API: Extract error boilerplate into a macro

src/api/buffer.c

@@ -68,9 +68,7 @@ void buffer_set_line(Buffer buffer, int64_t index, Object line, Error *err)
   }
 
   if (line.type != kObjectTypeNil && line.type != kObjectTypeString) {
-    char msg[] = "Invalid line";
+    set_api_error("Invalid line", err);
-    strncpy(err->msg, msg, sizeof(err->msg));
-    err->set = true;
     return;
   }
 
@@ -86,14 +84,10 @@ void buffer_set_line(Buffer buffer, int64_t index, Object line, Error *err)
 
     if (u_savedel(index, 1L) == FAIL) {
       // Failed to save undo
-      char msg[] = "Cannot save undo information";
+      set_api_error("Cannot save undo information", err);
-      strncpy(err->msg, msg, sizeof(err->msg));
-      err->set = true;
     } else if (ml_delete(index, FALSE) == FAIL) {
       // Failed to delete
-      char msg[] = "Cannot delete the line";
+      set_api_error("Cannot delete the line", err);
-      strncpy(err->msg, msg, sizeof(err->msg));
-      err->set = true;
     } else {
       restore_win_for_buf(save_curwin, save_curtab, save_curbuf);
       // Success
@@ -117,14 +111,10 @@ void buffer_set_line(Buffer buffer, int64_t index, Object line, Error *err)
 
     if (u_savesub(index) == FAIL) {
       // Failed to save undo
-      char msg[] = "Cannot save undo information";
+      set_api_error("Cannot save undo information", err);
-      strncpy(err->msg, msg, sizeof(err->msg));
-      err->set = true;
     } else if (ml_replace(index, (char_u *)string, FALSE) == FAIL) {
       // Failed to replace
-      char msg[] = "Cannot replace line";
+      set_api_error("Cannot replace line", err);
-      strncpy(err->msg, msg, sizeof(err->msg));
-      err->set = true;
       free(string);
     } else {
       // Success
@@ -213,9 +203,7 @@ static buf_T *find_buffer(Buffer buffer, Error *err)
   buf_T *buf = buflist_findnr(buffer);
 
   if (buf == NULL) {
-    char msg[] = "Invalid buffer id";
+    set_api_error("Invalid buffer id", err);
-    strncpy(err->msg, msg, sizeof(err->msg));
-    err->set = true;
   }
 
   return buf;

src/api/helpers.c

@@ -21,15 +21,12 @@ bool try_end(Error *err)
   did_emsg = false;
 
   if (got_int) {
-    const char msg[] = "Keyboard interrupt";
-
     if (did_throw) {
       // If we got an interrupt, discard the current exception 
       discard_current_exception();
     }
 
-    strncpy(err->msg, msg, sizeof(err->msg));
+    set_api_error("Keyboard interrupt", err);
-    err->set = true;
     got_int = false;
   } else if (msg_list != NULL && *msg_list != NULL) {
     int should_free;
@@ -45,8 +42,7 @@ bool try_end(Error *err)
       free(msg);
     }
   } else if (did_throw) {
-    strncpy(err->msg, (char *)current_exception->value, sizeof(err->msg));
+    set_api_error((char *)current_exception->value, err);
-    err->set = true;
   }
 
   return err->set;

src/api/helpers.h

@@ -5,6 +5,12 @@
 
 #include "api/defs.h"
 
+#define set_api_error(message, err)                \
+  do {                                             \
+    strncpy(err->msg, message, sizeof(err->msg));  \
+    err->set = true;                               \
+  } while (0)
+
 /// Start block that may cause vimscript exceptions
 void try_start(void);
 

src/api/vim.c

@@ -127,9 +127,7 @@ void vim_change_directory(String dir, Error *err)
 
   if (vim_chdir((char_u *)string)) {
     if (!try_end(err)) {
-      char msg[] = "failed to change directory";
+      set_api_error("failed to change directory", err);
-      strncpy(err->msg, msg, sizeof(err->msg));
-      err->set = true;
     }
     return;
   }