From 296040aa960a8b035392d2b66c7bf7faa2ae8ec3 Mon Sep 17 00:00:00 2001
From: peter klausler <pklausler@nvidia.com>
Date: Thu, 12 Jul 2018 16:23:25 -0700
Subject: [PATCH] [flang] Improve error recovery further, using a test case
 from Tim.

Original-commit: flang-compiler/f18@9ef79fa9913804168d151a5b15588dbfaa02957a
Reviewed-on: https://github.com/flang-compiler/f18/pull/123
---
 flang/lib/parser/basic-parsers.h |  2 +-
 flang/lib/parser/grammar.h       | 53 ++++++++++++++++++++--------------------
 flang/lib/parser/type-parsers.h  |  5 +++-
 3 files changed, 32 insertions(+), 28 deletions(-)

diff --git a/flang/lib/parser/basic-parsers.h b/flang/lib/parser/basic-parsers.h
index c1abb08..78d39d7 100644
--- a/flang/lib/parser/basic-parsers.h
+++ b/flang/lib/parser/basic-parsers.h
@@ -208,7 +208,7 @@ public:
 
 private:
   const MessageFixedText text_;
-  const PA parser_;
+  const BacktrackingParser<PA> parser_;
 };
 
 template<typename PA>
diff --git a/flang/lib/parser/grammar.h b/flang/lib/parser/grammar.h
index 37c3817..0c63853 100644
--- a/flang/lib/parser/grammar.h
+++ b/flang/lib/parser/grammar.h
@@ -54,27 +54,27 @@ constexpr auto execPartLookAhead{first(actionStmt >> ok, "ASSOCIATE ("_tok,
     "IF ("_tok, "WHERE ("_tok, "FORALL ("_tok)};
 constexpr auto declErrorRecovery{
     stmtErrorRecoveryStart >> !execPartLookAhead >> stmtErrorRecovery};
-TYPE_CONTEXT_PARSER("declaration construct"_en_US,
-    recovery(
-        withMessage("expected declaration construct"_err_en_US,
+TYPE_PARSER(recovery(
+    withMessage("expected declaration construct"_err_en_US,
+        CONTEXT_PARSER("declaration construct"_en_US,
             first(construct<DeclarationConstruct>(specificationConstruct),
                 construct<DeclarationConstruct>(statement(indirect(dataStmt))),
                 construct<DeclarationConstruct>(
                     statement(indirect(formatStmt))),
                 construct<DeclarationConstruct>(statement(indirect(entryStmt))),
                 construct<DeclarationConstruct>(
-                    statement(indirect(Parser<StmtFunctionStmt>{}))))),
-        construct<DeclarationConstruct>(declErrorRecovery)))
+                    statement(indirect(Parser<StmtFunctionStmt>{})))))),
+    construct<DeclarationConstruct>(declErrorRecovery)))
 
 // R507 variant of declaration-construct for use in limitedSpecificationPart.
-constexpr auto limitedDeclarationConstruct{inContext(
-    "declaration construct"_en_US,
-    recovery(withMessage("expected declaration construct"_err_en_US,
-                 first(construct<DeclarationConstruct>(specificationConstruct),
-                     construct<DeclarationConstruct>(
-                         statement(indirect(dataStmt))))),
-        construct<DeclarationConstruct>(
-            stmtErrorRecoveryStart >> stmtErrorRecovery)))};
+constexpr auto limitedDeclarationConstruct{recovery(
+    withMessage("expected declaration construct"_err_en_US,
+        inContext("declaration construct"_en_US,
+            first(construct<DeclarationConstruct>(specificationConstruct),
+                construct<DeclarationConstruct>(
+                    statement(indirect(dataStmt)))))),
+    construct<DeclarationConstruct>(
+        stmtErrorRecoveryStart >> stmtErrorRecovery))};
 
 // R508 specification-construct ->
 //        derived-type-def | enum-def | generic-stmt | interface-block |
@@ -398,19 +398,20 @@ constexpr auto obsoleteExecutionPartConstruct{recovery(ignoredStatementPrefix >>
             parenthesized(nonemptyList(Parser<AllocateShapeSpec>{})) >> ok) >>
         construct<ErrorRecovery>()))};
 
-TYPE_CONTEXT_PARSER("execution part construct"_en_US,
-    recovery(withMessage("expected execution part construct"_err_en_US,
-                 first(construct<ExecutionPartConstruct>(executableConstruct),
-                     construct<ExecutionPartConstruct>(
-                         statement(indirect(formatStmt))),
-                     construct<ExecutionPartConstruct>(
-                         statement(indirect(entryStmt))),
-                     construct<ExecutionPartConstruct>(
-                         statement(indirect(dataStmt))),
-                     extension(construct<ExecutionPartConstruct>(statement(
-                                   indirect(Parser<NamelistStmt>{}))) ||
-                         obsoleteExecutionPartConstruct))),
-        construct<ExecutionPartConstruct>(executionPartErrorRecovery)))
+TYPE_PARSER(recovery(
+    withMessage("expected execution part construct"_err_en_US,
+        CONTEXT_PARSER("execution part construct"_en_US,
+            first(construct<ExecutionPartConstruct>(executableConstruct),
+                construct<ExecutionPartConstruct>(
+                    statement(indirect(formatStmt))),
+                construct<ExecutionPartConstruct>(
+                    statement(indirect(entryStmt))),
+                construct<ExecutionPartConstruct>(
+                    statement(indirect(dataStmt))),
+                extension(construct<ExecutionPartConstruct>(
+                              statement(indirect(Parser<NamelistStmt>{}))) ||
+                    obsoleteExecutionPartConstruct)))),
+    construct<ExecutionPartConstruct>(executionPartErrorRecovery)))
 
 // R509 execution-part -> executable-construct [execution-part-construct]...
 TYPE_CONTEXT_PARSER("execution part"_en_US,
diff --git a/flang/lib/parser/type-parsers.h b/flang/lib/parser/type-parsers.h
index 428c683..fd3cae1 100644
--- a/flang/lib/parser/type-parsers.h
+++ b/flang/lib/parser/type-parsers.h
@@ -41,8 +41,11 @@ template<typename A> struct Parser {
     return parser.Parse(state); \
   }
 
+#define CONTEXT_PARSER(contextText, pexpr) \
+  instrumented((contextText), inContext((contextText), (pexpr)))
+
 #define TYPE_CONTEXT_PARSER(contextText, pexpr) \
-  TYPE_PARSER(instrumented((contextText), inContext((contextText), (pexpr))))
+  TYPE_PARSER(CONTEXT_PARSER((contextText), (pexpr)))
 
 // Some specializations of Parser<> are used multiple times, or are
 // of some special importance, so we instantiate them once here and
-- 
2.7.4