fix: Prevent confusing group order for floating points without precision

By imposing an arbitrary 5 decimal places of precision if the 'group by function'
expression returns a non-integer numeric value.

Fixes #3371

Author: claremacrae

src/Query/Filter/FunctionField.ts

@@ -283,6 +283,14 @@ export function groupByFunction(task: Task, arg: GroupingArg, queryContext?: Que
             return [];
         }
 
+        if (typeof result === 'number' && !Number.isInteger(result)) {
+            // Guard against #3371: order of groups, when grouping by "function task.urgency" without specifying precision, is confusing.
+            // Sorting has been found to be unreliable with varying numbers of decimal places.
+            // So to ensure consistent sorting, we round the value to a fixed number of decimals and return it as a string.
+            // This still sorts consistently even when some of the group's values are integers.
+            return [result.toFixed(5)];
+        }
+
         // If there was an error in the expression, like it referred to
         // an unknown task field, result will be undefined, and the call
         // on undefined.toString() will give an exception and a useful error

tests/Query/Filter/FunctionField.test.ts

@@ -522,7 +522,7 @@ describe('FunctionField - grouping return types', () => {
         ['1', ['1']],
         ['0', ['0']],
         ['0 || "No value"', ['No value']],
-        ['1.0765456', ['1.0765456']],
+        ['1.0765456', ['1.07655']],
         ['1.0765456.toFixed(3)', ['1.077']],
         ['["heading1", "heading2"]', ['heading1', 'heading2']], // return two headings, indicating that this task should be displayed twice, once in each heading
         ['[1, 2]', ['1', '2']], // return two headings, that need to be converted to strings

tests/Query/Group/TaskGroups.test.ts

@@ -238,7 +238,7 @@ describe('Grouping tasks', () => {
         `);
     });
 
-    it.failing('sorts raw urgency value groups correctly', () => {
+    it('sorts raw urgency value groups correctly', () => {
         jest.useFakeTimers();
         jest.setSystemTime(new Date('2025-03-07'));
 
@@ -256,10 +256,8 @@ describe('Grouping tasks', () => {
         const grouping = [new FunctionField().createGrouperFromLine('group by function task.urgency')!];
 
         const groups: TaskGroups = makeTasksGroups(grouping, tasks);
-        const groupHeadings = groups.groups.map((group: TaskGroup) => group.groups[0].slice(0, 7));
-
-        expect(groupHeadings).toEqual(['14.8357', '15.75', '15.2928']); // This passes: it shows that the order is illogical (non-ascending).
-        expect(groupHeadings).toEqual(['14.8357', '15.2928', '15.75']); // This fails: it is what users would expect.
+        const groupHeadings = groups.groups.map((group: TaskGroup) => group.groups[0]);
+        expect(groupHeadings).toEqual(['14.83571', '15.29286', '15.75000']);
     });
 
     it('handles tasks matching multiple groups correctly', () => {