[Sema] Add Sema checks for detecting large integer literals that

overflow Builtin.Int2048 and add tests for checking the
correctness of the diagnostics.

lib/Sema/CSGen.cpp

@@ -1179,7 +1179,44 @@ namespace {
       auto protocol = CS.getTypeChecker().getLiteralProtocol(expr);
       if (!protocol)
         return nullptr;
-      
+
+      // Make sure that MaxIntegerType is defined if it would used later
+      // during constraint solving (CSApply).
+      if (isa<IntegerLiteralExpr>(expr) ||
+          (isa<MagicIdentifierLiteralExpr>(expr) &&
+           dyn_cast<MagicIdentifierLiteralExpr>(expr)->isColumn())) {
+
+        auto maxIntType = CS.TC.getMaxIntegerType(CS.DC);
+        if (maxIntType.isNull()) {
+          CS.TC.diagnose(expr->getLoc(), diag::no_MaxBuiltinIntegerType_found);
+          return nullptr;
+        }
+
+        // In the case of integer literal, make sure that the literal value
+        // will fit within the bit width of the maximum integer type.
+        if (IntegerLiteralExpr *intLit = dyn_cast<IntegerLiteralExpr>(expr)) {
+          unsigned maxWidth =
+              maxIntType->castTo<BuiltinIntegerType>()->getGreatestWidth();
+          APInt magnitude = intLit->getRawMagnitude();
+          unsigned magWidth = magnitude.getActiveBits();
+          bool isNegative = intLit->isNegative();
+
+          // Compute the literal bit width in the signed two's complement form.
+          // This is generally one more than the magnitude width, but is the
+          // same when the literal is of the form -2^i (for some Nat `i`).
+          unsigned signedLitWidth =
+              (isNegative && (magnitude.countTrailingZeros() == magWidth - 1))
+                  ? magWidth
+                  : (magWidth + 1);
+
+          if (signedLitWidth > maxWidth) { // overflow?
+            CS.TC.diagnose(expr->getLoc(),
+                           diag::integer_literal_overflows_maxwidth, maxWidth,
+                           signedLitWidth);
+            return nullptr;
+          }
+        }
+      }
 
       auto tv = CS.createTypeVariable(CS.getConstraintLocator(expr),
                                       TVO_PrefersSubtypeBinding);