Android/Termux: etc fails to compile because `getpwent` declarations are unavailable

从 extconf.rb 的 getpwent 检测以及 etc.c 中的 setpwent/getpwent 调用开始。在 Android/Termux 上使用 gem install etc --no-document 重现失败，然后验证功能检测是否与配置的 Android API 可用的声明相匹配。完成标准是 gem 能够成功编译，或仅禁用受影响的功能。

My environment

• OS: Android/Termux
• arch: aarch64
• ruby: 4.0.6
• ruby gems version: 4.0.16
• gem version: etc 1.4.6
• compiler used: clang 21.1.8
• android api: 36

Description

Installing the etc gem is fails while compiling the native extension:

  gem install etc

The configuration step reports that getpwent() is available in the output:

  checking for getpwent()... yes

However, compilation fails because Android's headers looks like not expose declarations for getpwent() and setpwent():

  etc.c:294:5: error: call to undeclared function 'setpwent'
  etc.c:295:18: error: call to undeclared function 'getpwent'
  error: incompatible integer to pointer conversion

Same problem occurs with older versions of the gem, including 1.4.1 through 1.4.5.

The expected behavior

The extension should either (I think):

1. Compile successfully when these functions are available for the target android api; or
2. Correctly detect that they are unavailable and disable only the affected functionality.

Current detection appears to report getpwent() as available even though the generated extension cannot compile against the android headers.

Reproduction process

I try to install ruby using Android Termux

  gem install etc --no-document

Relevant output:

  checking for getpwent()... yes
  ...

  error: call to undeclared function 'setpwent'
  error: call to undeclared function 'getpwent'

The declarations in Termux's pwd.h are guarded by Android API availability macros, for example:

  struct passwd *getpwent(void) __INTRODUCED_IN(26);
  void setpwent(void) __INTRODUCED_IN(26);

The etc extension includes pwd.h when HAVE_GETPWENT is defined, but the declarations are not visible for the API configuration used while compiling Ruby.

This causes a mismatch between the feature detection performed by extconf.rb and the code generated by the extension.

Thanks