[Parse] getLineNumber before parsing the closure (#15178)

Previously, if the closure has nested trailing closure, it slows down
because of cache in SourceMgr.

Author: rintaro

lib/Parse/ParseExpr.cpp

@@ -3089,6 +3089,12 @@ ParserStatus Parser::parseExprList(tok leftTok, tok rightTok,
 ParserResult<Expr> Parser::parseTrailingClosure(SourceRange calleeRange) {
   SourceLoc braceLoc = Tok.getLoc();
 
+  // Record the line numbers for the diagnostics below.
+  // Note that *do not* move this to after 'parseExprClosure()' it slows down
+  // 'getLineNumber()' call because of cache in SourceMgr.
+  auto origLine = SourceMgr.getLineNumber(calleeRange.End);
+  auto braceLine = SourceMgr.getLineNumber(braceLoc);
+
   // Parse the closure.
   ParserResult<Expr> closure = parseExprClosure();
   if (closure.isNull())
@@ -3097,8 +3103,6 @@ ParserResult<Expr> Parser::parseTrailingClosure(SourceRange calleeRange) {
   // Warn if the trailing closure is separated from its callee by more than
   // one line. A single-line separation is acceptable for a trailing closure
   // call, and will be diagnosed later only if the call fails to typecheck.
-  auto origLine = SourceMgr.getLineNumber(calleeRange.End);
-  auto braceLine = SourceMgr.getLineNumber(braceLoc);
   if (braceLine > origLine + 1) {
     diagnose(braceLoc, diag::trailing_closure_after_newlines);
     diagnose(calleeRange.Start, diag::trailing_closure_callee_here);