[stdlib] Add CT @in Macro/Builtin (#2662)

* [stdlib] Add CT `@in` Macro/Builtin

lib/std/core/builtin.c3

@@ -93,6 +93,21 @@ macro usz bitsizeof($Type) @builtin @const => $Type.sizeof * 8u;
 
 macro usz @bitsizeof(#expr) @builtin @const => $sizeof(#expr) * 8u;
 
+<*
+ Compile-time check for whether a set of constants contains a certain expression.
+
+ @param #needle : "The expression whose value should be located."
+*>
+macro bool @in(#needle, ...) @builtin @const
+{
+    $for var $x = 0; $x < $vacount; $x++:
+        $assert $defined(#needle == $vaconst[$x])
+            : "Index %s: types '%s' (needle) and '%s' are not equatable", $x, $typeof(#needle), $typeof($vaconst[$x]);
+        $if #needle == $vaconst[$x]: return true; $endif
+    $endfor
+    return false;
+}
+
 <*
  Convert an `any` type to a type, returning an failure if there is a type mismatch.
 

releasenotes.md

@@ -27,6 +27,7 @@
 
 ### Stdlib changes
 - Add `ThreadPool` join function to wait for all threads to finish in the pool without destroying the threads.
+- Add `@in` compile-time macro to check for a value in a variable list of constants. #2662
 - Return of Thread/Mutex/CondVar `destroy()` is now "@maydiscard" and should be ignored. It will return void in 0.8.0.
 - Return of Mutex `unlock()` and `lock()` is now "@maydiscard" and should be ignored. They will return void in 0.8.0.
 - Return of ConditionVariable `signal()` `broadcast()` and `wait()` are now "@maydiscard". They will return void in 0.8.0.

test/unit/stdlib/core/builtintests.c3

@@ -224,3 +224,13 @@ fn void test_ct_min_max()
 	assert(@max(0, 0, 1.234, 1.2345, 0.2) == 1.2345);
 	assert(@max(127.9999999, 45 + 46, bitsizeof(uint128)) == 128);
 }
+
+const usz[] MY_OK_VALUES = { 128, 256, 384, 512 };
+fn void test_in()
+{
+    $assert @in(384, ...MY_OK_VALUES);
+    $assert !@in(123, ...MY_OK_VALUES);
+    $assert @in(384, 128, 256, 384, 512);
+    $assert @in("love", "joy", "cheer", "love", "friend");
+    $assert !@in("hate", "joy", "cheer", "love", "friend");
+}