Fix overdependence on start/end lines in diff strategy (#2567)

* Add test for issue #2556

* Fix overdependence on start/end lines in diff strategy

Author: mrubens

src/core/diff/strategies/__tests__/multi-search-replace.test.ts

@@ -1541,7 +1541,7 @@ function five() {
 		})
 	})
 
-	describe("insertion/deletion", () => {
+	describe("deletion", () => {
 		let strategy: MultiSearchReplaceDiffStrategy
 
 		beforeEach(() => {
@@ -1646,126 +1646,6 @@ function five() {
 				}
 			})
 		})
-
-		describe("insertion", () => {
-			it("should insert code at specified line when search block is empty", async () => {
-				const originalContent = `function test() {
-    const x = 1;
-    return x;
-}`
-				const diffContent = `test.ts
-<<<<<<< SEARCH
-:start_line:2
-:end_line:2
--------
-=======
-    console.log("Adding log");
->>>>>>> REPLACE`
-
-				const result = await strategy.applyDiff(originalContent, diffContent, 2, 2)
-				expect(result.success).toBe(true)
-				if (result.success) {
-					expect(result.content).toBe(`function test() {
-    console.log("Adding log");
-    const x = 1;
-    return x;
-}`)
-				}
-			})
-
-			it("should preserve indentation when inserting at nested location", async () => {
-				const originalContent = `function test() {
-    if (true) {
-        const x = 1;
-    }
-}`
-				const diffContent = `test.ts
-<<<<<<< SEARCH
-:start_line:3
-:end_line:3
--------
-=======
-        console.log("Before");
-        console.log("After");
->>>>>>> REPLACE`
-
-				const result = await strategy.applyDiff(originalContent, diffContent, 3, 3)
-				expect(result.success).toBe(true)
-				if (result.success) {
-					expect(result.content).toBe(`function test() {
-    if (true) {
-        console.log("Before");
-        console.log("After");
-        const x = 1;
-    }
-}`)
-				}
-			})
-
-			it("should handle insertion at start of file", async () => {
-				const originalContent = `function test() {
-    return true;
-}`
-				const diffContent = `test.ts
-<<<<<<< SEARCH
-:start_line:1
-:end_line:1
--------
-=======
-// Copyright 2024
-// License: MIT
-
->>>>>>> REPLACE`
-
-				const result = await strategy.applyDiff(originalContent, diffContent, 1, 1)
-				expect(result.success).toBe(true)
-				if (result.success) {
-					expect(result.content).toBe(`// Copyright 2024
-// License: MIT
-
-function test() {
-    return true;
-}`)
-				}
-			})
-
-			it("should handle insertion at end of file", async () => {
-				const originalContent = `function test() {
-    return true;
-}`
-				const diffContent = `test.ts
-<<<<<<< SEARCH
-:start_line:4
-:end_line:4
--------
-=======
-// End of file
->>>>>>> REPLACE`
-
-				const result = await strategy.applyDiff(originalContent, diffContent, 4, 4)
-				expect(result.success).toBe(true)
-				if (result.success) {
-					expect(result.content).toBe(`function test() {
-    return true;
-}
-// End of file`)
-				}
-			})
-
-			it("should error if no start_line is provided for insertion", async () => {
-				const originalContent = `function test() {
-    return true;
-}`
-				const diffContent = `test.ts
-<<<<<<< SEARCH
-=======
-console.log("test");
->>>>>>> REPLACE`
-
-				const result = await strategy.applyDiff(originalContent, diffContent)
-				expect(result.success).toBe(false)
-			})
-		})
 	})
 
 	describe("fuzzy matching", () => {
@@ -1949,6 +1829,98 @@ function three() {
 			}
 		})
 
+		it("should work correctly on this example with line numbers that are slightly off", async () => {
+			const originalContent = `.game-container {
+display: flex;
+flex-direction: column;
+gap: 1rem;
+}
+
+.chess-board-container {
+display: flex;
+gap: 1rem;
+align-items: center;
+}
+
+.overlay {
+position: absolute;
+top: 0;
+left: 0;
+width: 100%;
+height: 100%;
+background-color: rgba(0, 0, 0, 0.5);
+z-index: 999; /* Ensure it's above the board but below the promotion dialog */
+}
+
+.game-container.promotion-active .chess-board,
+.game-container.promotion-active .game-toolbar,
+.game-container.promotion-active .game-info-container {
+filter: blur(2px);
+pointer-events: none; /* Disable clicks on these elements */
+}
+
+.game-container.promotion-active .promotion-dialog {
+z-index: 1000; /* Ensure it's above the overlay */
+pointer-events: auto; /* Enable clicks on the promotion dialog */
+}`
+			const diffContent = `test.ts
+<<<<<<< SEARCH
+:start_line:12
+:end_line:13
+-------
+.overlay {
+=======
+.piece {
+will-change: transform;
+}
+
+.overlay {
+>>>>>>> REPLACE
+`
+
+			const result = await strategy.applyDiff(originalContent, diffContent)
+			expect(result.success).toBe(true)
+			if (result.success) {
+				expect(result.content).toBe(`.game-container {
+display: flex;
+flex-direction: column;
+gap: 1rem;
+}
+
+.chess-board-container {
+display: flex;
+gap: 1rem;
+align-items: center;
+}
+
+.piece {
+will-change: transform;
+}
+
+.overlay {
+position: absolute;
+top: 0;
+left: 0;
+width: 100%;
+height: 100%;
+background-color: rgba(0, 0, 0, 0.5);
+z-index: 999; /* Ensure it's above the board but below the promotion dialog */
+}
+
+.game-container.promotion-active .chess-board,
+.game-container.promotion-active .game-toolbar,
+.game-container.promotion-active .game-info-container {
+filter: blur(2px);
+pointer-events: none; /* Disable clicks on these elements */
+}
+
+.game-container.promotion-active .promotion-dialog {
+z-index: 1000; /* Ensure it's above the overlay */
+pointer-events: auto; /* Enable clicks on the promotion dialog */
+}`)
+			}
+		})
+
 		it("should not find matches outside search range and buffer zone", async () => {
 			const originalContent = `
 function one() {

src/core/diff/strategies/multi-search-replace.ts

@@ -7,8 +7,9 @@ import { ToolUse } from "../../assistant-message"
 const BUFFER_LINES = 40 // Number of extra context lines to show before and after matches
 
 function getSimilarity(original: string, search: string): number {
+	// Empty searches are no longer supported
 	if (search === "") {
-		return 1
+		return 0
 	}
 
 	// Normalize strings by removing extra whitespace but preserve case
@@ -367,7 +368,6 @@ Only use a single line of '=======' between search and replacement content, beca
 		const replacements = matches
 			.map((match) => ({
 				startLine: Number(match[2] ?? 0),
-				endLine: Number(match[4] ?? resultLines.length),
 				searchContent: match[6],
 				replaceContent: match[7],
 			}))
@@ -376,7 +376,6 @@ Only use a single line of '=======' between search and replacement content, beca
 		for (const replacement of replacements) {
 			let { searchContent, replaceContent } = replacement
 			let startLine = replacement.startLine + (replacement.startLine === 0 ? 0 : delta)
-			let endLine = replacement.endLine + delta
 
 			// First unescape any escaped markers in the content
 			searchContent = this.unescapeMarkers(searchContent)
@@ -409,23 +408,16 @@ Only use a single line of '=======' between search and replacement content, beca
 			let searchLines = searchContent === "" ? [] : searchContent.split(/\r?\n/)
 			let replaceLines = replaceContent === "" ? [] : replaceContent.split(/\r?\n/)
 
-			// Validate that empty search requires start line
-			if (searchLines.length === 0 && !startLine) {
+			// Validate that search content is not empty
+			if (searchLines.length === 0) {
 				diffResults.push({
 					success: false,
-					error: `Empty search content requires start_line to be specified\n\nDebug Info:\n- Empty search content is only valid for insertions at a specific line\n- For insertions, specify the line number where content should be inserted`,
+					error: `Empty search content is not allowed\n\nDebug Info:\n- Search content cannot be empty\n- For insertions, provide a specific line using :start_line: and include content to search for\n- For example, match a single line to insert before/after it`,
 				})
 				continue
 			}
 
-			// Validate that empty search requires same start and end line
-			if (searchLines.length === 0 && startLine && endLine && startLine !== endLine) {
-				diffResults.push({
-					success: false,
-					error: `Empty search content requires start_line and end_line to be the same (got ${startLine}-${endLine})\n\nDebug Info:\n- Empty search content is only valid for insertions at a specific line\n- For insertions, use the same line number for both start_line and end_line`,
-				})
-				continue
-			}
+			let endLine = replacement.startLine + searchLines.length - 1
 
 			// Initialize search variables
 			let matchIndex = -1