Cody: Limit completions to 2 lines in single line mode (#276)

This commit limits code completions to 2 lines when in single line mode,
to avoid cluttering the editor with too many lines.

Added unit tests for:

- Completing up to 2 lines
- Completing 1 line if the second line is indented

This fixes a UX issue where inline completions look like a truncated
multi-line completion, e.g.:

<img width="758" alt="Screenshot 2023-07-17 at 14 20 48"
src="https://github.com/sourcegraph/cody/assets/458591/062048fc-c332-4aca-9feb-187eeed35242">


<!-- All pull requests REQUIRE a test plan:

https://docs.sourcegraph.com/dev/background-information/testing_principles
-->

Author: philipp-spiess

vscode/src/completions/completion.test.ts

@@ -234,6 +234,47 @@ describe('Cody completions', () => {
         `)
     })
 
+    it('completes up to two lines in single line mode', async () => {
+        const { completions } = await complete(
+            `
+        function test() {
+            console.log(1);
+            ${CURSOR_MARKER}
+        }
+        `,
+            [createCompletionResponse('console.log(2);\n    console.log(3);\n    console.log(4);')]
+        )
+
+        expect(completions).toMatchInlineSnapshot(`
+          [
+            InlineCompletionItem {
+              "insertText": "console.log(2);
+              console.log(3);",
+            },
+          ]
+        `)
+    })
+
+    it('only complete one line if the second line is indented in single line mode', async () => {
+        const { completions } = await complete(
+            `
+        function test() {
+            console.log(1);
+            ${CURSOR_MARKER}
+        }
+        `,
+            [createCompletionResponse('if (true) {\n        console.log(3);\n    }\n    console.log(4);')]
+        )
+
+        expect(completions).toMatchInlineSnapshot(`
+          [
+            InlineCompletionItem {
+              "insertText": "if (true) {",
+            },
+          ]
+        `)
+    })
+
     it('completes a single-line at the middle of a sentence', async () => {
         const { completions } = await complete(`function bubbleSort(${CURSOR_MARKER})`, [
             createCompletionResponse('array) {'),

vscode/src/completions/providers/anthropic.ts

@@ -11,11 +11,12 @@ import {
     extractFromCodeBlock,
     fixBadCompletionStart,
     getHeadAndTail,
+    indentation,
     OPENING_CODE_TAG,
     PrefixComponents,
     trimStartUntilNewline,
 } from '../text-processing'
-import { batchCompletions, messagesToText } from '../utils'
+import { batchCompletions, lastNLines, messagesToText } from '../utils'
 
 import { Provider, ProviderConfig, ProviderOptions } from './provider'
 
@@ -112,6 +113,7 @@ export class AnthropicProvider extends Provider {
 
     private postProcess(rawResponse: string): string {
         let completion = extractFromCodeBlock(rawResponse)
+        const startIndentation = indentation(lastNLines(this.prefix, 1) + completion.split('\n')[0])
 
         const trimmedPrefixContainNewline = this.prefix.slice(this.prefix.trimEnd().length).includes('\n')
         if (trimmedPrefixContainNewline) {
@@ -127,9 +129,16 @@ export class AnthropicProvider extends Provider {
 
         // Remove incomplete lines in single-line completions
         if (this.multilineMode === null) {
-            const allowedNewlines = 2
+            let allowedNewlines = 2
             const lines = completion.split('\n')
             if (lines.length >= allowedNewlines) {
+                // Only select two lines if they have the same indentation, otherwise only show one
+                // line. This will then most-likely trigger a multi-line completion after accepting
+                // and result in a better experience.
+                if (lines.length > 1 && startIndentation !== indentation(lines[1])) {
+                    allowedNewlines = 1
+                }
+
                 completion = lines.slice(0, allowedNewlines).join('\n')
             }
         }