Merge pull request #2696 from abertelrud/SR-12613

[SR-12613] [ManifestLoader] Go back to using `-fileno` option for the separate JSON output

Author: abertelrud

Sources/PackageDescription/PackageDescription.swift

@@ -368,14 +368,20 @@ public final class Package {
     private func registerExitHandler() {
         // Add a custom exit handler to cause the package's JSON representation
         // to be dumped at exit, if requested.  Emitting it to a separate file
-        // keeps any of the manifest's stdout output from interfering with it.
+        // descriptor from stdout keeps any of the manifest's stdout output from
+        // interfering with it.
         //
         // FIXME: This doesn't belong here, but for now is the mechanism we use
         // to get the interpreter to dump the package when attempting to load a
         // manifest.
-        if let optIdx = CommandLine.arguments.firstIndex(of: "-json-output-file") {
-            let jsonOutputFilePath = CommandLine.arguments[optIdx + 1]
-            dumpPackageAtExit(self, to: jsonOutputFilePath)
+        //
+        // Warning:  The `-fileno` flag is a contract between PackageDescription
+        // and libSwiftPM, and since different versions of the two can be used
+        // together, it isn't safe to rename or remove it.
+        if let optIdx = CommandLine.arguments.firstIndex(of: "-fileno") {
+            if let jsonOutputFileDesc = Int32(CommandLine.arguments[optIdx + 1]) {
+                dumpPackageAtExit(self, to: jsonOutputFileDesc)
+            }
         }
     }
 }
@@ -621,14 +627,14 @@ func manifestToJSON(_ package: Package) -> String {
 }
 
 var errors: [String] = []
-private var dumpInfo: (package: Package, path: String)?
-private func dumpPackageAtExit(_ package: Package, to path: String) {
+private var dumpInfo: (package: Package, fileDesc: Int32)?
+private func dumpPackageAtExit(_ package: Package, to fileDesc: Int32) {
     func dump() {
         guard let dumpInfo = dumpInfo else { return }
-        guard let fd = fopen(dumpInfo.path, "w") else { return }
+        guard let fd = fdopen(dumpInfo.fileDesc, "w") else { return }
         fputs(manifestToJSON(dumpInfo.package), fd)
         fclose(fd)
     }
-    dumpInfo = (package, path)
+    dumpInfo = (package, fileDesc)
     atexit(dump)
 }

Sources/PackageLoading/ManifestLoader.swift

@@ -579,9 +579,12 @@ public final class ManifestLoader: ManifestLoaderProtocol {
                     return
                 }
 
-                // Pass the path of a file to which the JSON representation of the manifest will be written.
+                // Pass an open file descriptor of a file to which the JSON representation of the manifest will be written.
                 let jsonOutputFile = tmpDir.appending(component: "\(packageIdentity)-output.json")
-                cmd = [compiledManifestFile.pathString, "-json-output-file", jsonOutputFile.pathString]
+                guard let jsonOutputFileDesc = fopen(jsonOutputFile.pathString, "w") else {
+                    throw StringError("couldn't create the manifest's JSON output file")
+                }
+                cmd = [compiledManifestFile.pathString, "-fileno", "\(fileno(jsonOutputFileDesc))"]
 
               #if os(macOS)
                 // If enabled, use sandbox-exec on macOS. This provides some safety against
@@ -599,6 +602,7 @@ public final class ManifestLoader: ManifestLoaderProtocol {
 
                 // Run the compiled manifest.
                 let runResult = try Process.popen(arguments: cmd)
+                fclose(jsonOutputFileDesc)
                 let runOutput = try (runResult.utf8Output() + runResult.utf8stderrOutput()).spm_chuzzle()
                 if let runOutput = runOutput {
                     // Append the runtime output to any compiler output we've received.