[flang] Catch I/O statement error (#116647)

Fortran doesn't have unformatted internal I/O, so catch attempts to use
internal units without a format or namelist specifier.

Fixes #116586.

Author: klausler

flang/lib/Semantics/check-io.cpp

@@ -860,6 +860,8 @@ void IoChecker::Leave(const parser::WriteStmt &writeStmt) {
 
 void IoChecker::LeaveReadWrite() const {
   CheckForRequiredSpecifier(IoSpecKind::Unit); // C1211
+  CheckForRequiredSpecifier(flags_.test(Flag::InternalUnit),
+      "UNIT=internal-file", flags_.test(Flag::FmtOrNml), "FMT or NML");
   CheckForProhibitedSpecifier(IoSpecKind::Nml, IoSpecKind::Rec); // C1216
   CheckForProhibitedSpecifier(IoSpecKind::Nml, IoSpecKind::Fmt); // C1216
   CheckForProhibitedSpecifier(

flang/test/Semantics/io03.f90

@@ -58,6 +58,13 @@
   read(internal_file2, *) jj
   read(internal_file4, *) jj
 
+  !This is a valid statement but it's not what it looks like; "(internal-file)"
+  !must be parsed as a format expression, not as an internal unit.
+  read(internal_file) jj
+
+  !ERROR: If UNIT=internal-file appears, FMT or NML must also appear
+  read(internal_file, iostat=stat1) jj
+
   !ERROR: Internal file must not have a vector subscript
   read(internal_fileA(vv), *) jj
 
@@ -106,11 +113,12 @@
   !ERROR: If UNIT=* appears, POS must not appear
   read(*, pos=13)
 
+  !ERROR: If UNIT=internal-file appears, FMT or NML must also appear
   !ERROR: If UNIT=internal-file appears, REC must not appear
   read(internal_file, rec=13)
 
   !ERROR: If UNIT=internal-file appears, POS must not appear
-  read(internal_file, pos=13)
+  read(internal_file, *, pos=13)
 
   !ERROR: If REC appears, END must not appear
   read(10, fmt='(I4)', end=9, rec=13) jj
@@ -135,7 +143,7 @@
   read(*, asynchronous='yes')
 
   !ERROR: If ASYNCHRONOUS='YES' appears, UNIT=number must also appear
-  read(internal_file, asynchronous='y'//'es')
+  read(internal_file, *, asynchronous='y'//'es')
 
   !ERROR: If ID appears, ASYNCHRONOUS='YES' must also appear
   read(10, id=id)

flang/test/Semantics/io04.f90

@@ -34,6 +34,7 @@
   write(unit=10) 'Ok'
   write(*, nnn)
   write(10, nnn)
+  !ERROR: If UNIT=internal-file appears, FMT or NML must also appear
   write(internal_file)
   write(internal_file, *)
   write(internal_file, fmt=*)
@@ -55,7 +56,7 @@
   allocate(a(8), stat=stat8)
 
   !ERROR: Duplicate UNIT specifier
-  write(internal_file, unit=*)
+  write(internal_file, unit=*, fmt=*)
 
   !ERROR: WRITE statement must have a UNIT specifier
   write(nml=nnn)
@@ -84,6 +85,7 @@
   !ERROR: If UNIT=internal-file appears, POS must not appear
   write(internal_file, err=9, pos=n, nml=nnn)
 
+  !ERROR: If UNIT=internal-file appears, FMT or NML must also appear
   !ERROR: If UNIT=internal-file appears, REC must not appear
   write(internal_file, rec=n, err=9)
 
@@ -106,7 +108,7 @@
   write(*, asynchronous='yes')
 
   !ERROR: If ASYNCHRONOUS='YES' appears, UNIT=number must also appear
-  write(internal_file, asynchronous='yes')
+  write(internal_file, *, asynchronous='yes')
 
   !ERROR: If ID appears, ASYNCHRONOUS='YES' must also appear
   write(10, *, id=id) "Ok"

flang/test/Semantics/undef-result01.f90

@@ -117,7 +117,7 @@ function defdByNamelist()
 end
 
 character(4) function defdByWrite()
-  write(defdByWrite) 'abcd'
+  write(defdByWrite,*) 'abcd'
 end
 
 integer function defdBySize()