insert-file-contents END enforcement

* src/fileio.c (Finsert_file_contents): When matching text
at buffer start, don’t go past END if specified.

(cherry picked from commit 535ab2d116c259820e18380336913abc57ac0376)

diff --git a/src/fileio.c b/src/fileio.c
index 9c06fd1d25a782b18df18e77a4afa1ae6f45224d..ae6fbb7dc7a9679f775a1ff2392acac25cbcf863 100644 (file)
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4437,11 +4437,27 @@ by calling `format-decode', which see.  */)
         match the text at the beginning of the buffer.  */
       while (true)
        {
-         int nread = emacs_fd_read (fd, read_buf, sizeof read_buf);
+         off_t bytes_to_read = sizeof read_buf;
+         off_t curpos = beg_offset + (same_at_start - BEGV_BYTE);
+         bytes_to_read = min (bytes_to_read, end_offset - curpos);
+         ptrdiff_t nread = (bytes_to_read <= 0
+                            ? 0
+                            : emacs_fd_read (fd, read_buf, bytes_to_read));
          if (nread < 0)
            report_file_error ("Read error", orig_filename);
          else if (nread == 0)
-           break;
+           {
+             file_size_hint = curpos;
+
+             /* Data inserted from the file match the buffer's leading bytes,
+                so there's no need to replace anything.  */
+             emacs_fd_close (fd);
+             clear_unwind_protect (fd_index);
+
+             /* Truncate the buffer to the size of the file.  */
+             del_range_1 (same_at_start, same_at_end, 0, 0);
+             goto handled;
+           }
 
          if (CODING_REQUIRE_DETECTION (&coding))
            {
@@ -4468,17 +4484,6 @@ by calling `format-decode', which see.  */)
          if (bufpos != nread)
            break;
        }
-      /* If the file matches the buffer completely,
-        there's no need to replace anything.  */
-      if (same_at_start - BEGV_BYTE == end_offset - beg_offset)
-       {
-         emacs_fd_close (fd);
-         clear_unwind_protect (fd_index);
-
-         /* Truncate the buffer to the size of the file.  */
-         del_range_1 (same_at_start, same_at_end, 0, 0);
-         goto handled;
-       }
 
       /* Count how many chars at the end of the file
         match the text at the end of the buffer.  But, if we have