r.lake: Reject seed coordinates north or west of the region

raster/CMakeLists.txt

@@ -318,7 +318,7 @@ build_program_in_subdir(
 
 build_program_in_subdir(r.latlong DEPENDS grass_gis grass_raster grass_gproj)
 
-build_program_in_subdir(r.lake DEPENDS grass_gis grass_raster)
+build_program_in_subdir(r.lake DEPENDS grass_gis grass_raster ${LIBM})
 
 build_program_in_subdir(
     r.mask.status

raster/r.lake/Makefile

@@ -4,7 +4,7 @@ MODULE_TOPDIR = ../..
 
 PGM = r.lake
 
-LIBES = $(RASTERLIB) $(GISLIB)
+LIBES = $(RASTERLIB) $(GISLIB) $(MATHLIB)
 DEPENDENCIES = $(RASTERDEP) $(GISDEP)
 
 include $(MODULE_TOPDIR)/include/Make/Module.make

raster/r.lake/main.c

@@ -28,6 +28,7 @@
  *  Kaarliit, shii programma ir veltiita Tev.
  *
  */
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 
@@ -232,8 +233,8 @@ int main(int argc, char *argv[])
 
         G_scan_easting(sdxy_opt->answers[0], &east, G_projection());
         G_scan_northing(sdxy_opt->answers[1], &north, G_projection());
-        start_col = (int)Rast_easting_to_col(east, &window);
-        start_row = (int)Rast_northing_to_row(north, &window);
+        start_col = (int)floor(Rast_easting_to_col(east, &window));
+        start_row = (int)floor(Rast_northing_to_row(north, &window));
 
         if (start_row < 0 || start_row >= rows || start_col < 0 ||
             start_col >= cols)

raster/r.lake/tests/r_lake_test.py

@@ -110,6 +110,34 @@ def test_seed_coordinates_on_region_edge_are_rejected(
     assert "Seed point outside the current region" in error.value.errors
 
 
+@pytest.mark.parametrize(
+    "coordinates",
+    [(25.5, 50.5), (25.5, 50.9), (-0.5, 25.5), (-0.9, 25.5)],
+    ids=["north", "north-almost-one-cell", "west", "west-almost-one-cell"],
+)
+def test_seed_coordinates_less_than_a_cell_outside_are_rejected(
+    session_with_flat_terrain, coordinates
+):
+    """Coordinates north or west of the region are outside it.
+
+    Truncating the converted index towards zero turns the whole interval
+    between -1 and 0 into row or column 0, which hides these coordinates from
+    the check below zero.
+    """
+    tools = Tools(session=session_with_flat_terrain)
+
+    with pytest.raises(ToolError) as error:
+        tools.r_lake(
+            elevation="terrain",
+            water_level=10,
+            lake="lake_out",
+            coordinates=coordinates,
+        )
+
+    assert error.value.returncode == 1
+    assert "Seed point outside the current region" in error.value.errors
+
+
 def test_seed_coordinates_in_last_row_are_accepted(session_with_flat_terrain):
     """Coordinates in the last row are inside the region and fill it."""
     tools = Tools(session=session_with_flat_terrain)
@@ -120,3 +148,18 @@ def test_seed_coordinates_in_last_row_are_accepted(session_with_flat_terrain):
 
     stats = tools.r_univar(map="lake_out", format="json").json
     assert stats["n"] == 2500
+
+
+@pytest.mark.parametrize("coordinates", [(25.5, 50), (0, 25.5)], ids=["north", "west"])
+def test_seed_coordinates_on_north_and_west_edge_are_accepted(
+    session_with_flat_terrain, coordinates
+):
+    """The northern and western edges belong to the first row and column."""
+    tools = Tools(session=session_with_flat_terrain)
+
+    tools.r_lake(
+        elevation="terrain", water_level=10, lake="lake_out", coordinates=coordinates
+    )
+
+    stats = tools.r_univar(map="lake_out", format="json").json
+    assert stats["n"] == 2500