From 97ba0c80e081b8b64670cc2f8a914bc8c6e1896f Mon Sep 17 00:00:00 2001
From: Steven Wu <stevenwu@apple.com>
Date: Tue, 14 Oct 2025 16:28:47 -0700
Subject: [PATCH] [System] Use a larger limit for when to use response file

Drop the baseline number used by `xarg` when determining if a response
file is needed when generating command. macOS on apple silicon actually
has a really large limit when it comes to command-line limit and less
response file means faster build and build logs easier to read.
---
 Sources/SwiftDriver/Utilities/System.swift    | 10 ++++------
 Tests/SwiftDriverTests/SwiftDriverTests.swift |  4 ++--
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/Sources/SwiftDriver/Utilities/System.swift b/Sources/SwiftDriver/Utilities/System.swift
index 8c25e831e..f39157e38 100644
--- a/Sources/SwiftDriver/Utilities/System.swift
+++ b/Sources/SwiftDriver/Utilities/System.swift
@@ -62,17 +62,15 @@ func quoteArgument(_ argument: String) -> String {
 #if canImport(Darwin) || os(Linux) || os(Android) || os(OpenBSD) || os(FreeBSD)
 // Adapted from llvm::sys::commandLineFitsWithinSystemLimits.
 func commandLineFitsWithinSystemLimits(path: String, args: [String]) -> Bool {
-  let upperBound = sysconf(Int32(_SC_ARG_MAX))
-  guard upperBound != -1 else {
+  let systemLimit = sysconf(Int32(_SC_ARG_MAX))
+  guard systemLimit != -1 else {
     // The system reports no limit.
     return true
   }
   // The lower bound for ARG_MAX on a POSIX system
-  let lowerBound = Int(_POSIX_ARG_MAX)
-  // This the same baseline used by xargs.
-  let baseline = 128 * 1024
+  let posixLimit = Int(_POSIX_ARG_MAX)
 
-  var effectiveArgMax = max(min(baseline, upperBound), lowerBound)
+  var effectiveArgMax = max(systemLimit, posixLimit)
   // Conservatively assume environment variables consume half the space.
   effectiveArgMax /= 2
 
diff --git a/Tests/SwiftDriverTests/SwiftDriverTests.swift b/Tests/SwiftDriverTests/SwiftDriverTests.swift
index fba975677..10a35eab0 100644
--- a/Tests/SwiftDriverTests/SwiftDriverTests.swift
+++ b/Tests/SwiftDriverTests/SwiftDriverTests.swift
@@ -1766,7 +1766,7 @@ final class SwiftDriverTests: XCTestCase {
   }
 
   func testUsingResponseFiles() throws {
-    let manyArgs = (1...20000).map { "-DTEST_\($0)" }
+    let manyArgs = (1...200000).map { "-DTEST_\($0)" }
     // Needs response file
     do {
       let source = try AbsolutePath(validating: "/foo.swift")
@@ -1879,7 +1879,7 @@ final class SwiftDriverTests: XCTestCase {
     // The jobs below often take large command lines (e.g., when passing a large number of Clang
     // modules to Swift). Ensure that they don't regress in their ability to pass response files
     // from the driver to the frontend.
-    let manyArgs = (1...20000).map { "-DTEST_\($0)" }
+    let manyArgs = (1...200000).map { "-DTEST_\($0)" }
 
     // Compile + separate emit module job
     do {