Implementation for SE-0228: Fix ExpressibleByStringInterpolation

benchmark/single-source/StringInterpolation.swift

@@ -31,6 +31,14 @@ class RefTypePrintable : CustomStringConvertible {
   }
 }
 
+struct CustomString: ExpressibleByStringInterpolation {
+  var value: String
+
+  init(stringLiteral: String) {
+    self.value = stringLiteral
+  }
+}
+
 @inline(never)
 public func run_StringInterpolation(_ N: Int) {
   let reps = 100

docs/Literals.rst

@@ -136,8 +136,7 @@ to jump through.
 The default array literal type is always Array, and the default dictionary
 literal type is always Dictionary.
 
-String interpolations are a bit different: they try to individually convert
-each element of the interpolation to the type that adopts
-_ExpressibleByStringInterpolation, then calls the variadic
-``convertFromStringInterpolation`` to put them all together. The default type
+String interpolations are a bit different: they create an instance of 
+``T.StringInterpolation`` and append each segment to it, then initialize
+an instance of ``T`` with that instance. The default type
 for an interpolated literal without context is also ``StringLiteralType``.

include/swift/AST/Decl.h

@@ -3051,16 +3051,26 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   /// The table itself is lazily constructed and updated when
   /// lookupDirect() is called. The bit indicates whether the lookup
   /// table has already added members by walking the declarations in
-  /// scope.
+  /// scope; it should be manipulated through \c isLookupTablePopulated()
+  /// and \c setLookupTablePopulated().
   llvm::PointerIntPair<MemberLookupTable *, 1, bool> LookupTable;
 
   /// Prepare the lookup table to make it ready for lookups.
   void prepareLookupTable(bool ignoreNewExtensions);
 
+  /// True if the entries in \c LookupTable are complete--that is, if a
+  /// name is present, it contains all members with that name.
+  bool isLookupTablePopulated() const;
+  void setLookupTablePopulated(bool value);
+
   /// Note that we have added a member into the iterable declaration context,
   /// so that it can also be added to the lookup table (if needed).
   void addedMember(Decl *member);
 
+  /// Note that we have added an extension into the nominal type,
+  /// so that its members can eventually be added to the lookup table.
+  void addedExtension(ExtensionDecl *ext);
+
   /// \brief A lookup table used to find the protocol conformances of
   /// a given nominal type.
   mutable ConformanceLookupTable *ConformanceTable = nullptr;

include/swift/AST/DiagnosticsParse.def

@@ -1221,6 +1221,16 @@ ERROR(expected_type_after_as,none,
 ERROR(string_interpolation_extra,none,
       "extra tokens after interpolated string expression", ())
 
+// Interpolations with parameter labels or multiple values
+WARNING(string_interpolation_list_changing,none,
+      "interpolating multiple values will not form a tuple in Swift 5", ())
+NOTE(string_interpolation_list_insert_parens,none,
+      "insert parentheses to keep current behavior", ())
+WARNING(string_interpolation_label_changing,none,
+      "labeled interpolations will not be ignored in Swift 5", ())
+NOTE(string_interpolation_remove_label,none,
+      "remove %0 label to keep current behavior", (Identifier))
+
 // Keypath expressions.
 ERROR(expr_keypath_expected_lparen,PointsToFirstBadToken,
       "expected '(' following '#keyPath'", ())

include/swift/AST/DiagnosticsSema.def

@@ -1904,6 +1904,20 @@ NOTE(req_near_match_access,none,
      "make %0 %select{ERROR|private|private|non-public|non-public}1 to silence this "
      "warning", (DeclName, AccessLevel))
 
+// appendInterpolation methods
+ERROR(missing_append_interpolation,none,
+      "type conforming to 'StringInterpolationProtocol' does not implement "
+      "a valid 'appendInterpolation' method", ())
+WARNING(append_interpolation_static,none,
+      "'appendInterpolation' method will never be used because it is static", ())
+WARNING(append_interpolation_void_or_discardable,none,
+      "'appendInterpolation' method does not return 'Void' or have a "
+      "discardable result", ())
+WARNING(append_interpolation_access_control,none,
+      "'appendInterpolation' method is %select{private|fileprivate|internal|public|open}0, "
+      "but %1 is %select{private|fileprivate|internal|public|open}2",
+      (AccessLevel, DeclName, AccessLevel))
+
 // Protocols and existentials
 ERROR(assoc_type_outside_of_protocol,none,
       "associated type %0 can only be used with a concrete type or "
@@ -2749,10 +2763,10 @@ ERROR(optional_used_as_boolean,none,
      "test for '!= nil' instead", (Type))
 
 ERROR(interpolation_missing_proto,none,
-      "string interpolation requires the protocol '_ExpressibleByStringInterpolation' to be defined",
+      "string interpolation requires the protocol 'ExpressibleByStringInterpolation' to be defined",
       ())
 ERROR(interpolation_broken_proto,none,
-      "protocol '_ExpressibleByStringInterpolation' is broken",
+      "protocol 'ExpressibleByStringInterpolation' is broken",
       ())
 
 ERROR(object_literal_broken_proto,none,
@@ -3364,6 +3378,8 @@ ERROR(throw_in_illegal_context,none,
 
 ERROR(throwing_operator_without_try,none,
       "operator can throw but expression is not marked with 'try'", ())
+ERROR(throwing_interpolation_without_try,none,
+      "interpolation can throw but is not marked with 'try'", ())
 ERROR(throwing_call_without_try,none,
       "call can throw but is not marked with 'try'", ())
 NOTE(note_forgot_try,none,

include/swift/AST/Expr.h

@@ -57,6 +57,7 @@ namespace swift {
   class PatternBindingDecl;
   class ParameterList;
   class EnumElementDecl;
+  class CallExpr;
 
 enum class ExprKind : uint8_t {
 #define EXPR(Id, Parent) Id,
@@ -171,6 +172,12 @@ class alignas(8) Expr {
     IsSingleExtendedGraphemeCluster : 1
   );
 
+  SWIFT_INLINE_BITFIELD_FULL(InterpolatedStringLiteralExpr, LiteralExpr, 32+20,
+    : NumPadBits,
+    InterpolationCount : 20,
+    LiteralCapacity : 32
+  );
+
   SWIFT_INLINE_BITFIELD(DeclRefExpr, Expr, 2+2,
     Semantics : 2, // an AccessSemantics
     FunctionRefKind : 2
@@ -916,6 +923,41 @@ class StringLiteralExpr : public LiteralExpr {
   }
 };
 
+/// \brief Runs a series of statements which use or modify \c SubExpr 
+/// before it is given to the rest of the expression.
+/// 
+/// \c Body should begin with a \c VarDecl; this defines the variable 
+/// \c TapExpr will initialize at the beginning and read a result 
+/// from at the end. \c TapExpr creates a separate scope, then 
+/// assigns the result of \c SubExpr to the variable and runs \c Body 
+/// in it, returning the value of the variable after the \c Body runs.
+/// 
+/// Note: This is a minimal, preliminary design. Expect it to change.
+class TapExpr : public Expr {
+  Expr *SubExpr;
+  BraceStmt *Body;
+
+public:
+  TapExpr(Expr *SubExpr, BraceStmt *Body);
+
+  Expr * getSubExpr() const { return SubExpr; }
+  void setSubExpr(Expr * se) { SubExpr = se; }
+
+  /// \brief The variable which will be accessed and possibly modified by 
+  /// the \c Body. This is the first \c ASTNode in the \c Body.
+  VarDecl * getVar() const;
+
+  BraceStmt * getBody() const { return Body; }
+  void setBody(BraceStmt * b) { Body = b; }
+
+  SourceLoc getLoc() const { return SourceLoc(); }
+  SourceRange getSourceRange() const { return SourceRange(); }
+
+  static bool classof(const Expr *E) {
+    return E->getKind() == ExprKind::Tap;
+  }
+};
+
 /// InterpolatedStringLiteral - An interpolated string literal.
 ///
 /// An interpolated string literal mixes expressions (which are evaluated and
@@ -927,16 +969,37 @@ class StringLiteralExpr : public LiteralExpr {
 class InterpolatedStringLiteralExpr : public LiteralExpr {
   /// Points at the beginning quote.
   SourceLoc Loc;
-  MutableArrayRef<Expr *> Segments;
+  TapExpr *AppendingExpr;
   Expr *SemanticExpr;
 
 public:
-  InterpolatedStringLiteralExpr(SourceLoc Loc, MutableArrayRef<Expr *> Segments)
-    : LiteralExpr(ExprKind::InterpolatedStringLiteral, /*Implicit=*/false),
-      Loc(Loc), Segments(Segments), SemanticExpr() { }
-
-  MutableArrayRef<Expr *> getSegments() { return Segments; }
-  ArrayRef<Expr *> getSegments() const { return Segments; }
+  InterpolatedStringLiteralExpr(SourceLoc Loc, unsigned LiteralCapacity, 
+                                unsigned InterpolationCount,
+                                TapExpr *AppendingExpr)
+      : LiteralExpr(ExprKind::InterpolatedStringLiteral, /*Implicit=*/false),
+        Loc(Loc), AppendingExpr(AppendingExpr), SemanticExpr() {
+    Bits.InterpolatedStringLiteralExpr.InterpolationCount = InterpolationCount;
+    Bits.InterpolatedStringLiteralExpr.LiteralCapacity = LiteralCapacity;
+  }
+
+  /// \brief Retrieve the value of the literalCapacity parameter to the
+  /// initializer.
+  unsigned getLiteralCapacity() const {
+    return Bits.InterpolatedStringLiteralExpr.LiteralCapacity;
+  }
+
+  /// \brief Retrieve the value of the interpolationCount parameter to the
+  /// initializer.
+  unsigned getInterpolationCount() const {
+    return Bits.InterpolatedStringLiteralExpr.InterpolationCount;
+  }
+
+  /// \brief A block containing expressions which call
+  /// \c StringInterpolationProtocol methods to append segments to the
+  /// string interpolation. The first node in \c Body should be an uninitialized
+  /// \c VarDecl; the other statements should append to it.
+  TapExpr * getAppendingExpr() const { return AppendingExpr; }
+  void setAppendingExpr(TapExpr * AE) { AppendingExpr = AE; }
 
   /// \brief Retrieve the expression that actually evaluates the resulting
   /// string, typically with a series of '+' operations.
@@ -951,6 +1014,9 @@ class InterpolatedStringLiteralExpr : public LiteralExpr {
     // token, so the range should be (Start == End).
     return Loc;
   }
+
+  /// \brief Call the \c callback with information about each segment in turn.
+  void forEachSegment(ASTContext &Ctx, llvm::function_ref<void(bool, CallExpr *)> callback);
 
   static bool classof(const Expr *E) {
     return E->getKind() == ExprKind::InterpolatedStringLiteral;

include/swift/AST/ExprNodes.def

@@ -188,7 +188,8 @@ EXPR(EditorPlaceholder, Expr)
 EXPR(ObjCSelector, Expr)
 EXPR(KeyPath, Expr)
 UNCHECKED_EXPR(KeyPathDot, Expr)
-LAST_EXPR(KeyPathDot)
+EXPR(Tap, Expr)
+LAST_EXPR(Tap)
 
 #undef EXPR_RANGE
 #undef LITERAL_EXPR

include/swift/AST/KnownIdentifiers.def

@@ -165,7 +165,12 @@ IDENTIFIER_(builtinUTF16StringLiteral)
 IDENTIFIER_(builtinStringLiteral)
 IDENTIFIER(StringLiteralType)
 IDENTIFIER(stringInterpolation)
-IDENTIFIER(stringInterpolationSegment)
+IDENTIFIER(StringInterpolation)
+IDENTIFIER(literalCapacity)
+IDENTIFIER(interpolationCount)
+IDENTIFIER(appendLiteral)
+IDENTIFIER(appendInterpolation)
+IDENTIFIER_WITH_NAME(dollarInterpolation, "$interpolation")
 IDENTIFIER(arrayLiteral)
 IDENTIFIER(dictionaryLiteral)
 IDENTIFIER_(getBuiltinLogicValue)

include/swift/AST/KnownProtocols.def

@@ -70,13 +70,15 @@ PROTOCOL(Decodable)
 PROTOCOL_(ObjectiveCBridgeable)
 PROTOCOL_(DestructorSafeContainer)
 
+PROTOCOL(StringInterpolationProtocol)
+
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByArrayLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByBooleanLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByDictionaryLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByExtendedGraphemeClusterLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByFloatLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByIntegerLiteral)
-EXPRESSIBLE_BY_LITERAL_PROTOCOL_(ExpressibleByStringInterpolation)
+EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByStringInterpolation)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByStringLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByNilLiteral)
 EXPRESSIBLE_BY_LITERAL_PROTOCOL(ExpressibleByUnicodeScalarLiteral)

include/swift/Parse/Parser.h

@@ -1219,8 +1219,11 @@ class Parser {
   StringRef copyAndStripUnderscores(StringRef text);
 
   ParserStatus parseStringSegments(SmallVectorImpl<Lexer::StringSegment> &Segments,
-                                   SmallVectorImpl<Expr*> &Exprs,
-                                   Token EntireTok);
+                                   Token EntireTok,
+                                   VarDecl *InterpolationVar,
+                                   SmallVectorImpl<ASTNode> &Stmts,
+                                   unsigned &LiteralCapacity,
+                                   unsigned &InterpolationCount);
 
   /// Parse an argument label `identifier ':'`, if it exists.
   ///

lib/AST/ASTDumper.cpp

@@ -1839,10 +1839,10 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
   }
   void visitInterpolatedStringLiteralExpr(InterpolatedStringLiteralExpr *E) {
     printCommon(E, "interpolated_string_literal_expr");
-    for (auto Segment : E->getSegments()) {
-      OS << '\n';
-      printRec(Segment);
-    }
+    PrintWithColorRAII(OS, LiteralValueColor) << " literal_capacity=" 
+      << E->getLiteralCapacity() << " interpolation_count="
+      << E->getInterpolationCount() << '\n';
+    printRec(E->getAppendingExpr());
     printSemanticExpr(E->getSemanticExpr());
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
@@ -2644,6 +2644,19 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
     printCommon(E, "key_path_dot_expr");
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
+
+  void visitTapExpr(TapExpr *E) {
+    printCommon(E, "tap_expr");
+    PrintWithColorRAII(OS, DeclColor) << " var=";
+    printDeclRef(E->getVar());
+    OS << '\n';
+
+    printRec(E->getSubExpr());
+    OS << '\n';
+
+    printRec(E->getBody(), E->getVar()->getDeclContext()->getASTContext());
+    PrintWithColorRAII(OS, ParenthesisColor) << ')';
+  }
 };
 
 } // end anonymous namespace

lib/AST/ASTWalker.cpp

@@ -446,9 +446,9 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
   Expr *visitInterpolatedStringLiteralExpr(InterpolatedStringLiteralExpr *E) {
     HANDLE_SEMANTIC_EXPR(E);
 
-    for (auto &Segment : E->getSegments()) {
-      if (Expr *Seg = doIt(Segment))
-        Segment = Seg;
+    if (auto oldAppendingExpr = E->getAppendingExpr()) {
+      if (auto appendingExpr = doIt(oldAppendingExpr))
+        E->setAppendingExpr(dyn_cast<TapExpr>(appendingExpr));
       else
         return nullptr;
     }
@@ -1050,6 +1050,28 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
 
   Expr *visitKeyPathDotExpr(KeyPathDotExpr *E) { return E; }
 
+  Expr *visitTapExpr(TapExpr *E) {
+    if (auto oldSubExpr = E->getSubExpr()) {
+      if (auto subExpr = doIt(oldSubExpr)) {
+        E->setSubExpr(subExpr);
+      }
+      else {
+        return nullptr;
+      }
+    }
+
+    if (auto oldBody = E->getBody()) {
+      if (auto body = doIt(oldBody)) {
+        E->setBody(dyn_cast<BraceStmt>(body));
+      }
+      else {
+        return nullptr;
+      }
+    }
+
+    return E;
+  }
+
   //===--------------------------------------------------------------------===//
   //                           Everything Else
   //===--------------------------------------------------------------------===//

lib/AST/Decl.cpp

@@ -3000,6 +3000,8 @@ void NominalTypeDecl::addExtension(ExtensionDecl *extension) {
   // Add to the end of the list.
   LastExtension->NextExtension.setPointer(extension);
   LastExtension = extension;
+
+  addedExtension(extension);
 }
 
 auto NominalTypeDecl::getStoredProperties(bool skipInaccessible) const