Sema: Refactor TypeChecker::typeCheckStmtConditionElement().

Use a switch statement to cover all the possible kinds of condition elements
and implement diagnostics in separate functions for each kind of condition
element.

NFC.

Author: tshortli

lib/Sema/TypeCheckStmt.cpp

@@ -784,46 +784,39 @@ ConcreteDeclRef TypeChecker::getReferencedDeclForHasSymbolCondition(Expr *E) {
   return ConcreteDeclRef();
 }
 
-bool TypeChecker::typeCheckStmtConditionElement(StmtConditionElement &elt,
-                                                bool &isFalsable,
-                                                DeclContext *dc) {
-  auto &Context = dc->getASTContext();
-
-  // Typecheck a #available or #unavailable condition.
-  if (elt.getKind() == StmtConditionElement::CK_Availability) {
-    isFalsable = true;
+static bool typeCheckHasSymbolStmtConditionElement(StmtConditionElement &elt,
+                                                   DeclContext *dc) {
+  auto Info = elt.getHasSymbolInfo();
+  auto E = Info->getSymbolExpr();
+  if (!E)
     return false;
-  }
 
-  // Typecheck a #_hasSymbol condition.
-  if (elt.getKind() == StmtConditionElement::CK_HasSymbol) {
-    isFalsable = true;
+  auto exprTy = TypeChecker::typeCheckExpression(E, dc);
+  Info->setSymbolExpr(E);
 
-    auto Info = elt.getHasSymbolInfo();
-    auto E = Info->getSymbolExpr();
-    if (!E)
-      return false;
-
-    auto exprTy = TypeChecker::typeCheckExpression(E, dc);
-    Info->setSymbolExpr(E);
+  if (!exprTy) {
+    Info->setInvalid();
+    return true;
+  }
 
-    if (!exprTy) {
-      Info->setInvalid();
-      return true;
-    }
+  Info->setReferencedDecl(
+      TypeChecker::getReferencedDeclForHasSymbolCondition(E));
+  return false;
+}
 
-    Info->setReferencedDecl(getReferencedDeclForHasSymbolCondition(E));
-    return false;
-  }
+static bool typeCheckBooleanStmtConditionElement(StmtConditionElement &elt,
+                                                 DeclContext *dc) {
+  Expr *E = elt.getBoolean();
+  assert(!E->getType() && "the bool condition is already type checked");
+  bool hadError = TypeChecker::typeCheckCondition(E, dc);
+  elt.setBoolean(E);
+  return hadError;
+}
 
-  if (auto E = elt.getBooleanOrNull()) {
-    assert(!E->getType() && "the bool condition is already type checked");
-    bool hadError = TypeChecker::typeCheckCondition(E, dc);
-    elt.setBoolean(E);
-    isFalsable = true;
-    return hadError;
-  }
-  assert(elt.getKind() != StmtConditionElement::CK_Boolean);
+static bool
+typeCheckPatternBindingStmtConditionElement(StmtConditionElement &elt,
+                                            bool &isFalsable, DeclContext *dc) {
+  auto &Context = dc->getASTContext();
 
   // This is cleanup goop run on the various paths where type checking of the
   // pattern binding fails.
@@ -871,6 +864,24 @@ bool TypeChecker::typeCheckStmtConditionElement(StmtConditionElement &elt,
   return hadError;
 }
 
+bool TypeChecker::typeCheckStmtConditionElement(StmtConditionElement &elt,
+                                                bool &isFalsable,
+                                                DeclContext *dc) {
+  switch (elt.getKind()) {
+  case StmtConditionElement::CK_Availability:
+    isFalsable = true;
+    return false;
+  case StmtConditionElement::CK_HasSymbol:
+    isFalsable = true;
+    return typeCheckHasSymbolStmtConditionElement(elt, dc);
+  case StmtConditionElement::CK_Boolean:
+    isFalsable = true;
+    return typeCheckBooleanStmtConditionElement(elt, dc);
+  case StmtConditionElement::CK_PatternBinding:
+    return typeCheckPatternBindingStmtConditionElement(elt, isFalsable, dc);
+  }
+}
+
 /// Type check the given 'if', 'while', or 'guard' statement condition.
 ///
 /// \param stmt The conditional statement to type-check, which will be modified