Swadhin Biswas feat: implement mervelas cli engine, built-in tools, and reactive UI · 4/3/2026
0358986
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import { type StructuredPatchHunk, structuredPatch } from 'diff'
import { logEvent } from 'src/services/analytics/index.js'
import { getLocCounter } from '../bootstrap/state.js'
import { addToTotalLinesChanged } from '../cost-tracker.js'
import type { FileEdit } from '../tools/FileEditTool/types.js'
import { count } from './array.js'
import { convertLeadingTabsToSpaces } from './file.js'
export const CONTEXT_LINES = 3
export const DIFF_TIMEOUT_MS = 5_000
/**
* Shifts hunk line numbers by offset. Use when getPatchForDisplay received
* a slice of the file (e.g. readEditContext) rather than the whole file —
* callers pass `ctx.lineOffset - 1` to convert slice-relative to file-relative.
*/
export function adjustHunkLineNumbers(
hunks: StructuredPatchHunk[],
offset: number,
): StructuredPatchHunk[] {
if (offset === 0) return hunks
return hunks.map(h => ({
...h,
oldStart: h.oldStart + offset,
newStart: h.newStart + offset,
}))
}
// For some reason, & confuses the diff library, so we replace it with a token,
// then substitute it back in after the diff is computed.
const AMPERSAND_TOKEN = '<<:AMPERSAND_TOKEN:>>'
const DOLLAR_TOKEN = '<<:DOLLAR_TOKEN:>>'
function escapeForDiff(s: string): string {
return s.replaceAll('&', AMPERSAND_TOKEN).replaceAll('$', DOLLAR_TOKEN)
}
function unescapeFromDiff(s: string): string {
return s.replaceAll(AMPERSAND_TOKEN, '&').replaceAll(DOLLAR_TOKEN, '$')
}
/**
* Count lines added and removed in a patch and update the total
* For new files, pass the content string as the second parameter
* @param patch Array of diff hunks
* @param newFileContent Optional content string for new files
*/
export function countLinesChanged(
patch: StructuredPatchHunk[],
newFileContent?: string,
): void {
let numAdditions = 0
let numRemovals = 0
if (patch.length === 0 && newFileContent) {
// For new files, count all lines as additions
numAdditions = newFileContent.split(/\r?\n/).length
} else {
numAdditions = patch.reduce(
(acc, hunk) => acc + count(hunk.lines, _ => _.startsWith('+')),
0,
)
numRemovals = patch.reduce(
(acc, hunk) => acc + count(hunk.lines, _ => _.startsWith('-')),
0,
)
}
addToTotalLinesChanged(numAdditions, numRemovals)
getLocCounter()?.add(numAdditions, { type: 'added' })
getLocCounter()?.add(numRemovals, { type: 'removed' })
logEvent('tengu_file_changed', {
lines_added: numAdditions,
lines_removed: numRemovals,
})
}
export function getPatchFromContents({
filePath,
oldContent,
newContent,
ignoreWhitespace = false,
singleHunk = false,
}: {
filePath: string
oldContent: string
newContent: string
ignoreWhitespace?: boolean
singleHunk?: boolean
}): StructuredPatchHunk[] {
const result = structuredPatch(
filePath,
filePath,
escapeForDiff(oldContent),
escapeForDiff(newContent),
undefined,
undefined,
{
ignoreWhitespace,
context: singleHunk ? 100_000 : CONTEXT_LINES,
timeout: DIFF_TIMEOUT_MS,
},
)
if (!result) {
return []
}
return result.hunks.map(_ => ({
..._,
lines: _.lines.map(unescapeFromDiff),
}))
}
/**
* Get a patch for display with edits applied
* @param filePath The path to the file
* @param fileContents The contents of the file
* @param edits An array of edits to apply to the file
* @param ignoreWhitespace Whether to ignore whitespace changes
* @returns An array of hunks representing the diff
*
* NOTE: This function will return the diff with all leading tabs
* rendered as spaces for display
*/
export function getPatchForDisplay({
filePath,
fileContents,
edits,
ignoreWhitespace = false,
}: {
filePath: string
fileContents: string
edits: FileEdit[]
ignoreWhitespace?: boolean
}): StructuredPatchHunk[] {
const preparedFileContents = escapeForDiff(
convertLeadingTabsToSpaces(fileContents),
)
const result = structuredPatch(
filePath,
filePath,
preparedFileContents,
edits.reduce((p, edit) => {
const { old_string, new_string } = edit
const replace_all = 'replace_all' in edit ? edit.replace_all : false
const escapedOldString = escapeForDiff(
convertLeadingTabsToSpaces(old_string),
)
const escapedNewString = escapeForDiff(
convertLeadingTabsToSpaces(new_string),
)
if (replace_all) {
return p.replaceAll(escapedOldString, () => escapedNewString)
} else {
return p.replace(escapedOldString, () => escapedNewString)
}
}, preparedFileContents),
undefined,
undefined,
{
context: CONTEXT_LINES,
ignoreWhitespace,
timeout: DIFF_TIMEOUT_MS,
},
)
if (!result) {
return []
}
return result.hunks.map(_ => ({
..._,
lines: _.lines.map(unescapeFromDiff),
}))
}