Sema: Emit diagnostics when walking into collection literals with defaulted types

Resolves #60011

Tests: add verification for emitted fixit, a flag for no availability checking; add expected warnings

Gardening: clean up diagnoseTypeDefaultedCollectionExpr function

Author: simanerush

lib/Sema/MiscDiagnostics.cpp

@@ -105,13 +105,18 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
     SmallPtrSet<DeclRefExpr*, 4> AlreadyDiagnosedBitCasts;
 
     bool IsExprStmt;
+    // A flag to avoid rediagnosing the literal during the walk.
+    bool ShouldDiagnoseTypeDefaultedCollections;
 
   public:
     ASTContext &Ctx;
     const DeclContext *DC;
 
-    DiagnoseWalker(const DeclContext *DC, bool isExprStmt)
-      : IsExprStmt(isExprStmt), Ctx(DC->getASTContext()), DC(DC) {}
+    DiagnoseWalker(const DeclContext *DC, bool isExprStmt,
+                   bool shouldDiagnoseTypeDefaultedCollections)
+        : IsExprStmt(isExprStmt), ShouldDiagnoseTypeDefaultedCollections(
+                                      shouldDiagnoseTypeDefaultedCollections),
+          Ctx(DC->getASTContext()), DC(DC) {}
 
     std::pair<bool, Pattern*> walkToPatternPre(Pattern *P) override {
       return { false, P };
@@ -124,6 +129,19 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
     bool shouldWalkIntoTapExpression() override { return false; }
 
     std::pair<bool, Expr *> walkToExprPre(Expr *E) override {
+
+      // When walked into a type defaulted collection expression, check if it
+      // should be diagnosed.
+      if (auto collection = dyn_cast<CollectionExpr>(E)) {
+        if (collection->isTypeDefaulted() &&
+            ShouldDiagnoseTypeDefaultedCollections) {
+          // Only diagnose type defaulted collection if was not diagnosed
+          // before.
+          diagnoseTypeDefaultedCollectionExpr(
+              const_cast<CollectionExpr *>(collection), Ctx, true);
+        }
+      }
+
       // See through implicit conversions of the expression.  We want to be able
       // to associate the parent of this expression with the ultimate callee.
       auto Base = E;
@@ -420,23 +438,34 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
       return false;
     }
 
-    /// We have a collection literal with a defaulted type, e.g. of [Any].  Emit
-    /// an error if it was inferred to this type in an invalid context, which is
-    /// one in which the parent expression is not itself a collection literal.
-    void checkTypeDefaultedCollectionExpr(CollectionExpr *c) {
-      // If the parent is a non-expression, or is not itself a literal, then
-      // produce an error with a fixit to add the type as an explicit
-      // annotation.
-      if (c->getNumElements() == 0)
-        Ctx.Diags.diagnose(c->getLoc(), diag::collection_literal_empty)
-          .highlight(c->getSourceRange());
-      else {
+    /// Diagnose a collection literal with a defaulted type such as \c [Any].
+    static void diagnoseTypeDefaultedCollectionExpr(CollectionExpr *c,
+                                                    ASTContext &ctx,
+                                                    bool diagnoseAsWarning) {
+      // Produce a diagnostic with a fixit to add the defaulted type as an
+      // explicit annotation.
+      auto &diags = ctx.Diags;
+
+      if (c->getNumElements() == 0) {
+        InFlightDiagnostic inFlight =
+            diags.diagnose(c->getLoc(), diag::collection_literal_empty);
+        inFlight.highlight(c->getSourceRange());
+
+        if (diagnoseAsWarning) {
+          inFlight.limitBehavior(DiagnosticBehavior::Warning);
+        }
+      } else {
         assert(c->getType()->hasTypeRepr() &&
                "a defaulted type should always be printable");
-        Ctx.Diags.diagnose(c->getLoc(), diag::collection_literal_heterogeneous,
-                           c->getType())
-          .highlight(c->getSourceRange())
-          .fixItInsertAfter(c->getEndLoc(), " as " + c->getType()->getString());
+        InFlightDiagnostic inFlight = diags.diagnose(
+            c->getLoc(), diag::collection_literal_heterogeneous, c->getType());
+        inFlight.highlight(c->getSourceRange());
+        inFlight.fixItInsertAfter(c->getEndLoc(),
+                                  " as " + c->getType()->getString());
+
+        if (diagnoseAsWarning) {
+          inFlight.limitBehavior(DiagnosticBehavior::Warning);
+        }
       }
     }
 
@@ -1308,18 +1337,21 @@ static void diagSyntacticUseRestrictions(const Expr *E, const DeclContext *DC,
     }
   };
 
-  DiagnoseWalker Walker(DC, isExprStmt);
-  const_cast<Expr *>(E)->walk(Walker);
+  bool shouldDiagnoseTypeDefaultedCollections = true;
 
-  // Diagnose uses of collection literals with defaulted types at the top
-  // level.
-  if (auto collection
-        = dyn_cast<CollectionExpr>(E->getSemanticsProvidingExpr())) {
+  if (auto collection =
+          dyn_cast<CollectionExpr>(E->getSemanticsProvidingExpr())) {
     if (collection->isTypeDefaulted()) {
-      Walker.checkTypeDefaultedCollectionExpr(
-        const_cast<CollectionExpr *>(collection));
+      DiagnoseWalker::diagnoseTypeDefaultedCollectionExpr(
+          const_cast<CollectionExpr *>(collection), DC->getASTContext(), false);
+      // The expression was diagnosed, thus there is no need to diagnose it
+      // again.
+      shouldDiagnoseTypeDefaultedCollections = false;
     }
   }
+
+  DiagnoseWalker Walker(DC, isExprStmt, shouldDiagnoseTypeDefaultedCollections);
+  const_cast<Expr *>(E)->walk(Walker);
 }
 
 

test/Constraints/array_literal.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift
+// RUN: %target-typecheck-verify-swift -disable-availability-checking
 
 struct IntList : ExpressibleByArrayLiteral {
   typealias Element = Int
@@ -145,16 +145,49 @@ func defaultToAny(i: Int, s: String) {
   let _: [Any] = [1, "a", 3.5]
   let _: [Any] = [1, "a", [3.5, 3.7, 3.9]]
   let _: [Any] = [1, "a", [3.5, "b", 3]]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
   let _: [Any] = [1, [2, [3]]]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
 
   let _: [Any?] = [1, "a", nil, 3.5]
   let _: [Any?] = [1, "a", nil, [3.5, 3.7, 3.9]]
   let _: [Any?] = [1, "a", nil, [3.5, "b", nil]]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
   let _: [Any?] = [1, [2, [3]]]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
   let _: [Any?] = [1, nil, [2, nil, [3]]]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
 
   let a6 = [B(), C()]
   let _: Int = a6 // expected-error{{value of type '[A]'}}
+  
+  let a7: some Collection = [1, "Swift"]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}} {{41-41= as [Any]}}
+  let a8: (any Sequence)? = [1, "Swift"]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
+  let a9: any Sequence = [1, nil, "Swift"]
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
+  func test<T>(_: [T]) {}
+
+  test([])
+  // expected-warning@-1{{empty collection literal requires an explicit type}}
+  test([1, nil, ""])
+  // expected-warning@-1{{heterogeneous collection literal could only be inferred to '[Any?]'; add explicit type annotation if this is intentional}}
+
+  func test<T>() -> [T]? {
+    []
+  }
+
+  _ = test() ?? []
+  // expected-warning@-1{{empty collection literal requires an explicit type}}
+  _ = ["Swift", 1, test([])]
+  // expected-warning@-1 {{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
+  // expected-warning@-2{{empty collection literal requires an explicit type}}
+
+  func f(_ b: Bool) {
+    let _ = b ? [] : []
+    // expected-warning@-1{{empty collection literal requires an explicit type}}
+  }
 }
 
 func noInferAny(iob: inout B, ioc: inout C) {

test/Constraints/casts.swift

@@ -337,6 +337,7 @@ func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [Strin
 
   // The array can also be inferred to be [Any].
   _ = ([] ?? []) as Array // expected-warning {{left side of nil coalescing operator '??' has non-optional type '[Any]', so the right side is never used}}
+  // expected-warning@-1{{empty collection literal requires an explicit type}}
 
   // rdar://88334481 – Don't apply the compatibility logic for collection literals.
   typealias Magic<T> = T

test/Constraints/casts_swift6.swift

@@ -57,6 +57,7 @@ func test_compatibility_coercions(_ arr: [Int], _ optArr: [Int]?, _ dict: [Strin
 
   // The array can also be inferred to be [Any].
   _ = ([] ?? []) as Array // expected-warning {{left side of nil coalescing operator '??' has non-optional type '[Any]', so the right side is never used}}
+  // expected-warning@-1 {{empty collection literal requires an explicit type}}
 
   // Cases from rdar://88334481
   typealias Magic<T> = T

test/Constraints/construction.swift

@@ -172,6 +172,7 @@ SR_5245(s: SR_5245.S(f: [.e1, .e2]))
 
 // rdar://problem/34670592 - Compiler crash on heterogeneous collection literal
 _ = Array([1, "hello"]) // Ok
+// expected-warning@-1 {{heterogeneous collection literal could only be inferred to '[Any]'; add explicit type annotation if this is intentional}}
 
 func init_via_non_const_metatype(_ s1: S1.Type) {
   _ = s1(i: 42) // expected-error {{initializing from a metatype value must reference 'init' explicitly}} {{9-9=.init}}

test/Constraints/subscript.swift

@@ -104,6 +104,7 @@ extension Int {
 let _ = 1["1"]  // expected-error {{ambiguous use of 'subscript(_:)'}}
 
 let squares = [ 1, 2, 3 ].reduce([:]) { (dict, n) in
+  // expected-warning@-1 {{empty collection literal requires an explicit type}}
   var dict = dict
   dict[n] = n * n
   return dict

test/IDE/print_usrs_opaque_types.swift

@@ -9,29 +9,34 @@
 func testUnifyingGenericParams<T, U>(x: T) -> some Collection where T == U {
   // expected-warning@-1 {{same-type requirement makes generic parameters 'U' and 'T' equivalent}}
   return []
+  // expected-warning@-1 {{empty collection literal requires an explicit type}}
 }
 
 // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test0C22UnifyingGenericParams21xQrx_tSlRz7ElementQzRs_r0_lF
 func testUnifyingGenericParams2<T, U>(x: T) -> some Collection where T: Collection, U == T.Element {
   return []
+  // expected-warning@-1 {{empty collection literal requires an explicit type}}
 }
 
 // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test0C24ConcretizingGenericParam1xQrSi_tSiRszlF
 func testConcretizingGenericParam<T>(x: T) -> some Collection where T == Int {
   // expected-warning@-1 {{same-type requirement makes generic parameter 'T' non-generic}}
   return []
+  // expected-warning@-1 {{empty collection literal requires an explicit type}}
 }
 
 struct GenericContext<T> {
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test14GenericContextV0c8UnifyingD6Params1xQrx_tqd__RszlF
   func testUnifyingGenericParams<U>(x: T) -> some Collection where T == U {
     // expected-warning@-1 {{same-type requirement makes generic parameters 'U' and 'T' equivalent}}
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test14GenericContextV0c8UnifyingD7Params21xQrx_tSlRz7ElementQzRsd__lF
   func testUnifyingGenericParams2<U>(x: T) -> some Collection where T: Collection, U == T.Element {
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test14GenericContextVyQrxcqd__Rszluip
@@ -40,6 +45,7 @@ struct GenericContext<T> {
     // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test14GenericContextVyQrxcqd__Rszluig
     get {
       return []
+      // expected-warning@-1 {{empty collection literal requires an explicit type}}
     }
   }
 }
@@ -48,6 +54,7 @@ extension GenericContext where T == Int {
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test14GenericContextVAASiRszlE0c12ConcretizingD5Param1xQrSi_tF
   func testConcretizingGenericParam(x: T) -> some Collection {
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 }
 
@@ -58,19 +65,22 @@ extension TooGenericTooContext where T == U {
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test010TooGenericD7ContextVAAq_RszrlE0c8UnifyingE6Params1xQrx_tF
   func testUnifyingGenericParams(x: T) -> some Collection {
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 }
 
 extension TooGenericTooContext where T: Collection, U == T.Element {
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test010TooGenericD7ContextVAASlRz7ElementQzRs_rlE0c8UnifyingE7Params21xQrx_tF
   func testUnifyingGenericParams2(x: T) -> some Collection {
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 }
 extension TooGenericTooContext where T == Int {
   // CHECK: [[@LINE+1]]:{{[0-9]+}} s:14swift_ide_test010TooGenericD7ContextVAASiRszrlE0c12ConcretizingE5Param1xQrSi_tF
   func testConcretizingGenericParam(x: T) -> some Collection {
     return []
+    // expected-warning@-1 {{empty collection literal requires an explicit type}}
   }
 }