Rewrite utils.df_expr_to_ref() for consistency, add tests

docs/changelog.txt

@@ -78,6 +78,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 - History: added ``dfhack.getCommandHistory(history_id, history_filename)`` and ``dfhack.addCommandToHistory(history_id, history_filename, command)`` so gui scripts can access a commandline history without requiring a terminal.
 - ``helpdb``: database and query interface for DFHack tool help text
 - ``tile-material``: fix the order of declarations. The ``GetTileMat`` function now returns the material as intended (always returned nil before). Also changed the license info, with permission of the original author.
+- ``utils.df_expr_to_ref()``: fixed some errors that could occur when navigating tables
 - ``widgets.EditField``: new ``onsubmit2`` callback attribute is called when the user hits Shift-Enter.
 - ``widgets.EditField``: new function: ``setCursor(position)`` sets the input cursor.
 - ``widgets.EditField``: new attribute: ``ignore_keys`` lets you ignore specified characters if you want to use them as hotkeys

library/lua/utils.lua

@@ -613,13 +613,15 @@ function df_expr_to_ref(expr)
     local obj = df_env[parts[1]]
     for i = 2, #parts do
         local key = tonumber(parts[i]) or parts[i]
-        local cur = obj[key]
-        if i == #parts and ((type(cur) ~= 'userdata') or
-                type(cur) == 'userdata' and getmetatable(cur) == nil) then
-            obj = obj:_field(key)
-        else
-            obj = obj[key]
+        if i == #parts then
+            local ok, ret = pcall(function()
+                return obj:_field(key)
+            end)
+            if ok then
+                return ret
+            end
         end
+        obj = obj[key]
     end
     return obj
 end

test/library/utils.lua

@@ -54,3 +54,40 @@ function test.invert_overwrite()
     expect.eq(i.b, 2)
     expect.eq(i.a, 3)
 end
+
+function test.df_expr_to_ref()
+    -- userdata field
+    expect.eq(utils.df_expr_to_ref('df.global.world.engravings'), df.global.world.engravings)
+    expect.eq(utils.df_expr_to_ref('df.global.world.engravings'), df.global.world:_field('engravings'))
+    -- primitive field
+    expect.eq(utils.df_expr_to_ref('df.global.world.original_save_version'), df.global.world:_field('original_save_version'))
+    -- table field
+    expect.eq(utils.df_expr_to_ref('df.global.world'), df.global.world)
+    expect.eq(utils.df_expr_to_ref('df.global'), df.global)
+    -- table
+    expect.eq(utils.df_expr_to_ref('df'), df)
+
+    -- userdata object
+    expect.eq(utils.df_expr_to_ref('scr'), dfhack.gui.getCurViewscreen())
+
+    local fake_unit
+    mock.patch(dfhack.gui, 'getSelectedUnit', function() return fake_unit end, function()
+        -- lightuserdata field
+        fake_unit = {
+           null_field=df.NULL,
+        }
+        expect.eq(utils.df_expr_to_ref('unit'), fake_unit)
+        expect.eq(utils.df_expr_to_ref('unit.null_field'), fake_unit.null_field)
+
+        dfhack.with_temp_object(df.unit:new(), function(u)
+            fake_unit = u
+
+            -- userdata field
+            expect.eq(utils.df_expr_to_ref('unit.name'), fake_unit.name)
+            expect.eq(utils.df_expr_to_ref('unit.name'), fake_unit:_field('name'))
+
+            -- primitive field
+            expect.eq(utils.df_expr_to_ref('unit.profession'), fake_unit:_field('profession'))
+        end)
+    end)
+end