feat: add configuration for diff truncation (#5073)

docs/config/index.md

@@ -2031,6 +2031,28 @@ export default defineConfig({
 ```
 :::
 
+#### diff.truncateThreshold
+
+- **Type**: `number`
+- **Default**: `0`
+
+The maximum length of diff result to be displayed. Diffs above this threshold will be truncated.
+Truncation won't take effect with default value 0.
+
+#### diff.truncateAnnotation
+
+- **Type**: `string`
+- **Default**: `'... Diff result is truncated'`
+
+Annotation that is output at the end of diff result if it's truncated.
+
+#### diff.truncateAnnotationColor
+
+- **Type**: `DiffOptionsColor = (arg: string) => string`
+- **Default**: `noColor = (string: string): string => string`
+
+Color of truncate annotation, default is output with no color.
+
 ### fakeTimers
 
 - **Type:** `FakeTimerInstallOpts`

packages/utils/src/diff/diffLines.ts

@@ -81,21 +81,24 @@ function printAnnotation({
   return `${aColor(a)}\n${bColor(b)}\n\n`
 }
 
-export function printDiffLines(diffs: Array<Diff>, options: DiffOptionsNormalized): string {
+export function printDiffLines(diffs: Array<Diff>, truncated: boolean, options: DiffOptionsNormalized): string {
   return printAnnotation(options, countChanges(diffs))
-    + (options.expand
-      ? joinAlignedDiffsExpand(diffs, options)
-      : joinAlignedDiffsNoExpand(diffs, options))
+    + (options.expand ? joinAlignedDiffsExpand(diffs, options) : joinAlignedDiffsNoExpand(diffs, options))
+    + (truncated ? options.truncateAnnotationColor(`\n${options.truncateAnnotation}`) : '')
 }
 
 // Compare two arrays of strings line-by-line. Format as comparison lines.
 export function diffLinesUnified(aLines: Array<string>, bLines: Array<string>, options?: DiffOptions): string {
+  const normalizedOptions = normalizeDiffOptions(options)
+  const [diffs, truncated] = diffLinesRaw(
+    isEmptyString(aLines) ? [] : aLines,
+    isEmptyString(bLines) ? [] : bLines,
+    normalizedOptions,
+  )
   return printDiffLines(
-    diffLinesRaw(
-      isEmptyString(aLines) ? [] : aLines,
-      isEmptyString(bLines) ? [] : bLines,
-    ),
-    normalizeDiffOptions(options),
+    diffs,
+    truncated,
+    normalizedOptions,
   )
 }
 
@@ -120,7 +123,7 @@ export function diffLinesUnified2(aLinesDisplay: Array<string>, bLinesDisplay: A
     return diffLinesUnified(aLinesDisplay, bLinesDisplay, options)
   }
 
-  const diffs = diffLinesRaw(aLinesCompare, bLinesCompare)
+  const [diffs, truncated] = diffLinesRaw(aLinesCompare, bLinesCompare, options)
 
   // Replace comparison lines with displayable lines.
   let aIndex = 0
@@ -144,13 +147,16 @@ export function diffLinesUnified2(aLinesDisplay: Array<string>, bLinesDisplay: A
     }
   })
 
-  return printDiffLines(diffs, normalizeDiffOptions(options))
+  return printDiffLines(diffs, truncated, normalizeDiffOptions(options))
 }
 
 // Compare two arrays of strings line-by-line.
-export function diffLinesRaw(aLines: Array<string>, bLines: Array<string>): Array<Diff> {
-  const aLength = aLines.length
-  const bLength = bLines.length
+export function diffLinesRaw(aLines: Array<string>, bLines: Array<string>, options?: DiffOptions): [Array<Diff>, boolean] {
+  const truncate = options?.truncateThreshold ?? false
+  const truncateThreshold = Math.max(Math.floor(options?.truncateThreshold ?? 0), 0)
+  const aLength = truncate ? Math.min(aLines.length, truncateThreshold) : aLines.length
+  const bLength = truncate ? Math.min(bLines.length, truncateThreshold) : bLines.length
+  const truncated = aLength !== aLines.length || bLength !== bLines.length
 
   const isCommon = (aIndex: number, bIndex: number) => aLines[aIndex] === bLines[bIndex]
 
@@ -185,5 +191,5 @@ export function diffLinesRaw(aLines: Array<string>, bLines: Array<string>): Arra
   for (; bIndex !== bLength; bIndex += 1)
     diffs.push(new Diff(DIFF_INSERT, bLines[bIndex]))
 
-  return diffs
+  return [diffs, truncated]
 }

packages/utils/src/diff/diffStrings.ts

@@ -7,8 +7,31 @@
 
 import * as diff from 'diff-sequences'
 import { DIFF_DELETE, DIFF_EQUAL, DIFF_INSERT, Diff } from './cleanupSemantic'
+import type { DiffOptions } from './types'
+
+// platforms compatible
+function getNewLineSymbol(string: string) {
+  return string.includes('\r\n') ? '\r\n' : '\n'
+}
+
+function diffStrings(a: string, b: string, options?: DiffOptions): [Array<Diff>, boolean] {
+  const truncate = options?.truncateThreshold ?? false
+  const truncateThreshold = Math.max(Math.floor(options?.truncateThreshold ?? 0), 0)
+  let aLength = a.length
+  let bLength = b.length
+  if (truncate) {
+    const aMultipleLines = a.includes('\n')
+    const bMultipleLines = b.includes('\n')
+    const aNewLineSymbol = getNewLineSymbol(a)
+    const bNewLineSymbol = getNewLineSymbol(b)
+    // multiple-lines string expects a newline to be appended at the end
+    const _a = aMultipleLines ? `${a.split(aNewLineSymbol, truncateThreshold).join(aNewLineSymbol)}\n` : a
+    const _b = bMultipleLines ? `${b.split(bNewLineSymbol, truncateThreshold).join(bNewLineSymbol)}\n` : b
+    aLength = _a.length
+    bLength = _b.length
+  }
+  const truncated = aLength !== a.length || bLength !== b.length
 
-function diffStrings(a: string, b: string): Array<Diff> {
   const isCommon = (aIndex: number, bIndex: number) => a[aIndex] === b[bIndex]
 
   let aIndex = 0
@@ -34,16 +57,16 @@ function diffStrings(a: string, b: string): Array<Diff> {
   // @ts-expect-error wrong bundling
   const diffSequences = diff.default.default || diff.default
 
-  diffSequences(a.length, b.length, isCommon, foundSubsequence)
+  diffSequences(aLength, bLength, isCommon, foundSubsequence)
 
   // After the last common subsequence, push remaining change items.
-  if (aIndex !== a.length)
+  if (aIndex !== aLength)
     diffs.push(new Diff(DIFF_DELETE, a.slice(aIndex)))
 
-  if (bIndex !== b.length)
+  if (bIndex !== bLength)
     diffs.push(new Diff(DIFF_INSERT, b.slice(bIndex)))
 
-  return diffs
+  return [diffs, truncated]
 }
 
 export default diffStrings

packages/utils/src/diff/normalizeDiffOptions.ts

@@ -12,6 +12,7 @@ import type { DiffOptions, DiffOptionsNormalized } from './types'
 export const noColor = (string: string): string => string
 
 const DIFF_CONTEXT_DEFAULT = 5
+const DIFF_TRUNCATE_THRESHOLD_DEFAULT = 0 // not truncate
 
 function getDefaultOptions(): DiffOptionsNormalized {
   const c = getColors()
@@ -35,6 +36,9 @@ function getDefaultOptions(): DiffOptionsNormalized {
     includeChangeCounts: false,
     omitAnnotationLines: false,
     patchColor: c.yellow,
+    truncateThreshold: DIFF_TRUNCATE_THRESHOLD_DEFAULT,
+    truncateAnnotation: '... Diff result is truncated',
+    truncateAnnotationColor: noColor,
   }
 }
 

packages/utils/src/diff/printDiffs.ts

@@ -32,16 +32,17 @@ export function diffStringsUnified(a: string, b: string, options?: DiffOptions):
     const isMultiline = a.includes('\n') || b.includes('\n')
 
     // getAlignedDiffs assumes that a newline was appended to the strings.
-    const diffs = diffStringsRaw(
+    const [diffs, truncated] = diffStringsRaw(
       isMultiline ? `${a}\n` : a,
       isMultiline ? `${b}\n` : b,
       true, // cleanupSemantic
+      options,
     )
 
     if (hasCommonDiff(diffs, isMultiline)) {
       const optionsNormalized = normalizeDiffOptions(options)
       const lines = getAlignedDiffs(diffs, optionsNormalized.changeColor)
-      return printDiffLines(lines, optionsNormalized)
+      return printDiffLines(lines, truncated, optionsNormalized)
     }
   }
 
@@ -51,11 +52,11 @@ export function diffStringsUnified(a: string, b: string, options?: DiffOptions):
 
 // Compare two strings character-by-character.
 // Optionally clean up small common substrings, also known as chaff.
-export function diffStringsRaw(a: string, b: string, cleanup: boolean): Array<Diff> {
-  const diffs = diffStrings(a, b)
+export function diffStringsRaw(a: string, b: string, cleanup: boolean, options?: DiffOptions): [Array<Diff>, boolean] {
+  const [diffs, truncated] = diffStrings(a, b, options)
 
   if (cleanup)
     cleanupSemantic(diffs) // impure function
 
-  return diffs
+  return [diffs, truncated]
 }

packages/utils/src/diff/types.ts

@@ -27,6 +27,9 @@ export interface DiffOptions {
   omitAnnotationLines?: boolean
   patchColor?: DiffOptionsColor
   compareKeys?: CompareKeys
+  truncateThreshold?: number
+  truncateAnnotation?: string
+  truncateAnnotationColor?: DiffOptionsColor
 }
 
 export interface DiffOptionsNormalized {
@@ -48,4 +51,7 @@ export interface DiffOptionsNormalized {
   includeChangeCounts: boolean
   omitAnnotationLines: boolean
   patchColor: DiffOptionsColor
+  truncateThreshold: number
+  truncateAnnotation: string
+  truncateAnnotationColor: DiffOptionsColor
 }

packages/vitest/src/types/matcher-utils.ts

@@ -31,4 +31,7 @@ export interface DiffOptions {
   patchColor?: Formatter
   // pretty-format type
   compareKeys?: any
+  truncateThreshold?: number
+  truncateAnnotation?: string
+  truncateAnnotationColor?: Formatter
 }