[brandan-prnd]

Summary

ReplacementModuleName embeds the source file's base name in the thunk module name ({Module}_PreviewReplacement_{FileName}_{N}). A file name containing characters that are not valid in a Swift identifier (., +, -, spaces, …) makes that an invalid module name, and swiftc rejects the thunk before compiling anything.

This PR replaces every character outside [A-Za-z0-9_] with _, so previews work regardless of what characters a project uses in its file names.

Problem

A module name has to be a valid Swift identifier, but axe users are free to put other characters in their file names. Whatever the convention, the thunk then fails before anything is compiled:

module name "App_PreviewReplacement_FooView.ui_0" is not a valid identifier

Two examples we hit:

• Foo+Bar.swift — the common Swift name for an extension file (String+Validation.swift, …).
• FooView.ui.swift — a project-specific convention in our codebase. We suffix UI component files with .ui so that AI coding tools can tell a UI component from other Swift files by name alone (e.g. to pick capture targets). It is not a general Swift convention, but it is a legal file name, and . is exactly the kind of character this code should tolerate.

The source itself is never parsed; the failure is purely in the -module-name argument.

Fix

var nonIdentifierRe = regexp.MustCompile(`[^A-Za-z0-9_]`)

func ReplacementModuleName(moduleName, sourceFileName string, counter int) string {
    base := strings.TrimSuffix(filepath.Base(sourceFileName), filepath.Ext(sourceFileName))
    // "Foo+Bar.swift" or "FooView.ui.swift" would otherwise yield an invalid module identifier.
    base = nonIdentifierRe.ReplaceAllString(base, "_")
    return fmt.Sprintf("%s_PreviewReplacement_%s_%d", moduleName, base, counter)
}

Notes on the choice:

• Foo+Bar.swift and Foo_Bar.swift map to the same base, but the trailing counter is the per-session reload counter (also used for thunk_<N>.dylib), so two files never share a module name within one host process. This is the same property the existing code already relied on for files with identical base names in different directories.
• The module name is internal and only shows up in logs; it does not affect what is captured.
• Non-ASCII letters are replaced too. swiftc does accept Unicode module names, so [^\p{L}\p{N}_] would preserve them, but I kept the conservative ASCII set since Go's \p{L} and Swift's identifier grammar are not guaranteed to agree. Happy to switch if you prefer readable non-ASCII names.

Verification

• TestReplacementModuleName now covers FooView.ui.swift → FooView_ui and Foo+Bar.swift → Foo_Bar.
• Verified end to end: a *.ui.swift file that previously failed with the error above now captures.

[k-kohey]

Thanks for your contribution!