[flang][runtime] Extension: NAMELIST input may omit terminal '/'

[klausler]

... when it is followed eventually by the '&' that begins the next NAMELIST input group. This is a gfortran extension.

[llvmbot]

@llvm/pr-subscribers-flang-runtime

Author: Peter Klausler (klausler)

Changes

... when it is followed eventually by the '&' that begins the next NAMELIST input group. This is a gfortran extension.

---

Full diff: https://github.com/llvm/llvm-project/pull/76476.diff

2 Files Affected:

• (modified) flang/docs/Extensions.md (+2)
• (modified) flang/runtime/namelist.cpp (+10-6)

diff --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index 6c6588025a392d..eaf85614736a24 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -315,6 +315,8 @@ end
 * When a file included via an `INCLUDE` line or `#include` directive
   has a continuation marker at the end of its last line in free form,
   Fortran line continuation works.
+* A `NAMELIST` input group may omit its trailing `/` character if
+  it is followed by another `NAMELIST` input group.
 
 ### Extensions supported when enabled by options
 
diff --git a/flang/runtime/namelist.cpp b/flang/runtime/namelist.cpp
index 61815a7cc8a403..e714ee1dc76303 100644
--- a/flang/runtime/namelist.cpp
+++ b/flang/runtime/namelist.cpp
@@ -378,12 +378,13 @@ static bool HandleComponent(IoStatementState &io, Descriptor &desc,
   return false;
 }
 
-// Advance to the terminal '/' of a namelist group.
+// Advance to the terminal '/' of a namelist group or leading '&'
+// of the next.
 static void SkipNamelistGroup(IoStatementState &io) {
   std::size_t byteCount{0};
   while (auto ch{io.GetNextNonBlank(byteCount)}) {
     io.HandleRelativePosition(byteCount);
-    if (*ch == '/') {
+    if (*ch == '/' || *ch == '&') {
       break;
     } else if (*ch == '\'' || *ch == '"') {
       // Skip quoted character literal
@@ -448,7 +449,7 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
   // Read the group's items
   while (true) {
     next = io.GetNextNonBlank(byteCount);
-    if (!next || *next == '/') {
+    if (!next || *next == '/' || *next == '&') {
       break;
     }
     if (!GetLowerCaseName(io, name, sizeof name)) {
@@ -540,12 +541,15 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
       io.HandleRelativePosition(byteCount);
     }
   }
-  if (!next || *next != '/') {
+  if (next && *next == '/') {
+    io.HandleRelativePosition(byteCount);
+  } else if (*next && *next == '&') {
+    // stop at beginning of next group
+  } else {
     handler.SignalError(
         "No '/' found after NAMELIST group '%s'", group.groupName);
     return false;
   }
-  io.HandleRelativePosition(byteCount);
   return true;
 }
 
@@ -565,7 +569,7 @@ bool IsNamelistNameOrSlash(IoStatementState &io) {
           // TODO: how to deal with NaN(...) ambiguity?
           return ch && (*ch == '=' || *ch == '(' || *ch == '%');
         } else {
-          return *ch == '/';
+          return *ch == '/' || *ch == '&';
         }
       }
     }