[mkarimdev]

fix: resolve default value and placeholder collision in InputForm (#192)

Fixes #192

Summary

InputForm<T> rendered DefaultValue and Placeholder independently, so configuring both produced two adjacent hints with no separator and the same Hint color:

? Pick a color: (blue) ▏type a color

The placeholder looked like editable text following the default, and it was unclear which value Enter would submit.

This change makes the two hints mutually exclusive: while a default value is active, the default hint wins and the placeholder is not drawn. The placeholder is revealed only after the default is dismissed.

Behavior

State	Rendered	Enter returns
DefaultValue = "blue", Placeholder = "type a color"	? Pick a color: (blue) ▏	"blue"
Same, after [Backspace] on the empty buffer	? Pick a color: ▏type a color	null (string) / validation error (non-nullable)
Placeholder only	? Pick a color: ▏type a color	As before
DefaultValue only	? Pick a color: (blue) ▏	"blue"

No public API changes. The placeholder remains non-submittable, and DefaultValue remains the value used by Enter/Tab.

Before / After

Before — both hints drawn, no separation:

? Pick a color: (blue) ▏type a color

After — default suppresses the placeholder:

? Pick a color: (blue) ▏

After — [Backspace] dismisses the default and reveals the placeholder:

? Pick a color: ▏type a color

Implementation

src/Sharprompt/Forms/InputForm.cs — the placeholder branch in InputTemplate() becomes an else if of the default-value branch:

if (!string.IsNullOrEmpty(defaultValueText))
{
    offscreenBuffer.WriteHint($"({defaultValueText}) ");
}
else if (InputBuffer.Length == 0 && !string.IsNullOrEmpty(_options.Placeholder))
{
    offscreenBuffer.PushCursor();
    offscreenBuffer.WriteHint(_options.Placeholder);
}

This relies on the existing HandleBackspace() behavior, which already clears _defaultValue when Backspace is pressed on an empty buffer.

Tests

Added three tests in tests/Sharprompt.Tests/Forms/FormInteractionTests.cs:

• InputForm_DefaultValueAndPlaceholder_RendersDefaultOnly — asserts (blue) is rendered and the placeholder is absent.
• InputForm_BackspaceDismissesDefaultValue_RevealsPlaceholder — asserts the post-backspace frame contains the placeholder and no longer the default.
• InputForm_EmptyInputWithDefaultValueAndPlaceholder_ReturnsDefaultValue — asserts Enter on an empty buffer resolves to the default value.

Verification

dotnet build -c Release
dotnet test --project tests/Sharprompt.Tests/Sharprompt.Tests.csproj -c Release -f net10.0 --no-build
# 469 passed, 0 failed

dotnet test --project tests/Sharprompt.SourceGenerator.Tests/Sharprompt.SourceGenerator.Tests.csproj -c Release -f net10.0 --no-build
# 210 passed, 0 failed

dotnet format --verify-no-changes reports no formatting changes. Both net8.0 and net10.0 targets build successfully.

Compatibility

• No public API or option-surface changes.
• Existing default-value rendering tests are unaffected.
• Prompts without a DefaultValue behave exactly as before.