Declare a callback function for application use. */
+#if defined(_MSC_VER)
+# define GIT_CALLBACK(name) (__cdecl *name)
+#else
+# define GIT_CALLBACK(name) (*name)
+#endif
+
 /** Declare a function as deprecated. */
 #if defined(__GNUC__)
 # define GIT_DEPRECATED(func) \

include/git2/config.h

@@ -66,7 +66,7 @@ typedef struct git_config_entry {
 	const char *value; /**< String value of the entry */
 	unsigned int include_depth; /**< Depth of includes where this variable was found */
 	git_config_level_t level; /**< Which config file this was found in */
-	void (*free)(struct git_config_entry *entry); /**< Free function for this entry */
+	void GIT_CALLBACK(free)(struct git_config_entry *entry); /**< Free function for this entry */
 	void *payload; /**< Opaque value for the free function. Do not read or write */
 } git_config_entry;
 
@@ -81,7 +81,7 @@ GIT_EXTERN(void) git_config_entry_free(git_config_entry *);
  * @param entry the entry currently being enumerated
  * @param payload a user-specified pointer
  */
-typedef int  (*git_config_foreach_cb)(const git_config_entry *entry, void *payload);
+typedef int GIT_CALLBACK(git_config_foreach_cb)(const git_config_entry *entry, void *payload);
 
 /**
  * An opaque structure for a configuration iterator

include/git2/diff.h

@@ -328,7 +328,7 @@ typedef struct {
  * - returns 0, the delta is inserted into the diff, and the diff process
  *		continues.
  */
-typedef int (*git_diff_notify_cb)(
+typedef int GIT_CALLBACK(git_diff_notify_cb)(
 	const git_diff *diff_so_far,
 	const git_diff_delta *delta_to_add,
 	const char *matched_pathspec,
@@ -344,7 +344,7 @@ typedef int (*git_diff_notify_cb)(
  * @param new_path The path to the new file or NULL.
  * @return Non-zero to abort the diff.
  */
-typedef int (*git_diff_progress_cb)(
+typedef int GIT_CALLBACK(git_diff_progress_cb)(
 	const git_diff *diff_so_far,
 	const char *old_path,
 	const char *new_path,
@@ -462,7 +462,7 @@ GIT_EXTERN(int) git_diff_init_options(
  * @param progress Goes from 0 to 1 over the diff
  * @param payload User-specified pointer from foreach function
  */
-typedef int (*git_diff_file_cb)(
+typedef int GIT_CALLBACK(git_diff_file_cb)(
 	const git_diff_delta *delta,
 	float progress,
 	void *payload);
@@ -528,7 +528,7 @@ typedef struct {
  * When iterating over a diff, callback that will be made for
  * binary content within the diff.
  */
-typedef int(*git_diff_binary_cb)(
+typedef int GIT_CALLBACK(git_diff_binary_cb)(
 	const git_diff_delta *delta,
 	const git_diff_binary *binary,
 	void *payload);
@@ -554,7 +554,7 @@ typedef struct {
 /**
  * When iterating over a diff, callback that will be made per hunk.
  */
-typedef int (*git_diff_hunk_cb)(
+typedef int GIT_CALLBACK(git_diff_hunk_cb)(
 	const git_diff_delta *delta,
 	const git_diff_hunk *hunk,
 	void *payload);
@@ -615,7 +615,7 @@ typedef struct {
  * of text.  This uses some extra GIT_DIFF_LINE_... constants for output
  * of lines of file and hunk headers.
  */
-typedef int (*git_diff_line_cb)(
+typedef int GIT_CALLBACK(git_diff_line_cb)(
 	const git_diff_delta *delta, /**< delta that contains this data */
 	const git_diff_hunk *hunk,   /**< hunk containing this data */
 	const git_diff_line *line,   /**< line data */
@@ -699,14 +699,14 @@ typedef enum {
  * Pluggable similarity metric
  */
 typedef struct {
-	int (*file_signature)(
+	int GIT_CALLBACK(file_signature)(
 		void **out, const git_diff_file *file,
 		const char *fullpath, void *payload);
-	int (*buffer_signature)(
+	int GIT_CALLBACK(buffer_signature)(
 		void **out, const git_diff_file *file,
 		const char *buf, size_t buflen, void *payload);
-	void (*free_signature)(void *sig, void *payload);
-	int (*similarity)(int *score, void *siga, void *sigb, void *payload);
+	void GIT_CALLBACK(free_signature)(void *sig, void *payload);
+	int GIT_CALLBACK(similarity)(int *score, void *siga, void *sigb, void *payload);
 	void *payload;
 } git_diff_similarity_metric;
 

include/git2/index.h

@@ -132,7 +132,7 @@ typedef enum {
 
 
 /** Callback for APIs that add/remove/update files matching pathspec */
-typedef int (*git_index_matched_path_cb)(
+typedef int GIT_CALLBACK(git_index_matched_path_cb)(
 	const char *path, const char *matched_pathspec, void *payload);
 
 /** Flags for APIs that add files matching pathspec */

include/git2/net.h

@@ -52,7 +52,7 @@ struct git_remote_head {
 /**
  * Callback for listing the remote heads
  */
-typedef int (*git_headlist_cb)(git_remote_head *rhead, void *payload);
+typedef int GIT_CALLBACK(git_headlist_cb)(git_remote_head *rhead, void *payload);
 
 /** @} */
 GIT_END_DECL

include/git2/notes.h

@@ -26,7 +26,7 @@ GIT_BEGIN_DECL
  * - annotated_object_id: Oid of the git object being annotated
  * - payload: Payload data passed to `git_note_foreach`
  */
-typedef int (*git_note_foreach_cb)(
+typedef int GIT_CALLBACK(git_note_foreach_cb)(
 	const git_oid *blob_id, const git_oid *annotated_object_id, void *payload);
 
 /**