Adds a warning when assigning a value in a conditional

DMCompiler/Compiler/DM/DMParser.cs

@@ -1065,7 +1065,12 @@ private DMASTProcStatementSet[] ProcSetEnd(bool allowMultiple) {
                 Consume(TokenType.DM_LeftParenthesis, "Expected '('");
                 BracketWhitespace();
                 DMASTExpression? condition = Expression();
-                if (condition == null) Error("Expected a condition");
+                if (condition == null) {
+                    Error("Expected a condition");
+                }
+                if (condition is DMASTAssign) {
+                    DMCompiler.Emit(WarningCode.AssignmentInConditional, condition.Location, "Assignment in conditional");
+                }
                 BracketWhitespace();
                 ConsumeRightParenthesis();
                 Whitespace();

DMCompiler/DMStandard/DefaultPragmaConfig.dm

@@ -33,4 +33,4 @@
 #pragma EmptyBlock notice
 #pragma EmptyProc disabled // NOTE: If you enable this in OD's default pragma config file, it will emit for OD's DMStandard. Put it in your codebase's pragma config file.
 #pragma UnsafeClientAccess disabled // NOTE: Only checks for unsafe accesses like "client.foobar" and doesn't consider if the client was already null-checked earlier in the proc
-
+#pragma AssignmentInConditional warning 

OpenDreamShared/Compiler/CompilerError.cs

@@ -59,6 +59,7 @@ public enum WarningCode {
         EmptyProc = 3101,
         UnsafeClientAccess = 3200,
         SuspiciousSwitchCase = 3201, // "else if" cases are actually valid DM, they just spontaneously end the switch context and begin an if-else ladder within the else case of the switch
+        AssignmentInConditional = 3202,
 
         // 4000 - 4999 are reserved for runtime configuration. (TODO: Runtime doesn't know about configs yet!)
     }