[Constriant solver] Don't adjust types in calls to @preconcurrency functions

When calling a `@preconcurrency` function, don't adjust the types of
parameters. Instead, we'll suppress or alter diagnostics later on to deal
with Sendable and global-actor mismatches.

Fixes the crash from rdar://95995193, but diagnostics need more work.

Author: DougGregor

lib/Sema/TypeCheckConcurrency.cpp

@@ -544,6 +544,10 @@ static bool isSendableClosure(
     if (forActorIsolation && explicitClosure->inheritsActorContext()) {
       return false;
     }
+
+    if (explicitClosure->isIsolatedByPreconcurrency() &&
+        !shouldDiagnoseExistingDataRaces(closure->getParent()))
+      return false;
   }
 
   if (auto type = closure->getType()) {
@@ -3981,12 +3985,19 @@ bool swift::contextRequiresStrictConcurrencyChecking(
 
   while (!dc->isModuleScopeContext()) {
     if (auto closure = dyn_cast<AbstractClosureExpr>(dc)) {
-      // A closure with an explicit global actor or nonindependent
+      // A closure with an explicit global actor, async, or Sendable
       // uses concurrency features.
       if (auto explicitClosure = dyn_cast<ClosureExpr>(closure)) {
         if (getExplicitGlobalActor(const_cast<ClosureExpr *>(explicitClosure)))
           return true;
 
+        // Don't take any more cues if this only got its type information by
+        // being provided to a `@preconcurrency` operation.
+        if (explicitClosure->isIsolatedByPreconcurrency()) {
+          dc = dc->getParent();
+          continue;
+        }
+
         if (auto type = getType(closure)) {
           if (auto fnType = type->getAs<AnyFunctionType>())
             if (fnType->isAsync() || fnType->isSendable())
@@ -4590,7 +4601,7 @@ static AnyFunctionType *applyUnsafeConcurrencyToFunctionType(
     if (addSendable || addMainActor) {
       newParamType = applyUnsafeConcurrencyToParameterType(
         param.getPlainType(), addSendable, addMainActor);
-    } else if (stripConcurrency) {
+    } else if (stripConcurrency && numApplies == 0) {
       newParamType = param.getPlainType()->stripConcurrency(
           /*recurse=*/false, /*dropGlobalActor=*/numApplies == 0);
     }

test/SILGen/preconcurrency.swift

@@ -14,8 +14,8 @@ func testModuleMethodWithSendable(any: Any) {
 
   // CHECK: function_ref @$s14preconcurrency1fyyypF : $@convention(thin) (@in_guaranteed Sendable) -> ()
   let _ = preconcurrency.f
-  // f(any)
-  // preconcurrency.f(any)
+  f(any)
+  preconcurrency.f(any)
 }
 
 // CHECK-LABEL: sil hidden [ossa] @$s14preconcurrency30testInstanceMethodWithSendable1c3anyyAA1CC_yptF : $@convention(thin) (@guaranteed C, @in_guaranteed Any) -> () {
@@ -25,5 +25,5 @@ func testInstanceMethodWithSendable(c: C, any: Any) {
   let _ = c.f
   let _ = C.f
   let _ = C.g
-//  c.f(any)
+  c.f(any)
 }