Merge pull request #29879 from DougGregor/constraint-system-patterns

[Constraint system] Generate constraints from patterns

Author: DougGregor

lib/Sema/CSDiagnostics.cpp

@@ -2264,14 +2264,32 @@ bool ContextualFailure::diagnoseMissingFunctionCall() const {
     return false;
 
   auto *srcFT = getFromType()->getAs<FunctionType>();
-  if (!srcFT || !srcFT->getParams().empty())
+  if (!srcFT ||
+      !(srcFT->getParams().empty() ||
+        getLocator()->isLastElement<LocatorPathElt::PatternMatch>()))
     return false;
 
   auto toType = getToType();
   if (toType->is<AnyFunctionType>() ||
       !TypeChecker::isConvertibleTo(srcFT->getResult(), toType, getDC()))
     return false;
 
+  // Diagnose cases where the pattern tried to match associated values but
+  // the case we found had none.
+  if (auto match =
+          getLocator()->getLastElementAs<LocatorPathElt::PatternMatch>()) {
+    if (auto enumElementPattern =
+            dyn_cast<EnumElementPattern>(match->getPattern())) {
+      emitDiagnostic(enumElementPattern->getNameLoc(),
+                     diag::enum_element_pattern_assoc_values_mismatch,
+                     enumElementPattern->getName());
+      emitDiagnostic(enumElementPattern->getNameLoc(),
+                     diag::enum_element_pattern_assoc_values_remove)
+        .fixItRemove(enumElementPattern->getSubPattern()->getSourceRange());
+      return true;
+    }
+  }
+
   auto *anchor = getAnchor();
   emitDiagnostic(anchor->getLoc(), diag::missing_nullary_call,
                  srcFT->getResult())

lib/Sema/CSGen.cpp

@@ -2198,18 +2198,38 @@ namespace {
     ///
     /// \param pattern The pattern.
     Type getTypeForPattern(Pattern *pattern, ConstraintLocatorBuilder locator) {
+      // If there's no pattern, then we have an unknown subpattern. Create a
+      // type variable.
+      if (!pattern) {
+        return CS.createTypeVariable(CS.getConstraintLocator(locator),
+                                     TVO_CanBindToNoEscape);
+      }
+
+      // Local function that must be called for each "return" throughout this
+      // function, to set the type of the pattern.
+      auto setType = [&](Type type) {
+        CS.setType(pattern, type);
+        return type;
+      };
+
       switch (pattern->getKind()) {
       case PatternKind::Paren:
-        // Parentheses don't affect the type.
-        return getTypeForPattern(cast<ParenPattern>(pattern)->getSubPattern(),
-                                 locator);
+        // Parentheses don't affect the canonical type, but record them as
+        // type sugar.
+        return setType(
+            ParenType::get(
+              CS.getASTContext(),
+              getTypeForPattern(
+                cast<ParenPattern>(pattern)->getSubPattern(), locator)));
       case PatternKind::Var:
         // Var doesn't affect the type.
-        return getTypeForPattern(cast<VarPattern>(pattern)->getSubPattern(),
-                                 locator);
+        return setType(
+            getTypeForPattern(
+              cast<VarPattern>(pattern)->getSubPattern(), locator));
       case PatternKind::Any: {
-        return CS.createTypeVariable(CS.getConstraintLocator(locator),
-                                     TVO_CanBindToNoEscape);
+        return setType(
+            CS.createTypeVariable(CS.getConstraintLocator(locator),
+                                  TVO_CanBindToNoEscape));
       }
 
       case PatternKind::Named: {
@@ -2223,23 +2243,29 @@ namespace {
           ROK = OA->get();
         switch (optionalityOf(ROK)) {
         case ReferenceOwnershipOptionality::Required:
-          return TypeChecker::getOptionalType(var->getLoc(), varType);
+          return setType(TypeChecker::getOptionalType(var->getLoc(), varType));
         case ReferenceOwnershipOptionality::Allowed:
         case ReferenceOwnershipOptionality::Disallowed:
-          return varType;
+          return setType(varType);
         }
       }
 
       case PatternKind::Typed: {
         // FIXME: Need a better locator for a pattern as a base.
+        // Compute the type ascribed to the pattern.
         auto contextualPattern =
             ContextualPattern::forRawPattern(pattern, CurDC);
         Type type = TypeChecker::typeCheckPattern(contextualPattern);
         Type openedType = CS.openUnboundGenericType(type, locator);
 
-        // For a typed pattern, simply return the opened type of the pattern.
-        // FIXME: Error recovery if the type is an error type?
-        return openedType;
+        // Determine the subpattern type. It will be convertible to the
+        // ascribed type.
+        Type subPatternType =
+            getTypeForPattern(
+               cast<TypedPattern>(pattern)->getSubPattern(), locator);
+        CS.addConstraint(
+            ConstraintKind::Conversion, subPatternType, openedType, locator);
+        return setType(openedType);
       }
 
       case PatternKind::Tuple: {
@@ -2253,19 +2279,119 @@ namespace {
                                            LocatorPathElt::TupleElement(i)));
           tupleTypeElts.push_back(TupleTypeElt(eltTy, tupleElt.getLabel()));
         }
-        return TupleType::get(tupleTypeElts, CS.getASTContext());
+        return setType(TupleType::get(tupleTypeElts, CS.getASTContext()));
       }
-      
+
+      case PatternKind::OptionalSome: {
+        // The subpattern must have optional type.
+        Type subPatternType = getTypeForPattern(
+            cast<OptionalSomePattern>(pattern)->getSubPattern(), locator);
+
+        return setType(OptionalType::get(subPatternType));
+      }
+
+      case PatternKind::Is: {
+        auto isPattern = cast<IsPattern>(pattern);
+        Type subPatternType =
+            getTypeForPattern(isPattern->getSubPattern(), locator);
+
+        // Make sure we can cast from the subpattern type to the type we're
+        // checking; if it's impossible, fail.
+        if (Type castType =
+                resolveTypeReferenceInExpression(isPattern->getCastTypeLoc())) {
+          castType = CS.openUnboundGenericType(castType, locator);
+          CS.addConstraint(
+              ConstraintKind::CheckedCast, subPatternType, castType, locator);
+        }
+
+        return setType(subPatternType);
+      }
+
+      case PatternKind::Bool:
+        return setType(CS.getASTContext().getBoolDecl()->getDeclaredType());
+
+      case PatternKind::EnumElement: {
+        auto enumPattern = cast<EnumElementPattern>(pattern);
+
+        // Create a type variable to represent the pattern.
+        Type patternType =
+            CS.createTypeVariable(CS.getConstraintLocator(locator),
+                                  TVO_CanBindToNoEscape);
+
+        // Form the member constraint for a reference to a member of this
+        // type.
+        Type baseType;
+        Type memberType = CS.createTypeVariable(
+            CS.getConstraintLocator(locator),
+            TVO_CanBindToLValue | TVO_CanBindToNoEscape);
+        FunctionRefKind functionRefKind = FunctionRefKind::Compound;
+        if (!enumPattern->getParentType().isNull()) {
+          // Resolve the parent type.
+          Type parentType =
+            resolveTypeReferenceInExpression(enumPattern->getParentType());
+          parentType = CS.openUnboundGenericType(parentType, locator);
+
+          // Perform member lookup into the parent's metatype.
+          Type parentMetaType = MetatypeType::get(parentType);
+          CS.addValueMemberConstraint(
+              parentMetaType, enumPattern->getName(), memberType, CurDC,
+              functionRefKind, { },
+              locator.withPathElement(LocatorPathElt::PatternMatch(pattern)));
+
+          // Parent type needs to be convertible to the pattern type; this
+          // accounts for cases where the pattern type is existential.
+          CS.addConstraint(ConstraintKind::Conversion, parentType, patternType,
+                           locator);
+
+          baseType = parentType;
+        } else {
+          // Use the pattern type for member lookup.
+          CS.addUnresolvedValueMemberConstraint(
+              MetatypeType::get(patternType), enumPattern->getName(),
+              memberType, CurDC, functionRefKind,
+              locator.withPathElement(LocatorPathElt::PatternMatch(pattern)));
+
+          baseType = patternType;
+        }
+
+        if (auto subPattern = enumPattern->getSubPattern()) {
+          // When there is a subpattern, the member will have function type,
+          // and we're matching the type of that subpattern to the parameter
+          // types.
+          Type subPatternType = getTypeForPattern(subPattern, locator);
+          SmallVector<AnyFunctionType::Param, 8> params;
+          AnyFunctionType::decomposeInput(subPatternType, params);
+
+          // Remove parameter labels; they aren't used when matching cases,
+          // but outright conflicts will be checked during coercion.
+          for (auto &param : params) {
+            param = param.getWithoutLabel();
+          }
+
+          Type outputType = CS.createTypeVariable(
+              CS.getConstraintLocator(locator),
+              TVO_CanBindToNoEscape);
+          Type functionType = FunctionType::get(params, outputType);
+          CS.addConstraint(
+              ConstraintKind::Equal, functionType, memberType,
+              locator.withPathElement(LocatorPathElt::PatternMatch(pattern)));
+
+          CS.addConstraint(ConstraintKind::Conversion, outputType, baseType,
+                           locator);
+        }
+
+        return setType(patternType);
+      }
+
       // Refutable patterns occur when checking the PatternBindingDecls in an
       // if/let or while/let condition.  They always require an initial value,
       // so they always allow unspecified types.
-#define PATTERN(Id, Parent)
-#define REFUTABLE_PATTERN(Id, Parent) case PatternKind::Id:
-#include "swift/AST/PatternNodes.def"
+      case PatternKind::Expr:
         // TODO: we could try harder here, e.g. for enum elements to provide the
         // enum type.
-        return CS.createTypeVariable(CS.getConstraintLocator(locator),
-                                     TVO_CanBindToNoEscape);
+        return setType(
+            CS.createTypeVariable(
+              CS.getConstraintLocator(locator), TVO_CanBindToNoEscape));
       }
 
       llvm_unreachable("Unhandled pattern kind");
@@ -3845,11 +3971,7 @@ static bool generateInitPatternConstraints(
   auto locator =
       cs.getConstraintLocator(initializer, LocatorPathElt::ContextualType());
   Type patternType = cs.generateConstraints(pattern, locator);
-  if (!patternType)
-    return true;
-
-  // Record the type of this pattern.
-  cs.setType(pattern, patternType);
+  assert(patternType && "All patterns have a type");
 
   if (auto wrappedVar = target.getInitializationWrappedVar()) {
     // Add an equal constraint between the pattern type and the
@@ -4035,7 +4157,7 @@ void ConstraintSystem::bindVariablesInPattern(
   case PatternKind::Named: {
     auto var = cast<NamedPattern>(pattern)->getDecl();
 
-    /// Create a fresh type variable to describe the type of the
+    /// Create a fresh type variable to describe the type of the bound variable.
     Type varType = createTypeVariable(locator, TVO_CanBindToNoEscape);
 
     auto ROK = ReferenceOwnership::Strong;

lib/Sema/CSSimplify.cpp

@@ -1658,6 +1658,12 @@ ConstraintSystem::matchFunctionTypes(FunctionType *func1, FunctionType *func2,
             implodeParams(func2Params);
           }
         }
+      } else if (last->getKind() == ConstraintLocator::PatternMatch &&
+          isa<EnumElementPattern>(
+            last->castTo<LocatorPathElt::PatternMatch>().getPattern()) &&
+          isSingleTupleParam(ctx, func1Params) &&
+          canImplodeParams(func2Params)) {
+        implodeParams(func2Params);
       }
     }
 
@@ -3920,6 +3926,25 @@ bool ConstraintSystem::repairFailures(
     break;
   }
 
+  case ConstraintLocator::PatternMatch: {
+    // If either type is a hole, consider this fixed.
+    if (lhs->isHole() || rhs->isHole())
+      return true;
+
+    // If the left-hand side is a function type and the pattern is an enum
+    // element pattern, call it a contextual mismatch.
+    auto pattern = elt.castTo<LocatorPathElt::PatternMatch>().getPattern();
+    if (lhs->is<FunctionType>() && isa<EnumElementPattern>(pattern)) {
+      markAnyTypeVarsAsPotentialHoles(lhs);
+      markAnyTypeVarsAsPotentialHoles(rhs);
+
+      conversionsOrFixes.push_back(ContextualMismatch::create(
+          *this, lhs, rhs, getConstraintLocator(locator)));
+    }
+
+    break;
+  }
+
   default:
     break;
   }
@@ -5668,6 +5693,22 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
     }
   }
 
+  // If we are pattern-matching an enum element and we found any enum elements,
+  // ignore anything that isn't an enum element.
+  bool onlyAcceptEnumElements = false;
+  if (memberLocator &&
+      memberLocator->isLastElement<LocatorPathElt::PatternMatch>() &&
+      isa<EnumElementPattern>(
+          memberLocator->getLastElementAs<LocatorPathElt::PatternMatch>()
+            ->getPattern())) {
+    for (const auto &result: lookup) {
+      if (isa<EnumElementDecl>(result.getValueDecl())) {
+        onlyAcceptEnumElements = true;
+        break;
+      }
+    }
+  }
+
   // If the instance type is String bridged to NSString, compute
   // the type we'll look in for bridging.
   Type bridgedType;
@@ -5692,6 +5733,10 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
       return;
     }
 
+    // If we only accept enum elements but this isn't one, ignore it.
+    if (onlyAcceptEnumElements && !isa<EnumElementDecl>(decl))
+      return;
+
     // Dig out the instance type and figure out what members of the instance type
     // we are going to see.
     auto baseTy = candidate.getBaseType();
@@ -6039,6 +6084,25 @@ performMemberLookup(ConstraintKind constraintKind, DeclNameRef memberName,
     }
   }
 
+  // If we have candidates, and we're doing a member lookup for a pattern
+  // match, unwrap optionals and try again to allow implicit creation of
+  // optional "some" patterns (spelled "?").
+  if (result.ViableCandidates.empty() && result.UnviableCandidates.empty() &&
+      memberLocator &&
+      memberLocator->isLastElement<LocatorPathElt::PatternMatch>() &&
+      instanceTy->getOptionalObjectType() &&
+      baseObjTy->is<AnyMetatypeType>()) {
+    SmallVector<Type, 2> optionals;
+    Type instanceObjectTy = instanceTy->lookThroughAllOptionalTypes(optionals);
+    Type metaObjectType = MetatypeType::get(instanceObjectTy);
+    auto result = performMemberLookup(
+        constraintKind, memberName, metaObjectType,
+        functionRefKind, memberLocator, includeInaccessibleMembers);
+    result.numImplicitOptionalUnwraps = optionals.size();
+    result.actualBaseType = metaObjectType;
+    return result;
+  }
+
   // If we have no viable or unviable candidates, and we're generating,
   // diagnostics, rerun the query with inaccessible members included, so we can
   // include them in the unviable candidates list.
@@ -6369,8 +6433,13 @@ ConstraintSystem::SolutionKind ConstraintSystem::simplifyMemberConstraint(
   }
 
   SmallVector<Constraint *, 4> candidates;
+
   // If we found viable candidates, then we're done!
   if (!result.ViableCandidates.empty()) {
+    // If we had to look in a different type, use that.
+    if (result.actualBaseType)
+      baseTy = result.actualBaseType;
+
     // If only possible choice to refer to member is via keypath
     // dynamic member dispatch, let's delay solving this constraint
     // until constraint generation phase is complete, because