[flang-commits] [flang] [Flang] Give a more specific error message for expressions where an IO Unit is expected (PR #126970)

[Peter Klausler via flang-commits]

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@@ -23,8 +23,12 @@ namespace Fortran::parser {
 // R905 char-variable -> variable
 // "char-variable" is attempted first since it's not type constrained but
 // syntactically ambiguous with "file-unit-number", which is constrained.
+// Note, "file-unit-number" is replaced by "expr" to allow for better
+// error messages.
 TYPE_PARSER(construct<IoUnit>(variable / lookAhead(space / ",);\n"_ch)) ||
-    construct<IoUnit>(fileUnitNumber) || construct<IoUnit>(star))
+    construct<IoUnit>(
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klausler wrote:

Would not the other uses of `fileUnitNumber` in this file also benefit from this change?  If so, consider modifying the parser for `FileUnitNumber` itself.

https://github.com/llvm/llvm-project/pull/126970