swiftlang/swift

[SR-4716] Better diagnostics for multifile executable without a main.swift file

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#47,293 opened on Apr 27, 2017

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 (5 comments) (0 reactions) (0 assignees)Swift (69,989 stars) (10,719 forks)batch import
compilerdiagnostics qualitygood first issueimprovementlegacy driver

Description
Previous ID SR-4716
Radar None
Original Reporter @huonw
Type Improvement
Status In Progress
Resolution
Votes 0
Component/s Compiler
Labels Improvement, DiagnosticsQoI, Driver, StarterBug
Assignee None
Priority Medium

md5: 107a386ff1ef4614f95e66bc776c43f4

Issue Description:

$ touch file1.swift file2.swift
$ swiftc file1.swift file2.swift
Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
<unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)

The problem here is neither file is called main.swift, so the top-level-code `main` function doesn't get emitted. The compiler should check the file names and emit an error rather than going all the way through compilation to hit the link error.

Contributor guide

Tech stack
swift
Domain
developer experiencetooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
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.
clear
Prerequisites
Swift compiler driver knowledgeFamiliarity with file name detection in compilation pipeline
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Investigate the Swift compiler driver code, specifically where it determines whether to emit the top level code entry point. The issue suggests adding a check for file names (e.g., main.swift) before the linking step to emit a clear diagnostic. Look for the driver's handling of multiple source files and the condition that checks for a main.swift file. The fix likely involves modifying the driver to produce an error when no main.swift is present among the input files.