api/buffer: introduce buffer_[gs]et_lines with new indexing convention.

-1 is index past the end, and -2 is the index of the last element.
This eliminates the need for include_start/include_end.

Allow the handling of out-of-bounds to be configurable.

src/nvim/api/buffer.c

@@ -51,8 +51,10 @@ Integer buffer_line_count(Buffer buffer, Error *err)
 /// @return The line string
 String buffer_get_line(Buffer buffer, Integer index, Error *err)
 {
-  String rv = {.size = 0};
+  String rv = { .size = 0 };
-  Array slice = buffer_get_line_slice(buffer, index, index, true, true, err);
+
+  index = convert_index(index);
+  Array slice = buffer_get_lines(buffer, index, index+1, true, err);
 
   if (!err->set && slice.size) {
     rv = slice.items[0].data.string;
@@ -72,8 +74,9 @@ String buffer_get_line(Buffer buffer, Integer index, Error *err)
 void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
 {
   Object l = STRING_OBJ(line);
-  Array array = {.items = &l, .size = 1};
+  Array array = { .items = &l, .size = 1 };
-  buffer_set_line_slice(buffer, index, index, true, true, array, err);
+  index = convert_index(index);
+  buffer_set_lines(buffer, index, index+1, true,  array, err);
 }
 
 /// Deletes a buffer line
@@ -84,7 +87,8 @@ void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
 void buffer_del_line(Buffer buffer, Integer index, Error *err)
 {
   Array array = ARRAY_DICT_INIT;
-  buffer_set_line_slice(buffer, index, index, true, true, array, err);
+  index = convert_index(index);
+  buffer_set_lines(buffer, index, index+1, true, array, err);
 }
 
 /// Retrieves a line range from the buffer
@@ -102,17 +106,49 @@ ArrayOf(String) buffer_get_line_slice(Buffer buffer,
                                  Boolean include_start,
                                  Boolean include_end,
                                  Error *err)
+{
+  start = convert_index(start) + !include_start;
+  end = convert_index(end) + include_end;
+  return buffer_get_lines(buffer, start , end, false, err);
+}
+
+
+/// Retrieves a line range from the buffer
+///
+/// Indexing is zero-based, end-exclusive. Negative indices are interpreted
+/// as length+1+index, i e -1 refers to the index past the end. So to get the
+/// last element set start=-2 and end=-1.
+///
+/// Out-of-bounds indices are clamped to the nearest valid value, unless
+/// `strict_indexing` is set.
+///
+/// @param buffer The buffer handle
+/// @param start The first line index
+/// @param end The last line index (exclusive)
+/// @param strict_indexing whether out-of-bounds should be an error.
+/// @param[out] err Details of an error that may have occurred
+/// @return An array of lines
+ArrayOf(String) buffer_get_lines(Buffer buffer,
+                                 Integer start,
+                                 Integer end,
+                                 Boolean strict_indexing,
+                                 Error *err)
 {
   Array rv = ARRAY_DICT_INIT;
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
-  if (!buf || !inbounds(buf, start)) {
+  if (!buf) {
     return rv;
   }
 
-  start = normalize_index(buf, start) + (include_start ? 0 : 1);
+  bool oob = false;
-  include_end = include_end || (end >= buf->b_ml.ml_line_count);
+  start = normalize_index(buf, start, &oob);
-  end = normalize_index(buf, end) + (include_end ? 1 : 0);
+  end = normalize_index(buf, end, &oob);
+
+  if (strict_indexing && oob) {
+    api_set_error(err, Validation, _("Index out of bounds"));
+    return rv;
+  }
 
   if (start >= end) {
     // Return 0-length array
@@ -152,6 +188,7 @@ end:
   return rv;
 }
 
+
 /// Replaces a line range on the buffer
 ///
 /// @param buffer The buffer handle
@@ -169,6 +206,37 @@ void buffer_set_line_slice(Buffer buffer,
                       Boolean include_end,
                       ArrayOf(String) replacement,
                       Error *err)
+{
+  start = convert_index(start) + !include_start;
+  end = convert_index(end) + include_end;
+  buffer_set_lines(buffer, start, end, false, replacement, err);
+}
+
+
+/// Replaces line range on the buffer
+///
+/// Indexing is zero-based, end-exclusive. Negative indices are interpreted
+/// as length+1+index, i e -1 refers to the index past the end. So to change
+/// or delete the last element set start=-2 and end=-1.
+///
+/// To insert lines at a given index, set both start and end to the same index.
+/// To delete a range of lines, set replacement to an empty array.
+///
+/// Out-of-bounds indices are clamped to the nearest valid value, unless
+/// `strict_indexing` is set.
+///
+/// @param buffer The buffer handle
+/// @param start The first line index
+/// @param end The last line index (exclusive)
+/// @param strict_indexing whether out-of-bounds should be an error.
+/// @param replacement An array of lines to use as replacement
+/// @param[out] err Details of an error that may have occurred
+void buffer_set_lines(Buffer buffer,
+                      Integer start,
+                      Integer end,
+                      Boolean strict_indexing,
+                      ArrayOf(String) replacement,
+                      Error *err)
 {
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
@@ -176,14 +244,15 @@ void buffer_set_line_slice(Buffer buffer,
     return;
   }
 
-  if (!inbounds(buf, start)) {
+  bool oob = false;
+  start = normalize_index(buf, start, &oob);
+  end = normalize_index(buf, end, &oob);
+
+  if (strict_indexing && oob) {
     api_set_error(err, Validation, _("Index out of bounds"));
     return;
   }
 
-  start = normalize_index(buf, start) + (include_start ? 0 : 1);
-  include_end = include_end || (end >= buf->b_ml.ml_line_count);
-  end = normalize_index(buf, end) + (include_end ? 1 : 0);
 
   if (start > end) {
     api_set_error(err,
@@ -467,8 +536,9 @@ void buffer_insert(Buffer buffer,
                    ArrayOf(String) lines,
                    Error *err)
 {
-  bool end_start = lnum < 0;
+  // "lnum" will be the index of the line after inserting,
-  buffer_set_line_slice(buffer, lnum, lnum, !end_start, end_start, lines, err);
+  // no matter if it is negative or not
+  buffer_set_lines(buffer, lnum, lnum, true, lines, err);
 }
 
 /// Return a tuple (row,col) representing the position of the named mark
@@ -632,20 +702,26 @@ static void fix_cursor(linenr_T lo, linenr_T hi, linenr_T extra)
 }
 
 // Normalizes 0-based indexes to buffer line numbers
-static int64_t normalize_index(buf_T *buf, int64_t index)
+static int64_t normalize_index(buf_T *buf, int64_t index, bool *oob)
 {
+  int64_t line_count = buf->b_ml.ml_line_count;
   // Fix if < 0
-  index = index < 0 ?  buf->b_ml.ml_line_count + index : index;
+  index = index < 0 ? line_count + index +1 : index;
+
+  // Check for oob
+  if (index > line_count) {
+    *oob = true;
+    index = line_count;
+  } else if (index < 0) {
+    *oob = true;
+    index = 0;
+  }
   // Convert the index to a vim line number
   index++;
-  // Fix if > line_count
-  index = index > buf->b_ml.ml_line_count ? buf->b_ml.ml_line_count : index;
   return index;
 }
 
-// Returns true if the 0-indexed `index` is within the 1-indexed buffer bounds.
+static int64_t convert_index(int64_t index)
-static bool inbounds(buf_T *buf, int64_t index)
 {
-  linenr_T nlines = buf->b_ml.ml_line_count;
+  return index < 0 ? index - 1 : index;
-  return index >= -nlines && index < nlines;
 }

test/functional/api/buffer_spec.lua

@@ -35,10 +35,11 @@ describe('buffer_* functions', function()
       eq('', curbuf('get_line', 0))
     end)
 
-    it('get_line: out-of-bounds returns empty string', function()
+    it('get_line: out-of-bounds is an error', function()
       curbuf('set_line', 0, 'line1.a')
-      eq('', curbuf('get_line', 1))
+      eq(1, curbuf('line_count')) -- sanity
-      eq('', curbuf('get_line', -2))
+      eq(false, pcall(curbuf, 'get_line', 1))
+      eq(false, pcall(curbuf, 'get_line', -2))
     end)
 
     it('set_line, del_line: out-of-bounds is an error', function()
@@ -68,14 +69,16 @@ describe('buffer_* functions', function()
       eq({}, curbuf('get_line_slice', -4, -5, true, true))
     end)
 
-    it('set_line_slice: out-of-bounds is an error', function()
+    it('set_line_slice: out-of-bounds extends past end', function()
       curbuf('set_line_slice', 0, 0, true, true, {'a', 'b', 'c'})
       eq({'a', 'b', 'c'}, curbuf('get_line_slice', 0, 2, true, true)) --sanity
 
       eq({'c'}, curbuf('get_line_slice', -1, 4, true, true))
       eq({'a', 'b', 'c'}, curbuf('get_line_slice', 0, 5, true, true))
-      eq(false, pcall(curbuf, 'set_line_slice', 4, 5, true, true, {'d'}))
+      curbuf('set_line_slice', 4, 5, true, true, {'d'})
-      eq(false, pcall(curbuf, 'set_line_slice', -4, -5, true, true, {'d'}))
+      eq({'a', 'b', 'c', 'd'}, curbuf('get_line_slice', 0, 5, true, true))
+      curbuf('set_line_slice', -4, -5, true, true, {'e'})
+      eq({'e', 'a', 'b', 'c', 'd'}, curbuf('get_line_slice', 0, 5, true, true))
     end)
 
     it('works', function()