Get env stuff working on Windows

core/os/os2/env_windows.odin

@@ -1,50 +1,56 @@
 //+private
 package os2
 
+import "core:runtime"
 import "core:mem"
 import win32 "core:sys/windows"
 
-_lookup_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
+_get_env :: proc(key: string, allocator := context.allocator) -> (value: string, found: bool) {
 	if key == "" {
 		return
 	}
 	wkey := win32.utf8_to_wstring(key)
-	b := make([dynamic]u16, 100, context.temp_allocator)
-	for {
-		n := win32.GetEnvironmentVariableW(wkey, raw_data(b), u32(len(b)))
-		if n == 0 {
-			err := win32.GetLastError()
-			if err == win32.ERROR_ENVVAR_NOT_FOUND {
-				return "", false
-			}
-		}
 
-		if n <= u32(len(b)) {
-			value = win32.utf16_to_utf8(b[:n], allocator)
-			found = true
-			return
-		}
-
-		resize(&b, len(b)*2)
+	// https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-getenvironmentvariablew
+	buf_len := win32.GetEnvironmentVariableW(wkey, nil, 0)
+	if buf_len == 0 {
+		return
 	}
+	buf := make([dynamic]u16, buf_len, context.temp_allocator)
+	n := win32.GetEnvironmentVariableW(wkey, raw_data(buf), buf_len)
+	if n == 0 {
+		if win32.GetLastError() == win32.ERROR_ENVVAR_NOT_FOUND {
+			return "", false
+		}
+		value = ""
+		found = true
+		return
+	}
+
+	value = win32.utf16_to_utf8(buf[:n], allocator)
+	found = true
+	return
 }
 
 _set_env :: proc(key, value: string) -> bool {
 	k := win32.utf8_to_wstring(key)
 	v := win32.utf8_to_wstring(value)
 
+	// https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-setenvironmentvariablew
 	return bool(win32.SetEnvironmentVariableW(k, v))
 }
 
 _unset_env :: proc(key: string) -> bool {
 	k := win32.utf8_to_wstring(key)
+
+	// https://docs.microsoft.com/en-us/windows/win32/api/processenv/nf-processenv-setenvironmentvariablew
 	return bool(win32.SetEnvironmentVariableW(k, nil))
 }
 
 _clear_env :: proc() {
 	envs := environ(context.temp_allocator)
 	for env in envs {
-		for j in 1..<len(env) {
+		#no_bounds_check for j in 1..<len(env) {
 			if env[j] == '=' {
 				unset_env(env[0:j])
 				break
@@ -54,23 +60,33 @@ _clear_env :: proc() {
 }
 
 _environ :: proc(allocator := context.allocator) -> []string {
-	envs := win32.GetEnvironmentStringsW()
+	envs := ([^]u16)(win32.GetEnvironmentStringsW())
 	if envs == nil {
 		return nil
 	}
 	defer win32.FreeEnvironmentStringsW(envs)
 
-	r := make([dynamic]string, 0, 50, allocator)
-	for from, i, p := 0, 0, envs; true; i += 1 {
-		c := (^u16)(uintptr(p) + uintptr(i*2))^
-		if c == 0 {
-			if i <= from {
-				break
+	length := 0
+	n := 0
+	count_loop: for {
+		if envs[length] == 0 {
+			n += 1
+			if envs[length+1] == 0 {
+				break count_loop
 			}
-			w := mem.slice_ptr(mem.ptr_offset(p, from), i-from)
+		}
 
-			append(&r, win32.utf16_to_utf8(w, allocator))
-			from = i + 1
+		length += 1
+	}
+
+	r := make([dynamic]string, 0, n, allocator)
+	for offset, i := 0, 0; i < length && len(r) < n; i += 1 {
+		c := envs[i]
+		if c == 0 {
+			wstr := envs[offset:i]
+			append(&r, win32.utf16_to_utf8(wstr, allocator))
+			i += 1
+			offset = i
 		}
 	}