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A scheme or workspace with a control character in a value is written as malformed XML, and XcodeProj can't read it back

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
85/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
swift
Área
tooling

Línea de trabajo

Empieza con Sources/XcodeProj/Extensions/AEXML+XcodeFormat.swift y el escape de atributos y valores de cadena en xmlXcodeFormat. El issue describe pruebas en Tests/XcodeProjTests/Extensions/XcodeFormatForbiddenCharacterTests.swift; úsalas para comprobar los controles prohibidos, los controles válidos y los round-trips de scheme/workspace. El trabajo estará terminado cuando el XML escrito siga siendo legible y toda la suite de pruebas swift test pase.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

Context 🕵️‍♀️

XCScheme.write(path:override:), XCWorkspaceData.write(path:override:) and their dataRepresentation() render
through AEXMLDocument.xmlXcodeFormat (Sources/XcodeProj/Extensions/AEXML+XcodeFormat.swift). It escapes every
attribute value with AEXML's String.xmlEscaped, which handles &, <, >, ', ", \n, \r and \t. XML 1.0
also forbids, outright, the other C0 controls (U+0001–U+0008, U+000B, U+000C, U+000E–U+001F) and U+FFFE and U+FFFF.
No escape can write them; &#27; is malformed too. xmlEscaped copies them through, so the file XcodeProj writes is
not well-formed, and XCScheme(path:) / XCWorkspaceData(path:) throw on it.

The values come from callers: an environment variable's value, a pre- or post-action's scriptText, a command-line
argument, a file reference's path. Tools that generate schemes from a manifest pass such strings straight through.
#530 is an XcodeGen pre-action script that reached this writer. A terminal colour code pasted into a value, with a
raw ESC (U+001B), is the likeliest way in.

What 🌱

import PathKit
import XcodeProj

let launch = XCScheme.LaunchAction(
    runnable: nil,
    buildConfiguration: "Debug",
    environmentVariables: [XCScheme.EnvironmentVariable(variable: "PROMPT", value: "\u{1B}[31m$ \u{1B}[0m", enabled: true)]
)
let path = Path("App.xcscheme")
try XCScheme(name: "App", lastUpgradeVersion: "2600", version: "1.7", launchAction: launch).write(path: path, override: true)
_ = try XCScheme(path: path)
// throws: Error Domain=NSXMLParserErrorDomain Code=9 "(null)"
//   UserInfo={NSXMLParserErrorLineNumber=18, NSXMLParserErrorColumn=22, NSXMLParserErrorMessage=invalid character in attribute value}

Line 18 of App.xcscheme, through cat -v: value = "^[[31m$ ^[[0m". A workspace does the same: a FileRef at
.group("a\u{1}b.swift") is written as location = "group:a^Ab.swift", and XCWorkspaceData(path:) throws code 9
at line 5. With "red $ " and "ab.swift" instead, both files read back. Every one of the 30 code points fails the
same way.

Proposal 🎉

Replace each of those characters with U+FFFD in xmlXcodeFormat, after xmlEscaped:

--- a/Sources/XcodeProj/Extensions/AEXML+XcodeFormat.swift
+++ b/Sources/XcodeProj/Extensions/AEXML+XcodeFormat.swift
@@ -124,7 +124,7 @@ extension AEXMLElement {
         func print(key: String, value: String) {
             xml += "\n"
             xml += indent(withDepth: parentsCount)
-            xml += "\(key) = \"\(value.xmlEscaped)\""
+            xml += "\(key) = \"\(value.xcodeFormatEscaped)\""
         }
 
         if !attributes.isEmpty {
@@ -156,7 +156,7 @@ extension AEXMLElement {
                 // insert string value and close element
                 xml += ">\n"
                 xml += indent(withDepth: parentsCount - 1)
-                xml += ">\n\(string.xmlEscaped)"
+                xml += ">\n\(string.xcodeFormatEscaped)"
             }
         }
 
@@ -190,3 +190,21 @@ extension AEXMLElement {
         return indent
     }
 }
+
+extension String {
+    /// `xmlEscaped`, with U+FFFD in place of each character XML 1.0 cannot hold at all, even as a reference:
+    /// a C0 control other than tab, line feed and carriage return, U+FFFE or U+FFFF. A file holding one is not
+    /// well-formed, so neither XcodeProj nor any other XML reader can load it.
+    fileprivate var xcodeFormatEscaped: String {
+        var scalars = String.UnicodeScalarView()
+        for scalar in xmlEscaped.unicodeScalars {
+            switch scalar {
+            case "\u{0}"..."\u{8}", "\u{B}", "\u{C}", "\u{E}"..."\u{1F}", "\u{FFFE}", "\u{FFFF}":
+                scalars.append("\u{FFFD}")
+            default:
+                scalars.append(scalar)
+            }
+        }
+        return String(scalars)
+    }
+}

This loses the character, but the file stays loadable. The alternative is to throw from write and
dataRepresentation, which would mean xmlXcodeFormat throwing too. Output without these characters is unchanged.

I have an XCTest file, Tests/XcodeProjTests/Extensions/XcodeFormatForbiddenCharacterTests.swift, with four tests:
the scheme and the workspace above, all 30 code points in an attribute value, and a control (&, <, >, quotes,
tab and newline, which round-trip today). On main the three tests fail (32 assertions) and the control passes.
With the patch all four pass, and so does the full swift test: 387 XCTest and 95 Swift Testing tests. Happy to
open a PR with both.

AEXML's own xml output has the same gap in String.xmlEscaped (4.7.3, unchanged on its master). I have not
reported it there.

Environment. XcodeProj main at 948280a (AEXML 4.7.3). Xcode 27.2 (Swift 6.4.2), macOS 27.2, arm64.

Found while checking whether XML written by Swift packages parses.

Lenguaje dominante
Swift
Estrellas
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Forks
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Merge medio
5 h 54 min
PR fusionados (30 d)
8

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