[Refactoring] Extract CollapseNestedIfStmt to its own file

lib/Refactoring/Refactoring.cpp

@@ -1846,74 +1846,6 @@ bool RefactoringActionReplaceBodiesWithFatalError::performChange() {
   return false;
 }
 
-static std::pair<IfStmt *, IfStmt *>
-findCollapseNestedIfTarget(ResolvedCursorInfoPtr CursorInfo) {
-  auto StmtStartInfo = dyn_cast<ResolvedStmtStartCursorInfo>(CursorInfo);
-  if (!StmtStartInfo)
-    return {};
-
-  // Ensure the statement is 'if' statement. It must not have 'else' clause.
-  IfStmt *OuterIf = dyn_cast<IfStmt>(StmtStartInfo->getTrailingStmt());
-  if (!OuterIf)
-    return {};
-  if (OuterIf->getElseStmt())
-    return {};
-
-  // The body must contain a sole inner 'if' statement.
-  auto Body = dyn_cast_or_null<BraceStmt>(OuterIf->getThenStmt());
-  if (!Body || Body->getNumElements() != 1)
-    return {};
-
-  IfStmt *InnerIf =
-      dyn_cast_or_null<IfStmt>(Body->getFirstElement().dyn_cast<Stmt *>());
-  if (!InnerIf)
-    return {};
-
-  // Inner 'if' statement also cannot have 'else' clause.
-  if (InnerIf->getElseStmt())
-    return {};
-
-  return {OuterIf, InnerIf};
-}
-
-bool RefactoringActionCollapseNestedIfStmt::isApplicable(
-    ResolvedCursorInfoPtr CursorInfo, DiagnosticEngine &Diag) {
-  return findCollapseNestedIfTarget(CursorInfo).first;
-}
-
-bool RefactoringActionCollapseNestedIfStmt::performChange() {
-  auto Target = findCollapseNestedIfTarget(CursorInfo);
-  if (!Target.first)
-    return true;
-  auto OuterIf = Target.first;
-  auto InnerIf = Target.second;
-
-  EditorConsumerInsertStream OS(
-      EditConsumer, SM,
-      Lexer::getCharSourceRangeFromSourceRange(SM, OuterIf->getSourceRange()));
-
-  OS << tok::kw_if << " ";
-
-  // Emit conditions.
-  bool first = true;
-  for (auto &C : llvm::concat<StmtConditionElement>(OuterIf->getCond(),
-                                                    InnerIf->getCond())) {
-    if (first)
-      first = false;
-    else
-      OS << ", ";
-    OS << Lexer::getCharSourceRangeFromSourceRange(SM, C.getSourceRange())
-              .str();
-  }
-
-  // Emit body.
-  OS << " ";
-  OS << Lexer::getCharSourceRangeFromSourceRange(
-            SM, InnerIf->getThenStmt()->getSourceRange())
-            .str();
-  return false;
-}
-
 /// Abstract helper class containing info about a TernaryExpr
 /// that can be expanded into an IfStmt.
 class ExpandableTernaryExprInfo {