swiftlang/swift-package-manager

[SR-6548] SwiftPM's POSIX.chdir never works when binary is found via $PATH

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#4904 opened on Dec 6, 2017

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buggood first issue

Description
Previous ID SR-6548
Radar None
Original Reporter jaybuff (JIRA User)
Type Bug
Votes 0
Component/s Package Manager
Labels Bug, StarterBug
Assignee legendecas (JIRA)
Priority Medium

md5: 7f6b9fff863f8eada827047e65debf1f

Issue Description:

I'm using SwiftPM's Utility product and ran into an issue with chdir. To reproduce the program has to be found on the path:

swift package init --type executable

  1. add swiftpm dependency to Package.swift like this:
    .package(url: "https://github.com/apple/swift-package-manager.git", .exact("0.1.0"))

$ cat Sources/ChdirProg/main.swift
import POSIX
try chdir("/tmp")

swift build
export PATH=$PWD/.build/debug/:$PATH
ChdirProg
fatal error: Error raised at top level: realpath error: No such file or directory (2): ChdirProg: file /Library/Caches/com.apple.xbs/Sources/swiftlang/swiftlang-900.0.65.2/src/swift/stdlib/public/core/ErrorType.swift, line 187

This is because POSIX/chdir.swift calls realpath(CommandLine.arguments.first when the program name is resolved via $PATH.

I suspect this causes issues with --package-path, but am unsure how to cause this bug to manifest itself with swift build. Perhaps when swift build re-execs swift-build it always uses the full path?

Contributor guide

Tech stack
swift
Domain
toolingdeveloper experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Swift language basicsUnderstanding of POSIX realpath
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
The issue is caused by a call to realpath(CommandLine.arguments.first) in POSIX/chdir.swift. When the binary is invoked via $PATH, CommandLine.arguments.first is just the program name, not a full path, so realpath fails. To fix, you can check if the argument is already an absolute path or resolve it using the PATH environment variable. Look at the file Sources/POSIX/POSIX/chdir.swift. Also consider if the issue is still reproducible with the latest SwiftPM version. The discussion in the issue suggests a clear root cause, so implementing a fix should be straightforward.