fix(float): make screen*() functions respect floating windows

Resolves neovim#19013.

src/nvim/eval/funcs.c

@@ -66,6 +66,7 @@
 #include "nvim/tag.h"
 #include "nvim/testing.h"
 #include "nvim/ui.h"
+#include "nvim/ui_compositor.h"
 #include "nvim/undo.h"
 #include "nvim/version.h"
 #include "nvim/vim.h"
@@ -8037,13 +8038,17 @@ static void f_screenattr(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
   int row = (int)tv_get_number_chk(&argvars[0], NULL) - 1;
   int col = (int)tv_get_number_chk(&argvars[1], NULL) - 1;
-  if (row < 0 || row >= default_grid.rows
-      || col < 0 || col >= default_grid.cols) {
+
+  ScreenGrid *grid = ui_comp_get_grid_at_coord(row, col);
+  int grid_row = row - grid->comp_row;
+  int grid_col = col - grid->comp_col;
+
+  if (grid_row < 0 || grid_row >= grid->rows
+      || grid_col < 0 || grid_col >= grid->cols) {
     c = -1;
   } else {
-    ScreenGrid *grid = &default_grid;
     screenchar_adjust_grid(&grid, &row, &col);
-    c = grid->attrs[grid->line_offset[row] + col];
+    c = grid->attrs[grid->line_offset[grid_row] + grid_col];
   }
   rettv->vval.v_number = c;
 }
@@ -8055,13 +8060,17 @@ static void f_screenchar(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
   int row = tv_get_number_chk(&argvars[0], NULL) - 1;
   int col = tv_get_number_chk(&argvars[1], NULL) - 1;
-  if (row < 0 || row >= default_grid.rows
-      || col < 0 || col >= default_grid.cols) {
+
+  ScreenGrid *grid = ui_comp_get_grid_at_coord(row, col);
+  int grid_row = row - grid->comp_row;
+  int grid_col = col - grid->comp_col;
+
+  if (grid_row < 0 || grid_row >= grid->rows
+      || grid_col < 0 || grid_col >= grid->cols) {
     c = -1;
   } else {
-    ScreenGrid *grid = &default_grid;
     screenchar_adjust_grid(&grid, &row, &col);
-    c = utf_ptr2char((char *)grid->chars[grid->line_offset[row] + col]);
+    c = utf_ptr2char((char *)grid->chars[grid->line_offset[grid_row] + grid_col]);
   }
   rettv->vval.v_number = c;
 }
@@ -8071,15 +8080,19 @@ static void f_screenchars(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
   int row = tv_get_number_chk(&argvars[0], NULL) - 1;
   int col = tv_get_number_chk(&argvars[1], NULL) - 1;
-  if (row < 0 || row >= default_grid.rows
-      || col < 0 || col >= default_grid.cols) {
+
+  ScreenGrid *grid = ui_comp_get_grid_at_coord(row, col);
+  int grid_row = row - grid->comp_row;
+  int grid_col = col - grid->comp_col;
+
+  if (grid_row < 0 || grid_row >= grid->rows
+      || grid_col < 0 || grid_col >= grid->cols) {
     tv_list_alloc_ret(rettv, 0);
     return;
   }
-  ScreenGrid *grid = &default_grid;
   screenchar_adjust_grid(&grid, &row, &col);
   int pcc[MAX_MCO];
-  int c = utfc_ptr2char(grid->chars[grid->line_offset[row] + col], pcc);
+  int c = utfc_ptr2char(grid->chars[grid->line_offset[grid_row] + grid_col], pcc);
   int composing_len = 0;
   while (pcc[composing_len] != 0) {
     composing_len++;
@@ -8138,13 +8151,17 @@ static void f_screenstring(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   rettv->v_type = VAR_STRING;
   int row = tv_get_number_chk(&argvars[0], NULL) - 1;
   int col = tv_get_number_chk(&argvars[1], NULL) - 1;
-  if (row < 0 || row >= default_grid.rows
-      || col < 0 || col >= default_grid.cols) {
+
+  ScreenGrid *grid = ui_comp_get_grid_at_coord(row, col);
+  int grid_row = row - grid->comp_row;
+  int grid_col = col - grid->comp_col;
+  if (grid_row < 0 || grid_row >= grid->rows
+      || grid_col < 0 || grid_col >= grid->cols) {
     return;
   }
-  ScreenGrid *grid = &default_grid;
+
   screenchar_adjust_grid(&grid, &row, &col);
-  rettv->vval.v_string = (char *)vim_strsave(grid->chars[grid->line_offset[row] + col]);
+  rettv->vval.v_string = (char *)vim_strsave(grid->chars[grid->line_offset[grid_row] + grid_col]);
 }
 
 /// "search()" function

src/nvim/ui_compositor.c

@@ -300,6 +300,18 @@ ScreenGrid *ui_comp_mouse_focus(int row, int col)
   return NULL;
 }
 
+ScreenGrid *ui_comp_get_grid_at_coord(int row, int col)
+{
+  for (ssize_t i = (ssize_t)kv_size(layers) - 1; i > 0; i--) {
+    ScreenGrid *grid = kv_A(layers, i);
+    if (row >= grid->comp_row && row < grid->comp_row + grid->rows
+        && col >= grid->comp_col && col < grid->comp_col + grid->cols) {
+      return grid;
+    }
+  }
+  return &default_grid;
+}
+
 /// Baseline implementation. This is always correct, but we can sometimes
 /// do something more efficient (where efficiency means smaller deltas to
 /// the downstream UI.)

test/functional/vimscript/screenchar_spec.lua

@@ -0,0 +1,77 @@
+local helpers = require('test.functional.helpers')(after_each)
+local clear, eq, meths = helpers.clear, helpers.eq, helpers.meths
+local command, funcs = helpers.command, helpers.funcs
+
+local global_helpers = require('test.helpers')
+local neq = global_helpers.neq
+
+-- Set up two overlapping floating windows
+local setup_floating_windows = function()
+  local base_opts = {
+    relative = 'editor',
+    height = 1,
+    width = 2,
+    anchor = 'NW',
+    style = 'minimal',
+    border = 'none',
+  }
+
+  local bufnr_1 = meths.create_buf(false, true)
+  meths.buf_set_lines(bufnr_1, 0, -1, true, { 'aa' })
+  local opts_1 = global_helpers.tbl_deep_extend('force', { row = 0, col = 0, zindex = 11 }, base_opts)
+  meths.open_win(bufnr_1, false, opts_1)
+
+  local bufnr_2 = meths.create_buf(false, true)
+  meths.buf_set_lines(bufnr_2, 0, -1, true, { 'bb' })
+  local opts_2 = global_helpers.tbl_deep_extend('force', { row = 0, col = 1, zindex = 10 }, base_opts)
+  meths.open_win(bufnr_2, false, opts_2)
+
+  command('redraw')
+end
+
+before_each(function()
+  clear()
+  -- These commands result into visible text `aabc`.
+  -- `aab` - from floating windows, `c` - from text in regular window.
+  meths.buf_set_lines(0, 0, -1, true, { 'cccc' })
+  setup_floating_windows()
+end)
+
+describe('screenattr()', function()
+  it('respects floating windows', function()
+    local attr_1 = funcs.screenattr(1, 1)
+    local attr_2 = funcs.screenattr(1, 2)
+    local attr_3 = funcs.screenattr(1, 3)
+    local attr_4 = funcs.screenattr(1, 4)
+    eq(attr_1, attr_2)
+    eq(attr_1, attr_3)
+    neq(attr_1, attr_4)
+  end)
+end)
+
+describe('screenchar()', function()
+  it('respects floating windows', function()
+    eq(97, funcs.screenchar(1, 1))
+    eq(97, funcs.screenchar(1, 2))
+    eq(98, funcs.screenchar(1, 3))
+    eq(99, funcs.screenchar(1, 4))
+  end)
+end)
+
+describe('screenchars()', function()
+  it('respects floating windows', function()
+    eq({ 97 }, funcs.screenchars(1, 1))
+    eq({ 97 }, funcs.screenchars(1, 2))
+    eq({ 98 }, funcs.screenchars(1, 3))
+    eq({ 99 }, funcs.screenchars(1, 4))
+  end)
+end)
+
+describe('screenstring()', function()
+  it('respects floating windows', function()
+    eq('a', funcs.screenstring(1, 1))
+    eq('a', funcs.screenstring(1, 2))
+    eq('b', funcs.screenstring(1, 3))
+    eq('c', funcs.screenstring(1, 4))
+  end)
+end)