Prevent panic when decoding string named types

[shuheiktgw]

Closes #741

Previously, decoding string named type fields returned the converted string values directly, which could lead to a panic if the types didn’t match. This update adds a type check and performs the conversion if the types do not match.

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• Describe the purpose for which you created this PR.
• Create test code that corresponds to the modification

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.85%. Comparing base (04f9bb5) to head (74d87cd).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #743      +/-   ##
==========================================
+ Coverage   77.83%   77.85%   +0.02%     
==========================================
  Files          22       22              
  Lines        8056     8064       +8     
==========================================
+ Hits         6270     6278       +8     
  Misses       1370     1370              
  Partials      416      416              

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[Copilot]

Pull Request Overview

Adds support for decoding YAML values into string-alias types without panicking, along with corresponding tests.

• Introduce TestString alias and new test cases for mapping both unquoted and numeric YAML values into TestString.
• Refactor convertValue to collect primitive values into a strVal before converting to the target type, then special-case named string types.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
decode_test.go	Adds TestString alias and table-driven tests for mapping YAML values into TestString.
decode.go	Refactors convertValue to accumulate a string buffer, then convert to alias string types.

Comments suppressed due to low confidence (2)

decode.go:637

• This condition will return early for non-string kinds (e.g. int) when targeting a string alias, causing a panic instead of going through the intended numeric-to-string conversion path. Consider changing to v.Type().Kind() == reflect.String or removing this early return so that numeric and boolean kinds hit the switch and get formatted into strings first.

if typ.Kind() == reflect.String && v.Type().Kind() != reflect.String {

decode_test.go:40

• Tests cover string and numeric inputs for TestString, but boolean and float values for the alias are not verified. Adding cases like source: "v: true\n", value: map[string]TestString{"v": "true"} and a float test will ensure full coverage of all primitive-to-string conversions.

{

[goccy]

Thank you for your great PR ! LGTM