[Parser]: Labeled block without do diagnostics (swiftlang#29147)

Improve diagnostics for labeled block without 'do'.
Parse and diagnose { identifier ':' '{' } as a labeled 'do' statement.

https://bugs.swift.org/browse/SR-3867

Author: kitaisreal

include/swift/AST/DiagnosticsParse.def

@@ -933,6 +933,8 @@ ERROR(statement_same_line_without_semi,none,
       "consecutive statements on a line must be separated by ';'", ())
 ERROR(invalid_label_on_stmt,none,
       "labels are only valid on loops, if, and switch statements", ())
+ERROR(labeled_block_needs_do,none,
+      "labeled block needs 'do'", ())
 
 ERROR(snake_case_deprecated,none,
       "%0 has been replaced with %1 in Swift 3",

include/swift/Parse/Parser.h

@@ -1603,7 +1603,8 @@ class Parser {
   ParserResult<Stmt> parseStmtGuard();
   ParserResult<Stmt> parseStmtWhile(LabeledStmtInfo LabelInfo);
   ParserResult<Stmt> parseStmtRepeat(LabeledStmtInfo LabelInfo);
-  ParserResult<Stmt> parseStmtDo(LabeledStmtInfo LabelInfo);
+  ParserResult<Stmt> parseStmtDo(LabeledStmtInfo LabelInfo,
+                                 bool shouldSkipDoTokenConsume = false);
   ParserResult<CatchStmt> parseStmtCatch();
   ParserResult<Stmt> parseStmtForEach(LabeledStmtInfo LabelInfo);
   ParserResult<Stmt> parseStmtSwitch(LabeledStmtInfo LabelInfo);

lib/Parse/ParseStmt.cpp

@@ -93,6 +93,12 @@ bool Parser::isStartOfStmt() {
     Parser::BacktrackingScope backtrack(*this);
     consumeToken(tok::identifier);
     consumeToken(tok::colon);
+
+    // We treating IDENTIIFIER: { as start of statement to provide missed 'do'
+    // diagnostics. This case will be handled in parseStmt().
+    if (Tok.is(tok::l_brace)) {
+      return true;
+    }
     // For better recovery, we just accept a label on any statement.  We reject
     // putting a label on something inappropriate in parseStmt().
     return isStartOfStmt();
@@ -637,6 +643,12 @@ ParserResult<Stmt> Parser::parseStmt() {
     if (LabelInfo) diagnose(LabelInfo.Loc, diag::invalid_label_on_stmt);
     if (tryLoc.isValid()) diagnose(tryLoc, diag::try_on_stmt, Tok.getText());
     return parseStmtPoundAssert();
+  case tok::l_brace:
+    if (tryLoc.isValid()) diagnose(tryLoc, diag::try_on_stmt, Tok.getText());
+    SourceLoc colonLoc = Tok.getLoc();
+    diagnose(colonLoc, diag::labeled_block_needs_do)
+      .fixItInsert(colonLoc, "do ");
+    return parseStmtDo(LabelInfo, /*shouldSkipDoTokenConsume*/ true);
   }
 }
 
@@ -1875,9 +1887,16 @@ ParserResult<Stmt> Parser::parseStmtRepeat(LabeledStmtInfo labelInfo) {
 ///   stmt-do:
 ///     (identifier ':')? 'do' stmt-brace
 ///     (identifier ':')? 'do' stmt-brace stmt-catch+
-ParserResult<Stmt> Parser::parseStmtDo(LabeledStmtInfo labelInfo) {
+ParserResult<Stmt> Parser::parseStmtDo(LabeledStmtInfo labelInfo,
+                                       bool shouldSkipDoTokenConsume) {
   SyntaxContext->setCreateSyntax(SyntaxKind::DoStmt);
-  SourceLoc doLoc = consumeToken(tok::kw_do);
+  SourceLoc doLoc;
+
+  if (shouldSkipDoTokenConsume) {
+    doLoc = Tok.getLoc();
+  } else {
+    doLoc = consumeToken(tok::kw_do);
+  }
 
   ParserStatus status;
 

test/stmt/statements.swift

@@ -252,6 +252,11 @@ func DoWhileStmt2() {
   }
 }
 
+func LabeledDoStmt() {
+  LABEL: { // expected-error {{labeled block needs 'do'}} {{10-10=do }}
+  }
+}
+
 //===--- Repeat-while statement.
 
 func RepeatWhileStmt1() {