Linux: util: Free BSTR after conversion to String

The same call to SysFreeString happens in the Windows counterpart.

Solves the following leaks found by valgrind:

    ==213075== 40 bytes in 1 blocks are definitely lost in loss record 4 of 13
    ==213075==    at 0x483A77F: malloc (vg_replace_malloc.c:307)
    ==213075==    by 0x5B03395: ???
    ==213075==    by 0x5AFC77E: ???
    ==213075==    by 0x12C766: hassle_rs::intellisense::ffi::IDxcCursor::get_display_name (macros.rs:108)
    ==213075==    by 0x116373: hassle_rs::intellisense::wrapper::DxcCursor::get_display_name (wrapper.rs:236)
    ==213075==    by 0x11286D: intellisense_tu::main (intellisense-tu.rs:33)
    ==213075==    by 0x11371A: core::ops::function::FnOnce::call_once (function.rs:227)
    ==213075==    by 0x11348D: std::sys_common::backtrace::__rust_begin_short_backtrace (backtrace.rs:137)
    ==213075==    by 0x111E10: std::rt::lang_start::{{closure}} (rt.rs:66)
    ==213075==    by 0x150A20: call_once<(),Fn<()>> (function.rs:259)
    ==213075==    by 0x150A20: do_call<&Fn<()>,i32> (panicking.rs:373)
    ==213075==    by 0x150A20: try<i32,&Fn<()>> (panicking.rs:337)
    ==213075==    by 0x150A20: catch_unwind<&Fn<()>,i32> (panic.rs:379)
    ==213075==    by 0x150A20: std::rt::lang_start_internal (rt.rs:51)
    ==213075==    by 0x111DE6: std::rt::lang_start (rt.rs:65)
    ==213075==
    ==213075== 56 (16 direct, 40 indirect) bytes in 1 blocks are definitely lost in loss record 5 of 13
    ==213075==    at 0x483ADEF: operator new(unsigned long) (vg_replace_malloc.c:342)
    ==213075==    by 0x4FD058D: ???
    ==213075==    by 0x4FC04D9: ???
    ==213075==    by 0x40112DD: call_init.part.0 (in /usr/lib/ld-2.32.so)
    ==213075==    by 0x40113C7: _dl_init (in /usr/lib/ld-2.32.so)
    ==213075==    by 0x4A100E4: _dl_catch_exception (in /usr/lib/libc-2.32.so)
    ==213075==    by 0x4015704: dl_open_worker (in /usr/lib/ld-2.32.so)
    ==213075==    by 0x4A10087: _dl_catch_exception (in /usr/lib/libc-2.32.so)
    ==213075==    by 0x4014F3D: _dl_open (in /usr/lib/ld-2.32.so)
    ==213075==    by 0x489434B: ??? (in /usr/lib/libdl-2.32.so)
    ==213075==    by 0x4A10087: _dl_catch_exception (in /usr/lib/libc-2.32.so)
    ==213075==    by 0x4A10152: _dl_catch_error (in /usr/lib/libc-2.32.so)
    ==213075==
    ==213075== 124 bytes in 3 blocks are definitely lost in loss record 9 of 13
    ==213075==    at 0x483A77F: malloc (vg_replace_malloc.c:307)
    ==213075==    by 0x5B03395: ???
    ==213075==    by 0x5AFC77E: ???
    ==213075==    by 0x12C766: hassle_rs::intellisense::ffi::IDxcCursor::get_display_name (macros.rs:108)
    ==213075==    by 0x116373: hassle_rs::intellisense::wrapper::DxcCursor::get_display_name (wrapper.rs:236)
    ==213075==    by 0x112F63: intellisense_tu::main (intellisense-tu.rs:52)
    ==213075==    by 0x11371A: core::ops::function::FnOnce::call_once (function.rs:227)
    ==213075==    by 0x11348D: std::sys_common::backtrace::__rust_begin_short_backtrace (backtrace.rs:137)
    ==213075==    by 0x111E10: std::rt::lang_start::{{closure}} (rt.rs:66)
    ==213075==    by 0x150A20: call_once<(),Fn<()>> (function.rs:259)
    ==213075==    by 0x150A20: do_call<&Fn<()>,i32> (panicking.rs:373)
    ==213075==    by 0x150A20: try<i32,&Fn<()>> (panicking.rs:337)
    ==213075==    by 0x150A20: catch_unwind<&Fn<()>,i32> (panic.rs:379)
    ==213075==    by 0x150A20: std::rt::lang_start_internal (rt.rs:51)
    ==213075==    by 0x111DE6: std::rt::lang_start (rt.rs:65)

Fixes: 94fbad7 ("Support libdxcompiler.so on Linux (#5)")

src/os.rs

@@ -6,6 +6,7 @@ mod os_defs {
     };
 
     pub use winapi::um::combaseapi::CoTaskMemFree;
+    pub use winapi::um::oleauto::SysFreeString;
 }
 
 #[cfg(not(windows))]
@@ -26,6 +27,12 @@ mod os_defs {
         // https://github.com/microsoft/DirectXShaderCompiler/blob/a8d9780046cb64a1cea842fa6fc28a250e3e2c09/include/dxc/Support/WinAdapter.h#L46
         libc::free(p)
     }
+
+    #[allow(non_snake_case)]
+    pub unsafe fn SysFreeString(p: BSTR) {
+        // https://github.com/microsoft/DirectXShaderCompiler/blob/a8d9780046cb64a1cea842fa6fc28a250e3e2c09/include/dxc/Support/WinAdapter.h#L48-L50
+        libc::free(p as _)
+    }
 }
 
 pub use os_defs::*;

src/utils.rs

@@ -1,9 +1,9 @@
-use crate::os::{BSTR, HRESULT, LPSTR, LPWSTR, WCHAR};
+use crate::os::{SysFreeString, BSTR, HRESULT, LPSTR, LPWSTR, WCHAR};
 use crate::wrapper::*;
 use thiserror::Error;
 
 #[cfg(windows)]
-use winapi::um::oleauto::{SysFreeString, SysStringLen};
+use winapi::um::oleauto::SysStringLen;
 
 pub(crate) fn to_wide(msg: &str) -> Vec<WCHAR> {
     widestring::WideCString::from_str(msg).unwrap().into_vec()
@@ -33,7 +33,9 @@ pub(crate) fn from_bstr(string: BSTR) -> String {
     // TODO (Marijn): This does NOT cover embedded NULLs:
     // https://docs.microsoft.com/en-us/windows/win32/api/oleauto/nf-oleauto-sysstringlen#remarks
     // Fortunately BSTRs are only used in names currently, which _likely_ don't include NULL characters (like binary data)
-    from_lpstr(string as LPSTR)
+    let result = from_lpstr(string as LPSTR);
+    unsafe { SysFreeString(string) };
+    result
 }
 
 pub(crate) fn from_lpstr(string: LPSTR) -> String {