improve os.getenvs

[waruqi]

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---

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[gemini-code-assist]

Summary of Changes

Hello @waruqi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the os.getenvs functionality by moving the core logic for environment variable parsing and processing from Lua to C. This change aims to boost performance and enhance the reliability of environment variable handling, ensuring proper trimming and consistent capitalization, especially for Windows 'PATH' variables. As a result, the Lua-side code is streamlined, directly receiving a structured table of environment variables from the C implementation.

Highlights

• Performance Improvement: The parsing and processing of environment variables have been migrated from Lua to C, which is expected to result in faster execution and improved efficiency.
• Enhanced Robustness: Centralized logic for trimming whitespace from environment variable keys and values, along with consistent handling of Windows 'PATH' capitalization, is now managed at the C level, leading to more reliable behavior.
• Simplified Lua API: The Lua-side os.getenvs function has been removed, as its functionality is now directly handled by the C implementation, which populates a Lua table with parsed key-value pairs, simplifying the Lua codebase.

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[gemini-code-assist]

Code Review

This pull request refactors os.getenvs by moving the environment variable parsing logic from Lua to C, which should provide a nice performance boost. The C implementation is well-structured. My review includes a couple of suggestions to improve it further: one for const-correctness to enhance type safety and remove unsafe casts, and another to simplify pushing values to the Lua stack. The corresponding changes in the Lua code to remove the old implementation are correct.

[gemini-code-assist]

The xm_os_getenvs_trim function should be const-correct since it does not modify the content of the string, only the pointers to its start and end. Changing the signature to accept tb_char_t const** improves type safety and allows removing the unsafe casts in xm_os_getenvs_process_line at lines 99 and 103.

Suggested change

	static tb_void_t xm_os_getenvs_trim(tb_char_t** sstr, tb_char_t** estr)
	{
	// check
	tb_assert(sstr && estr && *sstr && *estr);
	tb_char_t* p = *sstr;
	tb_char_t* e = *estr;
	// trim left
	while (p < e && tb_isspace(*p))
	p++;
	// trim right
	while (e > p && tb_isspace(*(e - 1)))
	e--;
	// save trimmed string
	*sstr = p;
	*estr = e;
	}
	static tb_void_t xm_os_getenvs_trim(tb_char_t const** sstr, tb_char_t const** estr)
	{
	// check
	tb_assert(sstr && estr && *sstr && *estr);
	tb_char_t const* p = *sstr;
	tb_char_t const* e = *estr;
	// trim left
	while (p < e && tb_isspace(*p))
	p++;
	// trim right
	while (e > p && tb_isspace(*(e - 1)))
	e--;
	// save trimmed string
	*sstr = p;
	*estr = e;
	}

[gemini-code-assist]

This if/else block can be simplified. lua_pushlstring with a length of 0 correctly pushes an empty string, which is equivalent to lua_pushliteral(lua, ""). You can replace these four lines with a single call.

    lua_pushlstring(lua, value_start, value_len);