[shibayan]

Summary

Closes #410.

#403 and #417 already covered part of this issue:

• one snapshot of Items for rendering and the result
• DefaultValues outside Items are ignored
• Ctrl+A / Ctrl+I that would exceed Maximum are rejected as a whole
• empty lists no longer divide by zero

This PR covers the remaining boundary conditions and documents the rules.

Changes

• Duplicate items (Select and MultiSelect): equal items (EqualityComparer<T>.Default) are listed once, at the position of the first.

  • Before, checking one of several equal items in MultiSelect checked all of them, and the result returned each one. With Items = ["a", "a"] and Maximum = 1, Enter returned two items, and Minimum counted distinct items while the result did not.

• Options that make the prompt unanswerable now throw before it is shown:

  Options	Exception	Before
  Select with no items	ArgumentException (Items)	Shown, but Enter was always rejected
  MultiSelect with Minimum > item count (after duplicates are removed)	ArgumentOutOfRangeException (Minimum)	Shown, but Enter was always rejected

  With these options, the only way out was to cancel. When ThrowExceptionOnCancel is false, canceling calls Environment.Exit(1). An empty MultiSelect with Minimum = 0 still works.

• Validation before the driver is created: options are validated and Items is snapshotted in a static Prepare that runs before the base constructor creates the console driver. Before, invalid options (for example, a negative Minimum) threw after the driver was created, and the driver was never disposed.

• Japanese message fix: Validation_Minimum_OutOfRange referenced {1} with a single argument. In the ja culture, a negative Minimum threw FormatException instead of ArgumentOutOfRangeException.

• New messages: for the two new exceptions, in en, ja, de-DE, and zh-Hans.

• Docs (en/ja):

  • Select: "Item Rules" (snapshot and duplicates, DefaultValue, Enter and filter selection, empty items).
  • MultiSelect: "Selection Rules", with a table of how Minimum and Maximum apply to Space, Ctrl+A / Ctrl+I, DefaultValues, and Enter.

Compatibility

• Reversed from Fix runtime bugs in Select, MultiSelect, Input and DefaultConsoleDriver #417: an empty Select no longer renders and waits for cancel; it throws ArgumentException. The test that pinned the old behavior is replaced.
• Kept from Fix runtime bugs in Select, MultiSelect, Input and DefaultConsoleDriver #417: more DefaultValues than Maximum still start checked, and Enter is rejected until enough are unchecked. The prompt can still be answered, so the rule is to throw only when it cannot be answered.
• Code that passed duplicate items now sees each value once.

Testing

• New FormInteractionTests:
  • empty Select and Minimum > items, including duplicates and empty Items, throw without creating the console driver
  • invalid options also throw without creating the console driver
  • limit errors format correctly in ja-JP, de-DE, and zh-Hans
  • duplicates in Select, MultiSelect, and Ctrl+A with Maximum = 1
• All 11 new cases fail on master.
• dotnet build, dotnet test (1246 passed), and dotnet format --verify-no-changes
• Native AOT verification (net10.0, win-x64): 65/65
• VitePress docs build

🤖 Generated with Claude Code

[Copilot]

🟢 Approval recommended

Static review found no blocking issues; the remaining documentation clarification is nonblocking.

1 open issue

• Clarify automatic selection when DefaultValue is unmatched · New

1 file not reviewed

• src/Sharprompt/Strings/Resource.Designer.cs: Generated file

What changed in this PR

Makes Select and MultiSelect boundary behavior consistent and documents compatibility changes.

Changes:

• Deduplicates items and rejects unanswerable options before creating the console driver.
• Adds localized validation messages and fixes Japanese error formatting.
• Adds regression tests and English/Japanese selection rules.

File	Description
tests/​Sharprompt.Tests/​Forms/​FormInteractionTests.cs	Tests duplicates, validation timing, and localized errors.
src/​Sharprompt/​Strings/​Resource.zh-Hans.resx	Adds Chinese validation messages.
src/​Sharprompt/​Strings/​Resource.resx	Adds default validation messages.
src/​Sharprompt/​Strings/​Resource.ja.resx	Adds Japanese messages and fixes a placeholder.
src/​Sharprompt/​Strings/​Resource.Designer.cs	Exposes new resource strings.
src/​Sharprompt/​Strings/​Resource.de-DE.resx	Adds German validation messages.
src/​Sharprompt/​Forms/​SelectForm.cs	Deduplicates items and validates before driver creation.
src/​Sharprompt/​Forms/​MultiSelectForm.cs	Deduplicates items and rejects impossible minimums early.
docs/​ja/​prompt-types/​select.md	Documents Select rules in Japanese.
docs/​ja/​prompt-types/​multi-select.md	Documents MultiSelect rules in Japanese.
docs/​en/​prompt-types/​select.md	Documents Select rules in English.
docs/​en/​prompt-types/​multi-select.md	Documents MultiSelect rules in English.

_{Review effort: Balanced}

[Copilot]

🟢 Approval recommended

No unresolved issues were identified, and the implementation, regression coverage, and documentation consistently address the intended boundary conditions.

No open issues 🎉

1 resolved since last review

• Clarify automatic selection when DefaultValue is unmatched

1 file not reviewed

• src/Sharprompt/Strings/Resource.Designer.cs: Generated file

_{Review effort: Balanced}