scan: fix nil filters

Before this patch, some nil conditions failed with internal filter
library build error. This patch fixes this internal error, as well as
normalize filters to behave similar to core indexes.

The logic in core Tarantool select is as follows. `nil` condition in
index select is an absence of condition, thus all data is returned
disregarding the condition (condition may affect the order). `box.NULL`
condition is a condition for the null value -- in case of EQ,
only records with null index value are returned, in case of GT,
all non-null values are returned since nulls are in the beginning of an
index and so on. `nil`s and `box.NULL`s in tuple are both satisfy
`box.NULL` equity.

After this patch, `nil` filter condition is treated as no condition.
This is a breaking change since conditions for `'>'` and `'<'`
operator with `nil` operand had resulted with empty response
before this patch. But since it was inconsistent with scanning index
conditions and wasn't intentional, we change it here.

Closes #422

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   non-iterating indexes (#373).
 * Passing errors from storages for merger operations (`crud.select`,
   `crud.pairs`, `readview:select`, `readview:pairs`) (#423).
+* Working with `nil` operand conditions in case of non-indexed fields or
+  non-iterating indexes (#422).
 
 ## [1.4.3] - 05-02-24
 

crud/compare/filters.lua

@@ -345,9 +345,14 @@ local function gen_eq_func_code(func_name, cond, func_args_code)
     local header = LIB_FUNC_HEADER_TEMPLATE:format(func_name, func_args_code)
     table.insert(func_code_lines, header)
 
-    local return_line = string.format(
-        '    return %s', concat_conditions(eq_conds, 'and')
-    )
+    local return_line
+    if #eq_conds > 0 then
+        return_line = string.format(
+            '    return %s', concat_conditions(eq_conds, 'and')
+        )
+    else  -- nil condition is treated as no condition
+        return_line = '    return true'
+    end
     table.insert(func_code_lines, return_line)
 
     table.insert(func_code_lines, 'end')
@@ -398,18 +403,23 @@ local function gen_cmp_array_func_code(operator, func_name, cond, func_args_code
     local results = results_by_operators[operator]
     assert(results ~= nil)
 
-    for i = 1, #eq_conds do
-        local comp_value_code = table.concat({
-            string.format('    if %s then return %s end', lt_conds[i], results.le),
-            string.format('    if not %s then return %s end', eq_conds[i], results.not_eq),
-            '',
-        }, '\n')
+    if #eq_conds > 0 then
+        for i = 1, #eq_conds do
+            local comp_value_code = table.concat({
+                string.format('    if %s then return %s end', lt_conds[i], results.le),
+                string.format('    if not %s then return %s end', eq_conds[i], results.not_eq),
+                '',
+            }, '\n')
 
-        table.insert(func_code_lines, comp_value_code)
-    end
+            table.insert(func_code_lines, comp_value_code)
+        end
 
-    local return_code = ('    return %s'):format(results.default)
-    table.insert(func_code_lines, return_code)
+        local return_code = ('    return %s'):format(results.default)
+        table.insert(func_code_lines, return_code)
+    else  -- nil condition is treated as no condition
+        local return_line = '    return true'
+        table.insert(func_code_lines, return_line)
+    end
 
     table.insert(func_code_lines, 'end')
 

test/integration/count_test.lua

@@ -893,3 +893,11 @@ for case_name_template, case in pairs(gh_373_types_cases) do
         case(g, read_impl)
     end
 end
+
+for case_name_template, case in pairs(read_scenario.gh_422_nullability_cases) do
+    local case_name = 'test_' .. case_name_template:format('count')
+
+    pgroup[case_name] = function(g)
+        case(g, read_impl)
+    end
+end

test/integration/pairs_readview_test.lua

@@ -936,3 +936,11 @@ pgroup.after_test(
     'test_pairs_merger_process_storage_error',
     read_scenario.after_merger_process_storage_error
 )
+
+for case_name_template, case in pairs(read_scenario.gh_422_nullability_cases) do
+    local case_name = 'test_' .. case_name_template:format('pairs')
+
+    pgroup[case_name] = function(g)
+        case(g, read_impl)
+    end
+end

test/integration/pairs_test.lua

@@ -944,3 +944,11 @@ pgroup.after_test(
     'test_pairs_merger_process_storage_error',
     read_scenario.after_merger_process_storage_error
 )
+
+for case_name_template, case in pairs(read_scenario.gh_422_nullability_cases) do
+    local case_name = 'test_' .. case_name_template:format('pairs')
+
+    pgroup[case_name] = function(g)
+        case(g, read_impl)
+    end
+end