Passing `-p .` explicitly is treated as "no path" and prompts, swallowing the next stdin line as the path

[matt-edmondson]

What's wrong

BaseVerb.PathString defaults to "." (Verbs/BaseVerb.cs:15). Each verb then checks if (PathString is "." or "") to decide whether to prompt for a path (Verbs/Deduplicate.cs:15, DryRun.cs:15, Scan.cs:15, Stats.cs:15). Because "." is both the default and the "not supplied" marker, an explicit -p . / --path . meaning "the current directory" can't be told apart from leaving the option out.

Failure scenario

These were run in a directory containing two identical files:

• Scan -p . </dev/null prints Enter the path to scan: No path provided. Aborting. and does nothing. Scan -p ./ finds the duplicate group as expected.
• echo y | Deduplicate -p . prints Enter the path to deduplicate: Deduplicating: <cwd>/y and then Directory not found: <cwd>/y. The y meant to confirm the deletion is read as the path. With different input piped in, the run could target a directory the user never meant.

Suggested fix

• Make PathString a string? that defaults to null.
• Prompt only when string.IsNullOrWhiteSpace(PathString).
• Reset it to null rather than "." after a run.

Open PR #143 (for #138) moves the PathString = "." reset into a finally in BaseVerb<T>.Run. That PR is related but doesn't fix this, so the sentinel change should build on it.

Acceptance criteria

• Scan -p . scans the current directory without prompting.
• Leaving out -p still prompts.

[matt-edmondson]

Triage

• Category: Bug
• Priority: Medium. An explicit -p . prompts for a path and reads the next stdin line as that path. When input is piped, as in echo y | Deduplicate -p ., the tool can end up working on a directory the user never named, and Deduplicate deletes files. The workaround -p ./ exists.
• Area / suggested assignee: BaseVerb.PathString and the path prompt in each verb (Verbs/*.cs). Owner: @matt-edmondson
• Duplicates / in progress: not a duplicate. It is related to open PR fix: ask for a new path each time a menu verb runs [patch] #143 (for In the interactive menu, a verb that exits early silently reuses the previous path instead of prompting again #138), which moves the PathString = "." reset into a finally. Build this on fix: ask for a new path each time a menu verb runs [patch] #143, or fold it into fix: ask for a new path each time a menu verb runs [patch] #143 before merging.
• Next step: make PathString a string? that defaults to null, prompt only when IsNullOrWhiteSpace, and reset it to null. Add tests that -p . doesn't prompt and that leaving out -p still does.

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