std::dynamic_lib: Fix Windows error handling

This is a [breaking-change] since `std::dynamic_lib::dl` is now
private.

When `LoadLibraryW()` fails, original code called `errno()` to get error
code.  However, there was local allocation of `Vec` before
`LoadLibraryW()`, and it drops before `errno()`, and the drop
(deallocation) changed `errno`! Therefore `dynamic_lib::open()` thought
it always succeeded.
This commit fixes the issue.

This commit also sets Windows error mode during `LoadLibrary()` to
prevent "dll load failed" dialog.

src/libstd/dynamic_lib.rs

@@ -52,13 +52,7 @@ impl DynamicLibrary {
     /// Lazily open a dynamic library. When passed None it gives a
     /// handle to the calling process
     pub fn open(filename: Option<&Path>) -> Result<DynamicLibrary, String> {
-        unsafe {
+        let maybe_library = dl::open(filename.map(|path| path.as_vec()));
-            let maybe_library = dl::check_for_errors_in(|| {
-                match filename {
-                    Some(name) => dl::open_external(name.as_vec()),
-                    None => dl::open_internal()
-                }
-            });
 
         // The dynamic library must not be constructed if there is
         // an error opening the library so the destructor does not
@@ -68,7 +62,6 @@ impl DynamicLibrary {
             Ok(handle) => Ok(DynamicLibrary { handle: handle })
         }
     }
-    }
 
     /// Prepends a path to this process's search path for dynamic libraries
     pub fn prepend_search_path(path: &Path) {
@@ -198,8 +191,7 @@ mod test {
           target_os = "ios",
           target_os = "freebsd",
           target_os = "dragonfly"))]
-pub mod dl {
+mod dl {
-    pub use self::Rtld::*;
     use prelude::v1::*;
 
     use ffi::{self, CString};
@@ -207,13 +199,26 @@ pub mod dl {
     use libc;
     use ptr;
 
-    pub unsafe fn open_external(filename: &[u8]) -> *mut u8 {
+    pub fn open(filename: Option<&[u8]>) -> Result<*mut u8, String> {
-        let s = CString::from_slice(filename);
+        check_for_errors_in(|| {
-        dlopen(s.as_ptr(), Lazy as libc::c_int) as *mut u8
+            unsafe {
+                match filename {
+                    Some(filename) => open_external(filename),
+                    None => open_internal(),
+                }
+            }
+        })
     }
 
-    pub unsafe fn open_internal() -> *mut u8 {
+    const LAZY: libc::c_int = 1;
-        dlopen(ptr::null(), Lazy as libc::c_int) as *mut u8
+
+    unsafe fn open_external(filename: &[u8]) -> *mut u8 {
+        let s = CString::from_slice(filename);
+        dlopen(s.as_ptr(), LAZY) as *mut u8
+    }
+
+    unsafe fn open_internal() -> *mut u8 {
+        dlopen(ptr::null(), LAZY) as *mut u8
     }
 
     pub fn check_for_errors_in<T, F>(f: F) -> Result<T, String> where
@@ -249,14 +254,6 @@ pub mod dl {
         dlclose(handle as *mut libc::c_void); ()
     }
 
-    #[derive(Copy)]
-    pub enum Rtld {
-        Lazy = 1,
-        Now = 2,
-        Global = 256,
-        Local = 0,
-    }
-
     #[link_name = "dl"]
     extern {
         fn dlopen(filename: *const libc::c_char,
@@ -269,11 +266,13 @@ pub mod dl {
 }
 
 #[cfg(target_os = "windows")]
-pub mod dl {
+mod dl {
     use iter::IteratorExt;
     use libc;
+    use libc::consts::os::extra::ERROR_CALL_NOT_IMPLEMENTED;
     use ops::FnOnce;
     use os;
+    use option::Option::{self, Some, None};
     use ptr;
     use result::Result;
     use result::Result::{Ok, Err};
@@ -282,19 +281,75 @@ pub mod dl {
     use str;
     use string::String;
     use vec::Vec;
+    use sys::c::compat::kernel32::SetThreadErrorMode;
 
-    pub unsafe fn open_external(filename: &[u8]) -> *mut u8 {
+    pub fn open(filename: Option<&[u8]>) -> Result<*mut u8, String> {
-        // Windows expects Unicode data
+        // disable "dll load failed" error dialog.
+        let mut use_thread_mode = true;
+        let prev_error_mode = unsafe {
+            // SEM_FAILCRITICALERRORS 0x01
+            let new_error_mode = 1;
+            let mut prev_error_mode = 0;
+            // Windows >= 7 supports thread error mode.
+            let result = SetThreadErrorMode(new_error_mode, &mut prev_error_mode);
+            if result == 0 {
+                let err = os::errno();
+                if err as libc::c_int == ERROR_CALL_NOT_IMPLEMENTED {
+                    use_thread_mode = false;
+                    // SetThreadErrorMode not found. use fallback solution: SetErrorMode()
+                    // Note that SetErrorMode is process-wide so this can cause race condition!
+                    // However, since even Windows APIs do not care of such problem (#20650),
+                    // we just assume SetErrorMode race is not a great deal.
+                    prev_error_mode = SetErrorMode(new_error_mode);
+                }
+            }
+            prev_error_mode
+        };
+
+        unsafe {
+            SetLastError(0);
+        }
+
+        let result = match filename {
+            Some(filename) => {
                 let filename_str = str::from_utf8(filename).unwrap();
                 let mut filename_str: Vec<u16> = filename_str.utf16_units().collect();
                 filename_str.push(0);
-        LoadLibraryW(filename_str.as_ptr() as *const libc::c_void) as *mut u8
+                let result = unsafe {
+                    LoadLibraryW(filename_str.as_ptr() as *const libc::c_void)
+                };
+                // beware: Vec/String may change errno during drop!
+                // so we get error here.
+                if result == ptr::null_mut() {
+                    let errno = os::errno();
+                    Err(os::error_string(errno))
+                } else {
+                    Ok(result as *mut u8)
+                }
+            }
+            None => {
+                let mut handle = ptr::null_mut();
+                let succeeded = unsafe {
+                    GetModuleHandleExW(0 as libc::DWORD, ptr::null(), &mut handle)
+                };
+                if succeeded == libc::FALSE {
+                    let errno = os::errno();
+                    Err(os::error_string(errno))
+                } else {
+                    Ok(handle as *mut u8)
+                }
+            }
+        };
+
+        unsafe {
+            if use_thread_mode {
+                SetThreadErrorMode(prev_error_mode, ptr::null_mut());
+            } else {
+                SetErrorMode(prev_error_mode);
+            }
         }
 
-    pub unsafe fn open_internal() -> *mut u8 {
+        result
-        let mut handle = ptr::null_mut();
-        GetModuleHandleExW(0 as libc::DWORD, ptr::null(), &mut handle);
-        handle as *mut u8
     }
 
     pub fn check_for_errors_in<T, F>(f: F) -> Result<T, String> where
@@ -326,10 +381,10 @@ pub mod dl {
         fn SetLastError(error: libc::size_t);
         fn LoadLibraryW(name: *const libc::c_void) -> *mut libc::c_void;
         fn GetModuleHandleExW(dwFlags: libc::DWORD, name: *const u16,
-                              handle: *mut *mut libc::c_void)
+                              handle: *mut *mut libc::c_void) -> libc::BOOL;
-                              -> *mut libc::c_void;
         fn GetProcAddress(handle: *mut libc::c_void,
                           name: *const libc::c_char) -> *mut libc::c_void;
         fn FreeLibrary(handle: *mut libc::c_void);
+        fn SetErrorMode(uMode: libc::c_uint) -> libc::c_uint;
     }
 }

src/libstd/sys/windows/c.rs

@@ -226,6 +226,7 @@ pub mod compat {
     /// * `CreateSymbolicLinkW`: Windows XP, Windows Server 2003
     /// * `GetFinalPathNameByHandleW`: Windows XP, Windows Server 2003
     pub mod kernel32 {
+        use libc::c_uint;
         use libc::types::os::arch::extra::{DWORD, LPCWSTR, BOOLEAN, HANDLE};
         use libc::consts::os::extra::ERROR_CALL_NOT_IMPLEMENTED;
 
@@ -249,6 +250,12 @@ pub mod compat {
                 unsafe { SetLastError(ERROR_CALL_NOT_IMPLEMENTED as DWORD); 0 }
             }
         }
+
+        compat_fn! {
+            kernel32::SetThreadErrorMode(_dwNewMode: DWORD, _lpOldMode: *mut DWORD) -> c_uint {
+                unsafe { SetLastError(ERROR_CALL_NOT_IMPLEMENTED as DWORD); 0 }
+            }
+        }
     }
 }