Add a typescript rule so that array<T>[i] is T | undefined

Because i could be out of bounds (or even: not an integer).

This rule is sometimes really annoying (some call it pedantic), but I
think it can help find bugs.

I'm enabling it as a distinct PR, before a bigger PR where I upgrade
hightable, and need to add code to sort the rows along multiple columns,
where I prefer to have this rule enabled, as in hightable.

Author: severo

src/components/Cell.tsx

@@ -38,12 +38,20 @@ export default function CellView({ source, row, col, config }: CellProps) {
         setProgress(0.75)
         const df = parquetDataFrame(from, metadata)
         const asyncRows = df.rows({ start: row, end: row + 1 })
-        if (asyncRows.length !== 1) {
+        if (asyncRows.length > 1 || !(0 in asyncRows)) {
           throw new Error(`Expected 1 row, got ${asyncRows.length}`)
         }
         const asyncRow = asyncRows[0]
         // Await cell data
-        const text = await asyncRow.cells[df.header[col]].then(stringify)
+        const columnName = df.header[col]
+        if (columnName === undefined) {
+          throw new Error(`Column name missing at index col=${col}`)
+        }
+        const asyncCell = asyncRow.cells[columnName]
+        if (asyncCell === undefined) {
+          throw new Error(`Cell missing at column ${columnName}`)
+        }
+        const text = await asyncCell.then(stringify)
         setText(text)
         setError(undefined)
       } catch (error) {

src/components/Folder.tsx

@@ -47,7 +47,7 @@ export default function Folder({ source, config }: FolderProps) {
         setSearchQuery('')
       } else if (e.key === 'Enter') {
         // if there is only one result, view it
-        if (filtered?.length === 1) {
+        if (filtered?.length === 1 && 0 in filtered) {
           const key = join(source.prefix, filtered[0].name)
           if (key.endsWith('/')) {
             // clear search because we're about to change folder

src/components/Markdown.tsx

@@ -27,7 +27,7 @@ function parseMarkdown(text: string): Token[] {
     const line = lines[i]
 
     // Skip blank lines
-    if (line.trim() === '') {
+    if (line === undefined || line.trim() === '') {
       i++
       continue
     }
@@ -36,9 +36,13 @@ function parseMarkdown(text: string): Token[] {
     if (line.startsWith('```')) {
       const language = line.slice(3).trim() || undefined
       i++
-      const codeLines = []
-      while (i < lines.length && !lines[i].startsWith('```')) {
-        codeLines.push(lines[i])
+      const codeLines: string[] = []
+      while (i < lines.length && !lines[i]?.startsWith('```')) {
+        const currentLine = lines[i]
+        if (currentLine === undefined) {
+          throw new Error(`Line is undefined at index ${i}.`)
+        }
+        codeLines.push(currentLine)
         i++
       }
       i++ // skip the closing ```
@@ -48,7 +52,10 @@ function parseMarkdown(text: string): Token[] {
 
     // Heading
     const headingMatch = /^(#{1,6})\s+(.*)/.exec(line)
-    if (headingMatch) {
+    if (headingMatch !== null) {
+      if (!(1 in headingMatch) || !(2 in headingMatch)) {
+        throw new Error('Missing entries in regex matches')
+      }
       const level = headingMatch[1].length
       tokens.push({
         type: 'heading',
@@ -61,7 +68,10 @@ function parseMarkdown(text: string): Token[] {
 
     // List (ordered or unordered)
     const listMatch = /^(\s*)([-*+]|\d+\.)\s+(.*)/.exec(line)
-    if (listMatch) {
+    if (listMatch !== null) {
+      if (!(1 in listMatch) || !(2 in listMatch)) {
+        throw new Error('Missing entries in regex matches')
+      }
       const baseIndent = listMatch[1].length
       const ordered = /^\d+\./.test(listMatch[2])
       const [items, newIndex] = parseList(lines, i, baseIndent)
@@ -72,9 +82,13 @@ function parseMarkdown(text: string): Token[] {
 
     // Blockquote
     if (line.startsWith('>')) {
-      const quoteLines = []
-      while (i < lines.length && lines[i].startsWith('>')) {
-        quoteLines.push(lines[i].replace(/^>\s?/, ''))
+      const quoteLines: string[] = []
+      while (i < lines.length && lines[i]?.startsWith('>')) {
+        const line = lines[i]
+        if (line === undefined) {
+          throw new Error(`Index ${i} not found in lines`)
+        }
+        quoteLines.push(line.replace(/^>\s?/, ''))
         i++
       }
       tokens.push({
@@ -85,9 +99,13 @@ function parseMarkdown(text: string): Token[] {
     }
 
     // Paragraph
-    const paraLines = []
-    while (i < lines.length && lines[i].trim() !== '') {
-      paraLines.push(lines[i])
+    const paraLines: string[] = []
+    while (i < lines.length && lines[i]?.trim() !== '') {
+      const line = lines[i]
+      if (line === undefined) {
+        throw new Error(`Index ${i} not found in lines`)
+      }
+      paraLines.push(line)
       i++
     }
     tokens.push({
@@ -104,16 +122,18 @@ function parseList(lines: string[], start: number, baseIndent: number): [Token[]
   let i = start
 
   while (i < lines.length) {
+    const line = lines[i]
+
     // End of list if blank line or no more lines
-    if (lines[i].trim() === '') {
+    if (line === undefined || line.trim() === '') {
       i++
       continue
     }
 
     // This matches a new top-level bullet/number for the list
-    const match = /^(\s*)([-*+]|\d+\.)\s+(.*)/.exec(lines[i])
+    const match = /^(\s*)([-*+]|\d+\.)\s+(.*)/.exec(line)
     // If we don't find a bullet/number at the same indent, break out
-    if (!match || match[1].length !== baseIndent) {
+    if (match === null || !(1 in match) || match[1].length !== baseIndent || !(3 in match)) {
       break
     }
 
@@ -130,7 +150,7 @@ function parseList(lines: string[], start: number, baseIndent: number): [Token[]
     // Now parse subsequent indented lines as sub-items or sub-blocks
     while (i < lines.length) {
       const subline = lines[i]
-      if (subline.trim() === '') {
+      if (subline === undefined || subline.trim() === '') {
         i++
         continue
       }
@@ -141,9 +161,13 @@ function parseList(lines: string[], start: number, baseIndent: number): [Token[]
           // If it’s a fenced code block, parse until closing fence
           const language = trimmed.slice(3).trim() || undefined
           i++
-          const codeLines = []
-          while (i < lines.length && !lines[i].trimStart().startsWith('```')) {
-            codeLines.push(lines[i])
+          const codeLines: string[] = []
+          while (i < lines.length && !lines[i]?.trimStart().startsWith('```')) {
+            const line = lines[i]
+            if (line === undefined) {
+              throw new Error(`Line is undefined at index ${i}`)
+            }
+            codeLines.push(line)
             i++
           }
           i++ // skip the closing ```
@@ -157,7 +181,7 @@ function parseList(lines: string[], start: number, baseIndent: number): [Token[]
 
         // Check for nested list
         const sublistMatch = /^(\s*)([-*+]|\d+\.)\s+(.*)/.exec(subline)
-        if (sublistMatch && sublistMatch[1].length > baseIndent) {
+        if (sublistMatch && 1 in sublistMatch && sublistMatch[1].length > baseIndent && 2 in sublistMatch) {
           const newBaseIndent = sublistMatch[1].length
           const ordered = /^\d+\./.test(sublistMatch[2])
           const [subItems, newIndex] = parseList(lines, i, newBaseIndent)
@@ -253,7 +277,11 @@ function parseInlineRecursive(text: string, stop?: string): [Token[], number] {
       const [linkTextTokens, consumed] = parseInlineRecursive(text.slice(i), ']')
       i += consumed
       if (i >= text.length || text[i] !== ']') {
-        tokens.push({ type: 'text', content: text[start] })
+        const startText = text[start]
+        if (startText === undefined) {
+          throw new Error(`Text is undefined at index ${start}`)
+        }
+        tokens.push({ type: 'text', content: startText })
         continue
       }
       i++ // skip ']'
@@ -285,7 +313,11 @@ function parseInlineRecursive(text: string, stop?: string): [Token[], number] {
       i++
       let code = ''
       while (i < text.length && text[i] !== '`') {
-        code += text[i]
+        const character = text[i]
+        if (character === undefined) {
+          throw new Error(`Character is undefined at index ${i}`)
+        }
+        code += character
         i++
       }
       i++
@@ -311,10 +343,18 @@ function parseInlineRecursive(text: string, stop?: string): [Token[], number] {
       if (delimiter === '*') {
         let j = i - 1
         while (j >= 0 && text[j] === ' ') j--
-        const prevIsDigit = j >= 0 && /\d/.test(text[j])
+        const characterAtJ = text[j]
+        if (characterAtJ === undefined) {
+          throw new Error(`Character at index ${j} is undefined`)
+        }
+        const prevIsDigit = j >= 0 && /\d/.test(characterAtJ)
         let k = i + 1
         while (k < text.length && text[k] === ' ') k++
-        const nextIsDigit = k < text.length && /\d/.test(text[k])
+        const characterAtK = text[k]
+        if (characterAtK === undefined) {
+          throw new Error(`Character at index ${j} is undefined`)
+        }
+        const nextIsDigit = k < text.length && /\d/.test(characterAtK)
         if (prevIsDigit && nextIsDigit) {
           tokens.push({ type: 'text', content: delimiter })
           i++

src/components/viewers/CellPanel.tsx

@@ -23,12 +23,21 @@ export default function CellPanel({ df, row, col, setProgress, setError, onClose
       try {
         setProgress(0.5)
         const asyncRows = df.rows({ start: row, end: row + 1 })
-        if (asyncRows.length !== 1) {
+        if (asyncRows.length > 1 || !(0 in asyncRows)) {
           throw new Error(`Expected 1 row, got ${asyncRows.length}`)
         }
         const asyncRow = asyncRows[0]
         // Await cell data
-        const text = await asyncRow.cells[df.header[col]].then(stringify)
+        const columnName = df.header[col]
+        if (columnName === undefined) {
+          throw new Error(`Column name missing at index col=${col}`)
+        }
+        const asyncCell = asyncRow.cells[columnName]
+        if (asyncCell === undefined) {
+          throw new Error(`Cell missing at column ${columnName}`)
+        }
+        /* TODO(SL): use the same implementation of stringify, here and in Cell.tsx */
+        const text = await asyncCell.then(cell => stringify(cell as unknown) ?? '{}')
         setText(text)
       } catch (error) {
         setError(error as Error)

src/components/viewers/ImageView.tsx

@@ -70,13 +70,13 @@ export default function ImageView({ source, setError }: ViewerProps) {
 function arrayBufferToBase64(buffer: ArrayBuffer): string {
   let binary = ''
   const bytes = new Uint8Array(buffer)
-  for (let i = 0; i < bytes.byteLength; i++) {
-    binary += String.fromCharCode(bytes[i])
+  for (const byte of bytes) {
+    binary += String.fromCharCode(byte)
   }
   return btoa(binary)
 }
 
 function contentType(filename: string): string {
   const ext = filename.split('.').pop() ?? ''
-  return contentTypes[ext] || 'image/png'
+  return contentTypes[ext] ?? 'image/png'
 }

src/lib/tableProvider.ts

@@ -17,20 +17,33 @@ export function parquetDataFrame(from: AsyncBufferFrom, metadata: FileMetaData):
 
   function fetchRowGroup(groupIndex: number) {
     if (!groups[groupIndex]) {
-      const rowStart = groupEnds[groupIndex - 1] || 0
+      const rowStart = groupEnds[groupIndex - 1] ?? 0
       const rowEnd = groupEnds[groupIndex]
+      if (rowEnd === undefined) {
+        throw new Error(`Missing groupEnd for groupIndex: ${groupIndex}`)
+      }
       // Initialize with resolvable promises
       for (let i = rowStart; i < rowEnd; i++) {
         data[i] = resolvableRow(header)
       }
       parquetQueryWorker({ from, metadata, rowStart, rowEnd })
         .then((groupData) => {
           for (let i = rowStart; i < rowEnd; i++) {
-            data[i]?.index.resolve(i)
-            for (const [key, value] of Object.entries(
-              groupData[i - rowStart]
-            )) {
-              data[i]?.cells[key].resolve(value)
+            const dataRow = data[i]
+            if (dataRow === undefined) {
+              throw new Error(`Missing data row for index ${i}`)
+            }
+            dataRow.index.resolve(i)
+            const row = groupData[i - rowStart]
+            if (row === undefined) {
+              throw new Error(`Missing row in groupData for index: ${i - rowStart}`)
+            }
+            for (const [key, value] of Object.entries(row)) {
+              const cell = dataRow.cells[key]
+              if (cell === undefined) {
+                throw new Error(`Missing column in dataRow for column ${key}`)
+              }
+              cell.resolve(value)
             }
           }
         })
@@ -68,19 +81,31 @@ export function parquetDataFrame(from: AsyncBufferFrom, metadata: FileMetaData):
           // Re-assemble data in sorted order into wrapped
           for (let i = start; i < end; i++) {
             const index = indices[i]
+            if (index === undefined) {
+              throw new Error(`index ${i} not found in indices`)
+            }
             const row = data[index]
             if (row === undefined) {
               throw new Error('Row not fetched')
             }
             const { cells } = row
-            wrapped[i - start].index.resolve(index)
+            const wrappedRow = wrapped[i - start]
+            if (wrappedRow === undefined) {
+              throw new Error(`Wrapped row missing at index ${i - start}`)
+            }
+            wrappedRow.index.resolve(index)
             for (const key of header) {
-              if (key in cells) {
+              const cell = cells[key]
+              if (cell) {
                 // TODO(SL): should we remove this check? It makes sense only if header change
                 // but if so, I guess we will have more issues
-                cells[key]
+                cell
                   .then((value: unknown) => {
-                    wrapped[i - start]?.cells[key].resolve(value)
+                    const wrappedCell = wrappedRow.cells[key]
+                    if (wrappedCell === undefined) {
+                      throw new Error(`Wrapped cell not found for column ${key}`)
+                    }
+                    wrappedCell.resolve(value)
                   })
                   .catch((error: unknown) => {
                     console.error('Error resolving sorted row', error)
@@ -98,8 +123,12 @@ export function parquetDataFrame(from: AsyncBufferFrom, metadata: FileMetaData):
         return wrapped
       } else {
         for (let i = 0; i < groups.length; i++) {
-          const groupStart = groupEnds[i - 1] || 0
-          if (start < groupEnds[i] && end > groupStart) {
+          const groupStart = groupEnds[i - 1] ?? 0
+          const groupEnd = groupEnds[i]
+          if (groupEnd === undefined) {
+            throw new Error(`Missing group end at index ${i}`)
+          }
+          if (start < groupEnd && end > groupStart) {
             fetchRowGroup(i)
           }
         }

src/lib/utils.ts

@@ -63,11 +63,15 @@ export function formatFileSize(bytes: number): string {
   if (bytes === 0) return '0 b'
   const i = Math.floor(Math.log2(bytes) / 10)
   if (i === 0) return bytes.toLocaleString('en-US') + ' b'
+  const size = sizes[i]
+  if (size === undefined) {
+    throw new Error(`Size not found at index ${i}`)
+  }
   const base = bytes / Math.pow(1024, i)
   return (
     (base < 10 ? base.toFixed(1) : Math.round(base)).toLocaleString('en-US') +
     ' ' +
-    sizes[i]
+    size
   )
 }
 

src/lib/workers/parquetWorker.ts

@@ -38,7 +38,7 @@ self.onmessage = async ({ data }: {
         throw new Error('sortIndex requires all rows')
       const sortColumn = await parquetQuery({ metadata, file, columns: [orderBy], compressors })
       const indices = Array.from(sortColumn, (_, index) => index).sort((a, b) =>
-        compare<unknown>(sortColumn[a][orderBy], sortColumn[b][orderBy])
+        compare<unknown>(sortColumn[a]?.[orderBy], sortColumn[b]?.[orderBy])
       )
       postIndicesMessage({ indices, queryId })
     } catch (error) {

tsconfig.json

@@ -16,6 +16,7 @@
     "noUnusedParameters": true,
     "noFallthroughCasesInSwitch": true,
     "noUncheckedSideEffectImports": true,
+    "noUncheckedIndexedAccess": true,
 
     "rootDir": "src",
     "outDir": "lib",