std/os: add the Setenv function

std/os/proc_unix.jule

@@ -12,4 +12,12 @@ use "std/sys"
 fn LookupEnv(key: str): (val: str, unset: bool) {
 	keyPtr := integ::StrToBytes(key)
 	ret unsafe { sys::Getenv(&keyPtr[0]) }
+}
+
+// Sets the value of the environment variable named by the key.
+// Reports whether it successful.
+fn Setenv(key: str, val: str): bool {
+	keyPtr := integ::StrToBytes(key)
+	valPtr := integ::StrToBytes(val)
+	ret unsafe { sys::Setenv(&keyPtr[0], &valPtr[0], 1) }
 }

std/os/proc_windows.jule

@@ -11,5 +11,23 @@ use "std/sys"
 // empty and the boolean will be true.
 fn LookupEnv(key: str): (val: str, unset: bool) {
 	keyPtr := integ::UTF16FromStr(key)
-	ret unsafe { sys::Getenv(&keyPtr[0]) }
+	mut n := u32(100)
+	for {
+		mut b := make([]u16, n)
+		n = unsafe { sys::GetEnvironmentVariable(&keyPtr[0], &b[0], u32(len(b))) }
+		if n == 0 && sys::GetLastError() == sys::ERROR_ENVVAR_NOT_FOUND {
+			ret "", false
+		}
+		if n <= u32(len(b)) {
+			ret integ::UTF16ToStr(b[:n]), true
+		}
+	}
+}
+
+// Sets the value of the environment variable named by the key.
+// Reports whether it successful.
+fn Setenv(key: str, val: str): bool {
+	keyPtr := integ::UTF16FromStr(key)
+	valPtr := integ::UTF16FromStr(val)
+	ret unsafe { sys::SetEnvironmentVariable(&keyPtr[0], &valPtr[0]) }
 }

std/sys/syscall_unix.jule

@@ -35,6 +35,7 @@ cpp unsafe fn mkdir(path: *integ::Char, mode: int): int
 cpp unsafe fn rmdir(path: *integ::Char): int
 cpp unsafe fn unlink(path: *integ::Char): int
 cpp unsafe fn getenv(key: *integ::Char): *integ::Char
+cpp unsafe fn setenv(key: *integ::Char, val: *integ::Char, overwrite: integ::Int): int
 
 // C's DIR.
 type Dir: cpp.DIR
@@ -109,4 +110,10 @@ unsafe fn Getenv(key: *byte): (val: str, unset: bool) {
 		val = integ::BytePtrToStr((*byte)(valPtr))
 	}
 	ret
+}
+
+// Wrapper for C's setenv function.
+// Reports whether it successful.
+unsafe fn Setenv(key: *byte, val: *byte, overwrite: integ::Int): bool {
+	ret cpp.setenv((*integ::Char)(key), (*integ::Char)(val), overwrite) == 0
 }

std/sys/syscall_windows.jule

@@ -30,7 +30,8 @@ cpp fn GetStdHandle(stdh: uintptr): *unsafe
 cpp unsafe fn CloseHandle(stdh: *unsafe): bool
 cpp unsafe fn _wstat(path: *integ::Wchar, mut handle: *cpp._stat): int
 cpp unsafe fn _wopen(path: *integ::Wchar, flag: int, mode: int): int
-cpp unsafe fn _wgetenv(key: *integ::Wchar): *integ::Wchar
+cpp unsafe fn GetEnvironmentVariableW(key: *integ::Wchar, mut out: *integ::Wchar, nSize: cpp.DWORD): cpp.DWORD
+cpp unsafe fn SetEnvironmentVariableW(key: *integ::Wchar, val: *integ::Wchar): bool
 cpp fn GetLastError(): u32
 cpp unsafe fn GetCurrentDirectoryW(bufflen: u32, buff: *integ::Wchar): u32
 cpp unsafe fn SetCurrentDirectoryW(path: *integ::Wchar): bool
@@ -157,14 +158,12 @@ fn FindClose(h: Handle): int {
 	ret unsafe { cpp.FindClose(cpp.HANDLE(h)) }
 }
 
-// Retrieves the value of the environment variable named by the key.
-// It returns the value, which will be empty if the variable is not present.
-unsafe fn Getenv(key: *u16): (val: str, unset: bool) {
-	valPtr := cpp._wgetenv((*integ::Wchar)(key))
-	if valPtr == nil {
-		unset = true
-	} else {
-		val = integ::U16PtrToStr((*u16)(valPtr))
-	}
-	ret
+// Windows's GetEnvironmentVariableW function.
+unsafe fn GetEnvironmentVariable(key: *u16, mut out: *u16, outLen: u32): u32 {
+	ret u32(cpp.GetEnvironmentVariableW((*integ::Wchar)(key), (*integ::Wchar)(out), cpp.DWORD(outLen)))
+}
+
+// Windows's SetEnvironmentVariableW function.
+unsafe fn SetEnvironmentVariable(key: *u16, val: *u16): bool {
+	ret cpp.SetEnvironmentVariableW((*integ::Wchar)(key), (*integ::Wchar)(val))
 }