fix: '\' at end of last line in query no longer discards the instruction

Fixes #3137.

Author: claremacrae

src/Query/Scanner.ts

@@ -69,7 +69,15 @@ export function continueLines(input: string): Statement[] {
 
     let currentStatementRaw = '';
     let currentStatementProcessed = '';
-    for (const inputLine of input.split('\n')) {
+
+    // See https://github.com/obsidian-tasks-group/obsidian-tasks/issues/3137.
+    //      Issue #3137 revealed that if the last line of the query ended in
+    //      a backslash, this function returned without saved the final
+    //      instruction.
+    //      The simplest way to prevent this is to add an extra end-of-line
+    //      to the end of the query, which will get ignored when not needed:
+    const inputWithGuaranteedFinalEOL = input + '\n';
+    for (const inputLine of inputWithGuaranteedFinalEOL.split('\n')) {
         const adjustedLine = adjustLine(inputLine, continuePreviousLine);
         if (continuePreviousLine) {
             currentStatementRaw += '\n' + inputLine;

tests/Query/Query.test.ts

@@ -556,8 +556,7 @@ describe('Query parsing', () => {
         expect(new Query('short mode\nfull').queryLayoutOptions.shortMode).toEqual(false);
     });
 
-    it.failing('should cope with missing end-of-line character in query ending with continuation character', () => {
-        // See https://github.com/obsidian-tasks-group/obsidian-tasks/issues/3137
+    it('should cope with missing end-of-line character in query ending with continuation character - #3137', () => {
         const query = new Query('path includes query.md \\');
         expect(query.filters.length).toEqual(1);
         expect(query.filters[0].instruction).toEqual('path includes query.md');

tests/Query/Scanner.test.ts

@@ -150,6 +150,11 @@ describe('continue_lines', () => {
         expect(continueLinesFlattened(text)).toEqual('description includes one two three four five six');
     });
 
+    it('should preserve last instruction in query that ends in a continuation line = #3137', () => {
+        const text = 'due today \\';
+        expect(continueLinesFlattened(text)).toEqual('due today');
+    });
+
     it('visualise continue_lines', () => {
         const output = `
 input: