[Sema] Improve Optional-to-Any diagnostics for collections

When implicitly coercing a collection of optional elements to a collection of less-optional `Any` elements, e.g `[Any?]` to `[Any]`, emit a slightly better diagnostic:

Expression implicitly coerced from '[Any?]' to '[Any]'

and allow for silencing of the diagnostic with an explicit coercion, e.g `as [Any]`.

Author: hamishknight

lib/Sema/MiscDiagnostics.cpp

@@ -3493,6 +3493,18 @@ static void diagnoseUnintendedOptionalBehavior(TypeChecker &TC, const Expr *E,
       }
     }
 
+    /// Returns true iff the collection upcast coercion is an Optional-to-Any
+    /// coercion.
+    bool isOptionalToAnyCoercion(CollectionUpcastConversionExpr::ConversionPair
+                                   conversion) {
+      if (!conversion.OrigValue || !conversion.Conversion)
+        return false;
+
+      auto srcType = conversion.OrigValue->getType();
+      auto destType = conversion.Conversion->getType();
+      return isOptionalToAnyCoercion(srcType, destType);
+    }
+
     /// Looks through OptionalEvaluationExprs and InjectIntoOptionalExprs to
     /// find a child ErasureExpr, returning nullptr if no such child is found.
     /// Any intermediate OptionalEvaluationExprs will be marked as ignored.
@@ -3577,9 +3589,38 @@ static void diagnoseUnintendedOptionalBehavior(TypeChecker &TC, const Expr *E,
       emitSilenceOptionalAnyWarningWithCoercion(subExpr, destType);
     }
 
+    void visitCollectionUpcastExpr(CollectionUpcastConversionExpr *E,
+                                   OptionalToAnyCoercion coercion) {
+      // We only need to consider the valueConversion, as the Key type of a
+      // Dictionary cannot be implicitly coerced to Any.
+      auto valueConversion = E->getValueConversion();
+
+      // We're handling the coercion of the entire collection, so we don't need
+      // to re-visit a nested ErasureExpr for the value.
+      if (auto conversionExpr = valueConversion.Conversion)
+        if (auto *erasureExpr =
+              findErasureExprThroughOptionalInjections(conversionExpr))
+          IgnoredExprs.insert(erasureExpr);
+
+      if (coercion.shouldSuppressDiagnostic() ||
+          !isOptionalToAnyCoercion(valueConversion))
+        return;
+
+      auto subExpr = E->getSubExpr();
+
+      TC.diagnose(subExpr->getStartLoc(), diag::optional_to_any_coercion,
+                  /* from */ subExpr->getType(), /* to */ E->getType())
+        .highlight(subExpr->getSourceRange());
+
+      emitSilenceOptionalAnyWarningWithCoercion(subExpr, E->getType());
+    }
+
     void visitPossibleOptionalToAnyExpr(Expr *E,
                                         OptionalToAnyCoercion coercion) {
-      if (auto *erasureExpr = dyn_cast<ErasureExpr>(E)) {
+      if (auto *upcastExpr =
+          dyn_cast<CollectionUpcastConversionExpr>(E)) {
+        visitCollectionUpcastExpr(upcastExpr, coercion);
+      } else if (auto *erasureExpr = dyn_cast<ErasureExpr>(E)) {
         visitErasureExpr(erasureExpr, coercion);
       } else if (auto *optionalEvalExpr = dyn_cast<OptionalEvaluationExpr>(E)) {
         // The ErasureExpr could be nested within optional injections and

test/Sema/diag_unintended_optional_behavior.swift

@@ -132,27 +132,31 @@ func warnOptionalToIUOAny(_ a: Int?, _ b: Any??, _ c: Int???, _ d: Any????) {
 }
 
 func takesCollectionOfAny(_ a: [Any], _ d: [String : Any]) {}
+func takesCollectionOfOptionalAny(_ a: [Any?], _ d: [String : Any?]) {}
 
-func warnCollectionOfAny(_ a: [Int?], _ d: [String : Int?]) {
-  // https://bugs.swift.org/browse/SR-2928 - Collection casts from collections of optionals to collections of Any need custom handling
-  takesCollectionOfAny(a, d) // expected-warning {{expression implicitly coerced from 'Int?' to 'Any'}}
-  // expected-note@-1 {{provide a default value to avoid this warning}}{{25-25= ?? <#default value#>}}
-  // expected-note@-2 {{force-unwrap the value to avoid this warning}}{{25-25=!}}
-  // expected-note@-3 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{25-25= as Any}}
-  // expected-warning@-4 {{expression implicitly coerced from 'Int?' to 'Any'}}
-  // expected-note@-5 {{provide a default value to avoid this warning}}{{28-28= ?? <#default value#>}}
-  // expected-note@-6 {{force-unwrap the value to avoid this warning}}{{28-28=!}}
-  // expected-note@-7 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{28-28= as Any}}
-
-  // https://bugs.swift.org/browse/SR-2928 - Collection casts from collections of optionals to collections of Any need custom handling
-  takesCollectionOfAny(a as [Any], d as [String : Any]) // expected-warning {{expression implicitly coerced from 'Int?' to 'Any'}}
-  // expected-note@-1 {{provide a default value to avoid this warning}}{{25-25= ?? <#default value#>}}
-  // expected-note@-2 {{force-unwrap the value to avoid this warning}}{{25-25=!}}
-  // expected-note@-3 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{25-25= as Any}}
-  // expected-warning@-4 {{expression implicitly coerced from 'Int?' to 'Any'}}
-  // expected-note@-5 {{provide a default value to avoid this warning}}{{37-37= ?? <#default value#>}}
-  // expected-note@-6 {{force-unwrap the value to avoid this warning}}{{37-37=!}}
-  // expected-note@-7 {{explicitly cast to 'Any' with 'as Any' to silence this warning}}{{37-37= as Any}}
+func warnCollectionOfOptionalToAnyCoercion(_ a: [Int?], _ d: [String : Int?]) {
+  takesCollectionOfAny(a, d) // expected-warning {{expression implicitly coerced from '[Int?]' to '[Any]'}}
+  // expected-note@-1 {{explicitly cast to '[Any]' with 'as [Any]' to silence this warning}}{{25-25= as [Any]}}
+  // expected-warning@-2 {{expression implicitly coerced from '[String : Int?]' to '[String : Any]'}}
+  // expected-note@-3 {{explicitly cast to '[String : Any]' with 'as [String : Any]' to silence this warning}}{{28-28= as [String : Any]}}
+
+  takesCollectionOfAny(a as [Any], d as [String : Any])
+}
+
+func warnCollectionOfTripleOptionalToAnyCoercion(_ a: [Any???], _ d: [String: Any???]) {
+  takesCollectionOfAny(a, d) // expected-warning {{expression implicitly coerced from '[Any???]' to '[Any]'}}
+  // expected-note@-1 {{explicitly cast to '[Any]' with 'as [Any]' to silence this warning}}{{25-25= as [Any]}}
+  // expected-warning@-2 {{expression implicitly coerced from '[String : Any???]' to '[String : Any]'}}
+  // expected-note@-3 {{explicitly cast to '[String : Any]' with 'as [String : Any]' to silence this warning}}{{28-28= as [String : Any]}}
+
+  takesCollectionOfAny(a as [Any], d as [String : Any])
+
+  takesCollectionOfOptionalAny(a, d) // expected-warning {{expression implicitly coerced from '[Any???]' to '[Any?]'}}
+  // expected-note@-1 {{explicitly cast to '[Any?]' with 'as [Any?]' to silence this warning}}{{33-33= as [Any?]}}
+  // expected-warning@-2 {{expression implicitly coerced from '[String : Any???]' to '[String : Any?]'}}
+  // expected-note@-3 {{explicitly cast to '[String : Any?]' with 'as [String : Any?]' to silence this warning}}{{36-36= as [String : Any?]}}
+
+  takesCollectionOfOptionalAny(a as [Any?], d as [String : Any?])
 }
 
 func warnOptionalInStringInterpolationSegment(_ o : Int?) {