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Fix some cases where AbsolutePath::relative(to: AbsolutePath) would assert on Windows #534

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Fix some cases where AbsolutePath::relative(to: AbsolutePath) would assert on Windows #534

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21 changes: 17 additions & 4 deletions Sources/TSCBasic/Path.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -515,13 +515,25 @@ private struct WindowsPath: Path, Sendable {
}

init(string: String) {
var path: String
if string.first?.isASCII ?? false, string.first?.isLetter ?? false, string.first?.isLowercase ?? false,
string.count > 1, string[string.index(string.startIndex, offsetBy: 1)] == ":"
{
self.string = "\(string.first!.uppercased())\(string.dropFirst(1))"
path = "\(string.first!.uppercased())\(string.dropFirst(1))"
} else {
self.string = string
path = string
}
// There seems to be many assumptions around paths and trailing '\'
var substring = path[path.startIndex..<path.endIndex]
while !substring.isEmpty && substring.utf8.last == UInt8(ascii: "\\") {
substring = substring.dropLast()
}
if !substring.isEmpty && substring.last != ":" {
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@compnerd compnerd Dec 10, 2025

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This is kinda sketchy. The last character being : could be a malformed path, e.g. C:\file.txt:.

// Drop the trailing '\', unless the string path only
// has '\', and unless the slashes are right after the drive letter.
path = String(substring)
}
self.string = path
}

private static func repr(_ path: String) -> String {
Expand Down Expand Up @@ -568,6 +580,7 @@ private struct WindowsPath: Path, Sendable {
_ = string.withCString(encodedAs: UTF16.self) { root in
name.withCString(encodedAs: UTF16.self) { path in
PathAllocCombine(root, path, ULONG(PATHCCH_ALLOW_LONG_PATHS.rawValue), &result)
_ = PathCchStripPrefix(result, wcslen(result))
}
}
defer { LocalFree(result) }
Expand All @@ -579,6 +592,7 @@ private struct WindowsPath: Path, Sendable {
_ = string.withCString(encodedAs: UTF16.self) { root in
relativePath.string.withCString(encodedAs: UTF16.self) { path in
PathAllocCombine(root, path, ULONG(PATHCCH_ALLOW_LONG_PATHS.rawValue), &result)
_ = PathCchStripPrefix(result, wcslen(result))
}
}
defer { LocalFree(result) }
Expand Down Expand Up @@ -965,8 +979,7 @@ extension AbsolutePath {
preconditionFailure("invalid relative path computed from \(pathString)")
}
}

assert(AbsolutePath(base, result) == self)
assert(AbsolutePath(base, result) == self, "\(AbsolutePath(base, result)) != \(self)")
return result
}

Expand Down