[CSSimplify] Detect and diagnose passing a tuple to pack expansion that expects individual arguments

Author: xedin

lib/Sema/CSFix.cpp

@@ -2745,7 +2745,9 @@ AllowGlobalActorMismatch::create(ConstraintSystem &cs, Type fromType,
 
 bool DestructureTupleToMatchPackExpansionParameter::diagnose(
     const Solution &solution, bool asNote) const {
-  return false;
+  DestructureTupleToUseWithPackExpansionParameter failure(solution, ParamShape,
+                                                          getLocator());
+  return failure.diagnose(asNote);
 }
 
 DestructureTupleToMatchPackExpansionParameter *

lib/Sema/CSSimplify.cpp

@@ -5684,6 +5684,12 @@ bool ConstraintSystem::repairFailures(
     if (rhs->is<PackType>()) {
       ArrayRef tmpPath(path);
 
+      // Ignore argument/parameter type conversion mismatch if we already
+      // detected a tuple splat issue.
+      if (hasFixFor(loc,
+                    FixKind::DestructureTupleToMatchPackExpansionParameter))
+        return true;
+
       // Path would end with `ApplyArgument`.
       auto *argsLoc = getConstraintLocator(anchor, tmpPath.drop_back());
       if (hasFixFor(argsLoc, FixKind::RemoveExtraneousArguments) ||
@@ -13339,6 +13345,21 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifySameShapeConstraint(
         auto argLoc =
             loc->castLastElementTo<LocatorPathElt::ApplyArgToParam>();
 
+        auto argPack = type1->castTo<PackType>();
+        auto paramPack = type2->castTo<PackType>();
+
+        // Tailed diagnostic to explode tuples.
+        if (argPack->getNumElements() == 1) {
+          if (auto *tuple = argPack->getElementType(0)->getAs<TupleType>()) {
+            if (tuple->getNumElements() == paramPack->getNumElements()) {
+              return recordShapeFix(
+                  DestructureTupleToMatchPackExpansionParameter::create(
+                      *this, paramPack, loc),
+                  /*impact=*/2 * paramPack->getNumElements());
+            }
+          }
+        }
+
         auto numArgs = shape1->castTo<PackType>()->getNumElements();
         auto numParams = shape2->castTo<PackType>()->getNumElements();
 

test/Constraints/pack-expansion-expressions.swift

@@ -330,22 +330,40 @@ func test_pack_expansions_with_closures() {
 }
 
 // rdar://107151854 - crash on invalid due to specialized pack expansion
-func test_pack_expansion_specialization() {
+func test_pack_expansion_specialization(tuple: (Int, String, Float)) {
   struct Data<each T> {
-    init(_: repeat each T) {} // expected-note 3 {{'init(_:)' declared here}}
+    init(_: repeat each T) {} // expected-note 4 {{'init(_:)' declared here}}
     init(vals: repeat each T) {} // expected-note {{'init(vals:)' declared here}}
+    init<each U>(x: Int, _: repeat each T, y: repeat each U) {} // expected-note 3 {{'init(x:_:y:)' declared here}}
   }
 
   _ = Data<Int>() // expected-error {{missing argument for parameter #1 in call}}
   _ = Data<Int>(0) // Ok
   _ = Data<Int, String>(42, "") // Ok
   _ = Data<Int>(42, "") // expected-error {{extra argument in call}}
   _ = Data<Int, String>((42, ""))
-  // expected-error@-1 {{initializer expects 2 separate arguments; remove extra parentheses to change tuple into separate arguments}}
+  // expected-error@-1 {{value pack expansion at parameter #0 expects 2 separate arguments; remove extra parentheses to change tuple into separate arguments}} {{25-26=}} {{32-33=}}
   _ = Data<Int, String, Float>(vals: (42, "", 0))
-  // expected-error@-1 {{initializer expects 3 separate arguments; remove extra parentheses to change tuple into separate arguments}}
+  // expected-error@-1 {{value pack expansion at parameter #0 expects 3 separate arguments; remove extra parentheses to change tuple into separate arguments}} {{38-39=}} {{48-49=}}
   _ = Data<Int, String, Float>((vals: 42, "", 0))
-  // expected-error@-1 {{initializer expects 3 separate arguments; remove extra parentheses to change tuple into separate arguments}}
+  // expected-error@-1 {{value pack expansion at parameter #0 expects 3 separate arguments; remove extra parentheses to change tuple into separate arguments}} {{32-33=}} {{48-49=}}
+  _ = Data<Int, String, Float>(tuple)
+  // expected-error@-1 {{value pack expansion at parameter #0 expects 3 separate arguments}}
+  _ = Data<Int, String, Float>(x: 42, tuple)
+  // expected-error@-1 {{value pack expansion at parameter #1 expects 3 separate arguments}}
+  _ = Data<Int, String, Float>(x: 42, tuple, y: 1, 2, 3)
+  // expected-error@-1 {{value pack expansion at parameter #1 expects 3 separate arguments}}
+  _ = Data<Int, String, Float>(x: 42, (42, "", 0), y: 1, 2, 3)
+  // expected-error@-1 {{value pack expansion at parameter #1 expects 3 separate arguments}} {{39-40=}} {{49-50=}}
+
+  struct Ambiguity<each T> {
+    func test(_: repeat each T) -> Int { 42 }
+    // expected-note@-1 {{value pack expansion at parameter #0 expects 3 separate arguments}}
+    func test(_: repeat each T) -> String { "" }
+    // expected-note@-1 {{value pack expansion at parameter #0 expects 3 separate arguments}}
+  }
+
+  _ = Ambiguity<Int, String, Float>().test(tuple) // expected-error {{no exact matches in call to instance method 'test'}}
 }
 
 // rdar://107280056 - "Ambiguous without more context" with opaque return type + variadics