Introduce the Space Engine

Implement exhaustiveness checking in Sema with rich error messages.  The
algorithm used is a variant of the one described in Fengyun Liu's paper
"A Generic Algorithm for Checking Exhaustivity of Pattern Matching"
published in the EPFL conference, and Luc Maranget's seminal paper
"Warnings for Pattern Matching"

The Space Engine views pattern matching as a problem of projecting the
scrutinee of a pattern-match into a "Space", then iteratively
constructing a Space from the cases.  Taking the difference of this
master space and the covered spaces yields the "holes" left over or
reveals a completely covered space.

The algorithm also extends trivially to redundancy checks in patterns,
but that check is already implemented in SILGen and this algorithm does
not improve upon it.

Author: CodaFi

include/swift/AST/ASTPrinter.h

@@ -322,11 +322,6 @@ uint8_t getKeywordLen(tok keyword);
 /// Get <#code#>;
 StringRef getCodePlaceholder();
 
-/// Given an array of enum element decls, print them as case statements with
-/// placeholders as contents.
-void printEnumElementsAsCases(llvm::DenseSet<EnumElementDecl*> &UnhandledElements,
-                              llvm::raw_ostream &OS);
-
 } // namespace swift
 
 #endif // LLVM_SWIFT_AST_ASTPRINTER_H

include/swift/AST/DiagnosticsSema.def

@@ -2750,14 +2750,6 @@ ERROR(trailing_closure_requires_parens,none,
       "trailing closure requires parentheses for disambiguation in this"
       " context", ())
 
-ERROR(empty_switch_stmt,none,
-      "%select{'switch' statement body must have at least one 'case' or 'default' block; |}0"
-      "do you want to add "
-      "%select{missing cases?|a default case?}1",(bool, bool))
-ERROR(non_exhaustive_switch,none,
-      "%select{switch must be exhaustive, consider adding |do you want to add }0"
-      "%select{missing cases|a default clause}1"
-      "%select{|?}0", (bool, bool))
 //------------------------------------------------------------------------------
 // Type Check Patterns
 //------------------------------------------------------------------------------
@@ -3591,6 +3583,19 @@ WARNING(debug_long_closure_body, none,
         "closure took %0ms to type-check (limit: %1ms)",
         (unsigned, unsigned))
 
+//------------------------------------------------------------------------------
+// Pattern match diagnostics
+//------------------------------------------------------------------------------
+
+
+ERROR(empty_switch_stmt,none,
+      "'switch' statement body must have at least one 'case' or 'default' "
+      "block; do you want to add a default case?",())
+ERROR(non_exhaustive_switch,none,
+      "%select{switch must be exhaustive, consider adding |do you want to add }0"
+      "%select{missing cases|a default clause}1"
+      "%select{:|?}0 %2", (bool, bool, StringRef))
+
 #ifndef DIAG_NO_UNDEF
 # if defined(DIAG)
 #  undef DIAG

include/swift/AST/DiagnosticsSema.h

@@ -37,7 +37,6 @@ namespace swift {
     extern detail::DiagWithArguments<void Signature>::type ID;
 #include "DiagnosticsSema.def"
   }
-  void diagnoseMissingCases(ASTContext &Context, const SwitchStmt *SwitchS);
 }
 
 #endif

lib/AST/ASTPrinter.cpp

@@ -611,60 +611,6 @@ uint8_t swift::getKeywordLen(tok keyword) {
 
 StringRef swift::getCodePlaceholder() { return "<#code#>"; }
 
-void swift::
-printEnumElementsAsCases(llvm::DenseSet<EnumElementDecl*> &UnhandledElements,
-                         llvm::raw_ostream &OS) {
-  // Sort the missing elements to a vector because set does not guarantee orders.
-  SmallVector<EnumElementDecl*, 4> SortedElements;
-  SortedElements.insert(SortedElements.begin(), UnhandledElements.begin(),
-                        UnhandledElements.end());
-  std::sort(SortedElements.begin(),SortedElements.end(),
-            [](EnumElementDecl *LHS, EnumElementDecl *RHS) {
-              return LHS->getNameStr().compare(RHS->getNameStr()) < 0;
-            });
-
-  auto printPayloads = [](EnumElementDecl *EE, llvm::raw_ostream &OS) {
-    // If the enum element has no payloads, return.
-    auto TL = EE->getArgumentTypeLoc();
-    if (TL.isNull())
-      return;
-    TypeRepr* TR = EE->getArgumentTypeLoc().getTypeRepr();
-    if (auto *TTR = dyn_cast<TupleTypeRepr>(TR)) {
-      SmallVector<Identifier, 4> NameBuffer;
-      ArrayRef<Identifier> Names;
-      if (TTR->hasElementNames()) {
-        // Get the name from the tuple repr, if exist.
-        Names = TTR->getElementNames();
-      } else {
-        // Create same amount of empty names to the elements.
-        NameBuffer.resize(TTR->getNumElements());
-        Names = llvm::makeArrayRef(NameBuffer);
-      }
-      OS << "(";
-      // Print each element in the pattern match.
-      for (unsigned I = 0, N = Names.size(); I < N; I ++) {
-        auto Id = Names[I];
-        if (Id.empty())
-          OS << "_";
-        else
-          OS << tok::kw_let << " " << Id.str();
-        if (I + 1 != N) {
-          OS << ", ";
-        }
-      }
-      OS << ")";
-    }
-  };
-
-  // Print each enum element name.
-  std::for_each(SortedElements.begin(), SortedElements.end(),
-                [&](EnumElementDecl *EE) {
-                  OS << tok::kw_case << " ." << EE->getNameStr();
-                  printPayloads(EE, OS);
-                  OS <<": " << getCodePlaceholder() << "\n";
-                });
-}
-
 ASTPrinter &operator<<(ASTPrinter &printer, tok keyword) {
   SmallString<16> Buffer;
   llvm::raw_svector_ostream OS(Buffer);

lib/SILOptimizer/Mandatory/DataflowDiagnostics.cpp

@@ -83,12 +83,6 @@ static void diagnoseUnreachable(const SILInstruction *I,
       return;
     }
 
-    // A non-exhaustive switch would also produce an unreachable instruction.
-    if (L.isASTNode<SwitchStmt>()) {
-      diagnoseMissingCases(Context, L.getAsASTNode<SwitchStmt>());
-      return;
-    }
-
     if (auto *Guard = L.getAsASTNode<GuardStmt>()) {
       diagnose(Context, Guard->getBody()->getEndLoc(),
                diag::guard_body_must_not_fallthrough);