perf: improve empty object checks

Author: johannschopplich

packages/toon/src/decode/decoders.ts

@@ -73,7 +73,8 @@ function decodeObject(cursor: LineCursor, baseDepth: Depth, options: ResolvedDec
     }
 
     if (line.depth === computedDepth) {
-      const [key, value, isQuoted] = decodeKeyValuePair(line, cursor, computedDepth, options)
+      cursor.advance()
+      const { key, value, isQuoted } = decodeKeyValue(line.content, cursor, computedDepth, options)
       obj[key] = value
 
       // Track quoted dotted keys for expansion phase
@@ -134,17 +135,6 @@ function decodeKeyValue(
   return { key, value: decodedValue, followDepth: baseDepth + 1, isQuoted }
 }
 
-function decodeKeyValuePair(
-  line: ParsedLine,
-  cursor: LineCursor,
-  baseDepth: Depth,
-  options: ResolvedDecodeOptions,
-): [key: string, value: JsonValue, isQuoted: boolean] {
-  cursor.advance()
-  const { key, value, isQuoted } = decodeKeyValue(line.content, cursor, baseDepth, options)
-  return [key, value, isQuoted]
-}
-
 // #endregion
 
 // #region Array decoding
@@ -396,7 +386,8 @@ function decodeObjectFromListItem(
     }
 
     if (line.depth === followDepth && !line.content.startsWith(LIST_ITEM_PREFIX)) {
-      const [k, v, kIsQuoted] = decodeKeyValuePair(line, cursor, followDepth, options)
+      cursor.advance()
+      const { key: k, value: v, isQuoted: kIsQuoted } = decodeKeyValue(line.content, cursor, followDepth, options)
       obj[k] = v
 
       // Track quoted dotted keys

packages/toon/src/decode/expand.ts

@@ -52,13 +52,11 @@ export function expandPathsSafe(value: JsonValue, strict: boolean): JsonValue {
 
   if (isJsonObject(value)) {
     const expandedObject: JsonObject = {}
-    const keys = Object.keys(value)
 
     // Check if this object has quoted key metadata
     const quotedKeys = (value as ObjectWithQuotedKeys)[QUOTED_KEY_MARKER]
 
-    for (const key of keys) {
-      const keyValue = value[key]!
+    for (const [key, keyValue] of Object.entries(value)) {
 
       // Skip expansion for keys that were originally quoted
       const isQuoted = quotedKeys?.has(key)
@@ -207,8 +205,7 @@ function mergeObjects(
   source: JsonObject,
   strict: boolean,
 ): void {
-  for (const key of Object.keys(source)) {
-    const sourceValue = source[key]!
+  for (const [key, sourceValue] of Object.entries(source)) {
     const targetValue = target[key]
 
     if (targetValue === undefined) {

packages/toon/src/decode/parser.ts

@@ -302,12 +302,11 @@ export function parseQuotedKey(content: string, start: number): { key: string, e
 }
 
 export function parseKeyToken(content: string, start: number): { key: string, end: number, isQuoted: boolean } {
-  if (content[start] === DOUBLE_QUOTE) {
-    return { ...parseQuotedKey(content, start), isQuoted: true }
-  }
-  else {
-    return { ...parseUnquotedKey(content, start), isQuoted: false }
-  }
+  const isQuoted = content[start] === DOUBLE_QUOTE
+  const result = isQuoted
+    ? parseQuotedKey(content, start)
+    : parseUnquotedKey(content, start)
+  return { ...result, isQuoted }
 }
 
 // #endregion

packages/toon/src/decode/scanner.ts

@@ -47,17 +47,7 @@ export class LineCursor {
 
   peekAtDepth(targetDepth: Depth): ParsedLine | undefined {
     const line = this.peek()
-    if (!line || line.depth < targetDepth) {
-      return undefined
-    }
-    if (line.depth === targetDepth) {
-      return line
-    }
-    return undefined
-  }
-
-  hasMoreAtDepth(targetDepth: Depth): boolean {
-    return this.peekAtDepth(targetDepth) !== undefined
+    return line?.depth === targetDepth ? line : undefined
   }
 }
 

packages/toon/src/decode/validation.ts

@@ -24,11 +24,8 @@ export function validateNoExtraListItems(
   itemDepth: Depth,
   expectedCount: number,
 ): void {
-  if (cursor.atEnd())
-    return
-
   const nextLine = cursor.peek()
-  if (nextLine && nextLine.depth === itemDepth && nextLine.content.startsWith(LIST_ITEM_PREFIX)) {
+  if (nextLine?.depth === itemDepth && nextLine.content.startsWith(LIST_ITEM_PREFIX)) {
     throw new RangeError(`Expected ${expectedCount} list array items, but found more`)
   }
 }
@@ -41,13 +38,9 @@ export function validateNoExtraTabularRows(
   rowDepth: Depth,
   header: ArrayHeaderInfo,
 ): void {
-  if (cursor.atEnd())
-    return
-
   const nextLine = cursor.peek()
   if (
-    nextLine
-    && nextLine.depth === rowDepth
+    nextLine?.depth === rowDepth
     && !nextLine.content.startsWith(LIST_ITEM_PREFIX)
     && isDataRow(nextLine.content, header.delimiter)
   ) {
@@ -71,14 +64,13 @@ export function validateNoBlankLinesInRange(
   // Find blank lines within the range
   // Note: We don't filter by depth because ANY blank line between array items is an error,
   // regardless of its indentation level
-  const blanksInRange = blankLines.filter(
-    blank => blank.lineNumber > startLine
-      && blank.lineNumber < endLine,
+  const firstBlank = blankLines.find(
+    blank => blank.lineNumber > startLine && blank.lineNumber < endLine,
   )
 
-  if (blanksInRange.length > 0) {
+  if (firstBlank) {
     throw new SyntaxError(
-      `Line ${blanksInRange[0]!.lineNumber}: Blank lines inside ${context} are not allowed in strict mode`,
+      `Line ${firstBlank.lineNumber}: Blank lines inside ${context} are not allowed in strict mode`,
     )
   }
 }

packages/toon/src/encode/encoders.ts

@@ -1,7 +1,7 @@
 import type { Depth, JsonArray, JsonObject, JsonPrimitive, JsonValue, ResolvedEncodeOptions } from '../types'
 import { DOT, LIST_ITEM_MARKER } from '../constants'
 import { tryFoldKeyChain } from './folding'
-import { isArrayOfArrays, isArrayOfObjects, isArrayOfPrimitives, isJsonArray, isJsonObject, isJsonPrimitive } from './normalize'
+import { isArrayOfArrays, isArrayOfObjects, isArrayOfPrimitives, isEmptyObject, isJsonArray, isJsonObject, isJsonPrimitive } from './normalize'
 import { encodeAndJoinPrimitives, encodeKey, encodePrimitive, formatHeader } from './primitives'
 import { LineWriter } from './writer'
 
@@ -38,8 +38,8 @@ export function encodeObject(value: JsonObject, writer: LineWriter, depth: Depth
 
   const effectiveFlattenDepth = remainingDepth ?? options.flattenDepth
 
-  for (const key of keys) {
-    encodeKeyValuePair(key, value[key]!, writer, depth, options, keys, rootLiteralKeys, pathPrefix, effectiveFlattenDepth)
+  for (const [key, val] of Object.entries(value)) {
+    encodeKeyValuePair(key, val, writer, depth, options, keys, rootLiteralKeys, pathPrefix, effectiveFlattenDepth)
   }
 }
 
@@ -66,7 +66,7 @@ export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWr
           encodeArray(foldedKey, leafValue, writer, depth, options)
           return
         }
-        else if (isJsonObject(leafValue) && Object.keys(leafValue).length === 0) {
+        else if (isJsonObject(leafValue) && isEmptyObject(leafValue)) {
           writer.push(depth, `${encodedFoldedKey}:`)
           return
         }
@@ -94,13 +94,8 @@ export function encodeKeyValuePair(key: string, value: JsonValue, writer: LineWr
     encodeArray(key, value, writer, depth, options)
   }
   else if (isJsonObject(value)) {
-    const nestedKeys = Object.keys(value)
-    if (nestedKeys.length === 0) {
-      // Empty object
-      writer.push(depth, `${encodedKey}:`)
-    }
-    else {
-      writer.push(depth, `${encodedKey}:`)
+    writer.push(depth, `${encodedKey}:`)
+    if (!isEmptyObject(value)) {
       encodeObject(value, writer, depth + 1, options, rootLiteralKeys, currentPath, effectiveFlattenDepth)
     }
   }
@@ -279,16 +274,14 @@ export function encodeMixedArrayAsListItems(
 }
 
 export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, depth: Depth, options: ResolvedEncodeOptions): void {
-  const keys = Object.keys(obj)
-  if (keys.length === 0) {
+  if (isEmptyObject(obj)) {
     writer.push(depth, LIST_ITEM_MARKER)
     return
   }
 
-  // First key-value on the same line as "- "
-  const firstKey = keys[0]!
+  const entries = Object.entries(obj)
+  const [firstKey, firstValue] = entries[0]!
   const encodedKey = encodeKey(firstKey)
-  const firstValue = obj[firstKey]!
 
   if (isJsonPrimitive(firstValue)) {
     writer.pushListItem(depth, `${encodedKey}: ${encodePrimitive(firstValue, options.delimiter)}`)
@@ -327,20 +320,16 @@ export function encodeObjectAsListItem(obj: JsonObject, writer: LineWriter, dept
     }
   }
   else if (isJsonObject(firstValue)) {
-    const nestedKeys = Object.keys(firstValue)
-    if (nestedKeys.length === 0) {
-      writer.pushListItem(depth, `${encodedKey}:`)
-    }
-    else {
-      writer.pushListItem(depth, `${encodedKey}:`)
+    writer.pushListItem(depth, `${encodedKey}:`)
+    if (!isEmptyObject(firstValue)) {
       encodeObject(firstValue, writer, depth + 2, options)
     }
   }
 
-  // Remaining keys on indented lines
-  for (let i = 1; i < keys.length; i++) {
-    const key = keys[i]!
-    encodeKeyValuePair(key, obj[key]!, writer, depth + 1, options)
+  // Remaining entries on indented lines
+  for (let i = 1; i < entries.length; i++) {
+    const [key, value] = entries[i]!
+    encodeKeyValuePair(key, value, writer, depth + 1, options)
   }
 }
 

packages/toon/src/encode/folding.ts

@@ -1,7 +1,7 @@
 import type { JsonValue, ResolvedEncodeOptions } from '../types'
 import { DOT } from '../constants'
 import { isIdentifierSegment } from '../shared/validation'
-import { isJsonObject } from './normalize'
+import { isEmptyObject, isJsonObject } from './normalize'
 
 // #region Key folding helpers
 
@@ -160,25 +160,13 @@ function collectSingleKeyChain(
     currentValue = nextValue
   }
 
-  // Determine the tail - simplified with early returns
-  if (!isJsonObject(currentValue)) {
-    // Array, primitive, or null - this is a leaf value
+  // Determine the tail
+  if (!isJsonObject(currentValue) || isEmptyObject(currentValue)) {
+    // Array, primitive, null, or empty object - this is a leaf value
     return { segments, tail: undefined, leafValue: currentValue }
   }
 
-  const keys = Object.keys(currentValue)
-
-  if (keys.length === 0) {
-    // Empty object is a leaf
-    return { segments, tail: undefined, leafValue: currentValue }
-  }
-
-  if (keys.length === 1 && segments.length === maxDepth) {
-    // Hit depth limit with remaining chain
-    return { segments, tail: currentValue, leafValue: currentValue }
-  }
-
-  // Multi-key object is the remainder
+  // Has keys - return as tail (remainder)
   return { segments, tail: currentValue, leafValue: currentValue }
 }
 

packages/toon/src/encode/normalize.ts

@@ -94,6 +94,10 @@ export function isJsonObject(value: unknown): value is JsonObject {
   return value !== null && typeof value === 'object' && !Array.isArray(value)
 }
 
+export function isEmptyObject(value: JsonObject): boolean {
+  return Object.keys(value).length === 0
+}
+
 export function isPlainObject(value: unknown): value is Record<string, unknown> {
   if (value === null || typeof value !== 'object') {
     return false
@@ -108,15 +112,15 @@ export function isPlainObject(value: unknown): value is Record<string, unknown>
 // #region Array type detection
 
 export function isArrayOfPrimitives(value: JsonArray): value is readonly JsonPrimitive[] {
-  return value.every(item => isJsonPrimitive(item))
+  return value.length === 0 || value.every(item => isJsonPrimitive(item))
 }
 
 export function isArrayOfArrays(value: JsonArray): value is readonly JsonArray[] {
-  return value.every(item => isJsonArray(item))
+  return value.length === 0 || value.every(item => isJsonArray(item))
 }
 
 export function isArrayOfObjects(value: JsonArray): value is readonly JsonObject[] {
-  return value.every(item => isJsonObject(item))
+  return value.length === 0 || value.every(item => isJsonObject(item))
 }
 
 // #endregion

packages/toon/src/encode/primitives.ts

@@ -21,7 +21,7 @@ export function encodePrimitive(value: JsonPrimitive, delimiter?: string): strin
   return encodeStringLiteral(value, delimiter)
 }
 
-export function encodeStringLiteral(value: string, delimiter: string = COMMA): string {
+export function encodeStringLiteral(value: string, delimiter: string = DEFAULT_DELIMITER): string {
   if (isSafeUnquoted(value, delimiter)) {
     return value
   }
@@ -45,7 +45,7 @@ export function encodeKey(key: string): string {
 
 // #region Value joining
 
-export function encodeAndJoinPrimitives(values: readonly JsonPrimitive[], delimiter: string = COMMA): string {
+export function encodeAndJoinPrimitives(values: readonly JsonPrimitive[], delimiter: string = DEFAULT_DELIMITER): string {
   return values.map(v => encodePrimitive(v, delimiter)).join(delimiter)
 }
 

packages/toon/src/shared/validation.ts

@@ -1,4 +1,4 @@
-import { COMMA, LIST_ITEM_MARKER } from '../constants'
+import { DEFAULT_DELIMITER, LIST_ITEM_MARKER } from '../constants'
 import { isBooleanOrNullLiteral } from './literal-utils'
 
 /**
@@ -39,7 +39,7 @@ export function isIdentifierSegment(key: string): boolean {
  * - Contains the active delimiter
  * - Starts with a list marker (hyphen)
  */
-export function isSafeUnquoted(value: string, delimiter: string = COMMA): boolean {
+export function isSafeUnquoted(value: string, delimiter: string = DEFAULT_DELIMITER): boolean {
   if (!value) {
     return false
   }