[flang-commits] [flang] [flang] Fix parser crash (PR #105875)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-parser

Author: Peter Klausler (klausler)

<details>
<summary>Changes</summary>

The production for a bare file unit number in an I/O statement checks that the scalar integer expression isn't followed by "=", in order to disambiguate FLUSHN from FLUSHN=1, and to not treat a control specifier keyword as an integer expression.  The implementation of this check used !"="_tok, which has the side effect of producing no error message; this can lead to a parsing crash later when a failed parse of an erroneous program is found to have produced no errors.  Rewrite as a lookAhead call for those characters that acually can follow a bare unit number.

Fixes https://github.com/llvm/llvm-project/issues/105779.

---
Full diff: https://github.com/llvm/llvm-project/pull/105875.diff


2 Files Affected:

- (modified) flang/lib/Parser/io-parsers.cpp (+2-1) 
- (added) flang/test/Parser/recovery05.f90 (+5) 


``````````diff
diff --git a/flang/lib/Parser/io-parsers.cpp b/flang/lib/Parser/io-parsers.cpp
index ca0dbedc8da427..25b09efd40c529 100644
--- a/flang/lib/Parser/io-parsers.cpp
+++ b/flang/lib/Parser/io-parsers.cpp
@@ -27,7 +27,8 @@ TYPE_PARSER(construct<IoUnit>(variable / lookAhead(space / ",);\n"_ch)) ||
     construct<IoUnit>(fileUnitNumber) || construct<IoUnit>(star))
 
 // R1202 file-unit-number -> scalar-int-expr
-TYPE_PARSER(construct<FileUnitNumber>(scalarIntExpr / !"="_tok))
+TYPE_PARSER(construct<FileUnitNumber>(
+    scalarIntExpr / (lookAhead(space >> ",)"_ch) || atEndOfStmt)))
 
 // R1204 open-stmt -> OPEN ( connect-spec-list )
 TYPE_CONTEXT_PARSER("OPEN statement"_en_US,
diff --git a/flang/test/Parser/recovery05.f90 b/flang/test/Parser/recovery05.f90
new file mode 100644
index 00000000000000..9c8c3689b27bd5
--- /dev/null
+++ b/flang/test/Parser/recovery05.f90
@@ -0,0 +1,5 @@
+! RUN: not %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+continue
+! CHECK: error: expected end of statement
+flush iostat=1
+end

``````````

</details>


https://github.com/llvm/llvm-project/pull/105875