FuzzILLifter: Limit line size to 300

Some of our infrastructure doesn't like it if we print too long single
lines, so limit it arbitrarily.
Let's hope the indentation level never reaches this length.

Bug: 433646300
Change-Id: I4cfc3234bbd4738558054731e98eb991b186bf7b
Reviewed-on: https://chrome-internal-review.googlesource.com/c/v8/fuzzilli/+/8449617
Reviewed-by: Michael Achenbach <[email protected]>
Reviewed-by: Carl Smith <[email protected]>
Commit-Queue: Matthias Liedtke <[email protected]>

Author: Liedtke

Sources/Fuzzilli/Lifting/FuzzILLifter.swift

@@ -1323,7 +1323,7 @@ public class FuzzILLifter: Lifter {
     }
 
     public func lift(_ code: Code) -> String {
-        var w = ScriptWriter()
+        var w = ScriptWriter(maxLineLength: 300)
 
         for instr in code {
             lift(instr, with: &w)

Sources/Fuzzilli/Lifting/ScriptWriter.swift

@@ -29,24 +29,55 @@ struct ScriptWriter {
     /// Whether to include line numbers in the output.
     private let includeLineNumbers: Bool
 
+    // Split lines after this length. Do not use this in combination with JavaScript as it might
+    // split line comments, string literals, ... across multiple lines which changes semantics.
+    private let maxLineLength: Int
+
     /// Current line, used when including line numbers in the output.
     public private(set) var currentLineNumber = 0
 
-    public init (stripComments: Bool = false, includeLineNumbers: Bool = false, indent: Int = 4, initialIndentionLevel: Int = 0) {
+    public init (stripComments: Bool = false, includeLineNumbers: Bool = false, indent: Int = 4, initialIndentionLevel: Int = 0, maxLineLength: Int = Int.max) {
         self.indent = String(repeating: " ", count: indent)
         self.currentIndention = String(repeating: " ", count: indent * initialIndentionLevel)
         self.stripComments = stripComments
         self.includeLineNumbers = includeLineNumbers
+        self.maxLineLength = maxLineLength
     }
 
-    /// Emit one line of code.
-    mutating func emit<S: StringProtocol>(_ line: S) {
-        assert(!line.contains("\n"))
+    private mutating func emitImpl<S: StringProtocol>(_ line: S) {
         currentLineNumber += 1
         if includeLineNumbers { code += "\(String(format: "%3i", currentLineNumber)). " }
         code += currentIndention + line + "\n"
     }
 
+    /// Emit one line of code.
+    mutating func emit<S: StringProtocol>(_ line: S) {
+        assert(maxLineLength > currentIndention.count)
+        let splitAt = maxLineLength - currentIndention.count
+        assert(!line.contains("\n"))
+        var line = line.prefix(line.count)
+        while line.count > splitAt {
+            var lineToPrint = line.prefix(splitAt + 1)
+            if let spaceIndex = lineToPrint.lastIndex(of: " "),
+                spaceIndex != lineToPrint.startIndex {
+                // Only print the line if it contains non-space characters trimming all trailing
+                // spaces.
+                lineToPrint = lineToPrint.prefix(upTo: spaceIndex)
+                if let lastChar = (lineToPrint.lastIndex { $0 != " " }) {
+                    emitImpl(line.prefix(through: lastChar))
+                }
+                line = line.suffix(from: line.index(after: spaceIndex))
+            } else {
+                emitImpl(line.prefix(splitAt))
+                line = line.suffix(line.count - splitAt)
+            }
+            line = line.suffix(from: line.firstIndex {$0 != " "} ?? line.endIndex)
+        }
+        if !line.isEmpty {
+            emitImpl(line)
+        }
+    }
+
     /// Emit a comment.
     mutating func emitComment(_ comment: String) {
         guard !stripComments else { return }

Tests/FuzzilliTests/ScriptWriterTest.swift

@@ -0,0 +1,84 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import XCTest
+@testable import Fuzzilli
+
+class ScriptWriterTest: XCTestCase {
+
+    func testLineSplitting() {
+        var w = ScriptWriter(indent: 2, initialIndentionLevel: 0, maxLineLength: 10)
+        w.emit("My name is Ozymandias, king of kings. Look on my works, ye Mighty, and despair!")
+        let expected = """
+        My name is
+        Ozymandias
+        , king of
+        kings.
+        Look on my
+        works, ye
+        Mighty,
+        and
+        despair!
+
+        """
+        XCTAssertEqual(expected, w.code)
+    }
+
+    func testLineSplittingWithIndentation() {
+        var w = ScriptWriter(indent: 2, initialIndentionLevel: 0, maxLineLength: 8)
+        w.emit("My name is Ozymandias,")
+        w.increaseIndentionLevel()
+        w.emit("king of kings.")
+        w.decreaseIndentionLevel()
+        w.emit("Look on my works, ye Mighty,")
+        w.increaseIndentionLevel()
+        w.emit("and despair!")
+        w.decreaseIndentionLevel()
+        let expected = """
+        My name
+        is
+        Ozymandi
+        as,
+          king
+          of
+          kings.
+        Look on
+        my
+        works,
+        ye
+        Mighty,
+          and
+          despai
+          r!
+
+        """
+        XCTAssertEqual(expected, w.code)
+    }
+
+    func testLineSplittingMultiSpace() {
+      var w = ScriptWriter(indent: 2, initialIndentionLevel: 0, maxLineLength: 8)
+      let str = (0...10).map {"\($0)\(String(repeating: " ", count: $0))"}.joined()
+      w.emit(str)
+      let expected = """
+      01 2  3
+      4    5
+      6      7
+      8
+      9
+      10
+
+      """
+      XCTAssertEqual(expected, w.code)
+    }
+}