3 files changed, 34 insertions, 16 deletions
diff --git a/source/blender/blenkernel/BKE_context.h b/source/blender/blenkernel/BKE_context.h
index f3e4a18b9bd..5c534803781 100644
--- a/source/blender/blenkernel/BKE_context.h
+++ b/source/blender/blenkernel/BKE_context.h
@@ -74,9 +74,26 @@ typedef struct bContext bContext;
 struct bContextDataResult;
 typedef struct bContextDataResult bContextDataResult;
 
-typedef int (*bContextDataCallback)(const bContext *C,
-                                    const char *member,
-                                    bContextDataResult *result);
+/* Result of context lookups.
+ * The specific values are important, and used implicitly in ctx_data_get(). Some functions also
+ * still accept/return `int` instead, to ensure that the compiler uses the correct storage size
+ * when mixing C/C++ code. */
+typedef enum eContextResult {
+  /* The context member was found, and its data is available. */
+  CTX_RESULT_OK = 1,
+
+  /* The context member was not found. */
+  CTX_RESULT_MEMBER_NOT_FOUND = 0,
+
+  /* The context member was found, but its data is not available.
+   * For example, "active_bone" is a valid context member, but has not data in Object mode. */
+  CTX_RESULT_NO_DATA = -1,
+} eContextResult;
+
+/* Function mapping a context member name to its value. */
+typedef int /*eContextResult*/ (*bContextDataCallback)(const bContext *C,
+                                                       const char *member,
+                                                       bContextDataResult *result);
 
 typedef struct bContextStoreEntry {
   struct bContextStoreEntry *next, *prev;
@@ -213,7 +230,7 @@ ListBase CTX_data_dir_get_ex(const bContext *C,
                              const bool use_rna,
                              const bool use_all);
 ListBase CTX_data_dir_get(const bContext *C);
-int CTX_data_get(
+int /*eContextResult*/ CTX_data_get(
     const bContext *C, const char *member, PointerRNA *r_ptr, ListBase *r_lb, short *r_type);
 
 void CTX_data_id_pointer_set(bContextDataResult *result, struct ID *id);
diff --git a/source/blender/blenkernel/BKE_screen.h b/source/blender/blenkernel/BKE_screen.h
index bcc58ecf2c5..35a3d0415a8 100644
--- a/source/blender/blenkernel/BKE_screen.h
+++ b/source/blender/blenkernel/BKE_screen.h
@@ -26,6 +26,8 @@
 
 #include "RNA_types.h"
 
+#include "BKE_context.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -106,7 +108,7 @@ typedef struct SpaceType {
   void (*gizmos)(void);
 
   /* return context data */
-  int (*context)(const struct bContext *C, const char *member, struct bContextDataResult *result);
+  bContextDataCallback context;
 
   /* Used when we want to replace an ID by another (or NULL). */
   void (*id_remap)(struct ScrArea *area,
@@ -181,7 +183,7 @@ typedef struct ARegionType {
   void (*cursor)(struct wmWindow *win, struct ScrArea *area, struct ARegion *region);
 
   /* return context data */
-  int (*context)(const struct bContext *C, const char *member, struct bContextDataResult *result);
+  bContextDataCallback context;
 
   /* Is called whenever the current visible View2D's region changes.
    *
diff --git a/source/blender/blenkernel/intern/context.c b/source/blender/blenkernel/intern/context.c
index 17ac8d7bedc..2002a49293f 100644
--- a/source/blender/blenkernel/intern/context.c
+++ b/source/blender/blenkernel/intern/context.c
@@ -294,7 +294,7 @@ static void *ctx_wm_python_context_get(const bContext *C,
   return fall_through;
 }
 
-static int ctx_data_get(bContext *C, const char *member, bContextDataResult *result)
+static eContextResult ctx_data_get(bContext *C, const char *member, bContextDataResult *result)
 {
   bScreen *screen;
   ScrArea *area;
@@ -374,7 +374,7 @@ static void *ctx_data_pointer_get(const bContext *C, const char *member)
 {
   bContextDataResult result;
 
-  if (C && ctx_data_get((bContext *)C, member, &result) == 1) {
+  if (C && ctx_data_get((bContext *)C, member, &result) == CTX_RESULT_OK) {
     BLI_assert(result.type == CTX_DATA_TYPE_POINTER);
     return result.ptr.data;
   }
@@ -391,7 +391,7 @@ static int ctx_data_pointer_verify(const bContext *C, const char *member, void *
     *pointer = NULL;
     return 1;
   }
-  if (ctx_data_get((bContext *)C, member, &result) == 1) {
+  if (ctx_data_get((bContext *)C, member, &result) == CTX_RESULT_OK) {
     BLI_assert(result.type == CTX_DATA_TYPE_POINTER);
     *pointer = result.ptr.data;
     return 1;
@@ -405,7 +405,7 @@ static int ctx_data_collection_get(const bContext *C, const char *member, ListBa
 {
   bContextDataResult result;
 
-  if (ctx_data_get((bContext *)C, member, &result) == 1) {
+  if (ctx_data_get((bContext *)C, member, &result) == CTX_RESULT_OK) {
     BLI_assert(result.type == CTX_DATA_TYPE_COLLECTION);
     *list = result.list;
     return 1;
@@ -453,7 +453,7 @@ PointerRNA CTX_data_pointer_get(const bContext *C, const char *member)
 {
   bContextDataResult result;
 
-  if (ctx_data_get((bContext *)C, member, &result) == 1) {
+  if (ctx_data_get((bContext *)C, member, &result) == CTX_RESULT_OK) {
     BLI_assert(result.type == CTX_DATA_TYPE_POINTER);
     return result.ptr;
   }
@@ -495,7 +495,7 @@ ListBase CTX_data_collection_get(const bContext *C, const char *member)
 {
   bContextDataResult result;
 
-  if (ctx_data_get((bContext *)C, member, &result) == 1) {
+  if (ctx_data_get((bContext *)C, member, &result) == CTX_RESULT_OK) {
     BLI_assert(result.type == CTX_DATA_TYPE_COLLECTION);
     return result.list;
   }
@@ -504,14 +504,13 @@ ListBase CTX_data_collection_get(const bContext *C, const char *member)
   return list;
 }
 
-/* 1:found,  -1:found but not set,  0:not found */
-int CTX_data_get(
+int /*eContextResult*/ CTX_data_get(
     const bContext *C, const char *member, PointerRNA *r_ptr, ListBase *r_lb, short *r_type)
 {
   bContextDataResult result;
-  int ret = ctx_data_get((bContext *)C, member, &result);
+  eContextResult ret = ctx_data_get((bContext *)C, member, &result);
 
-  if (ret == 1) {
+  if (ret == CTX_RESULT_OK) {
     *r_ptr = result.ptr;
     *r_lb = result.list;
     *r_type = result.type;