[flang][runtime] Extension: NAMELIST input may omit terminal '/' (#76476)

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

Author: klausler

flang/docs/Extensions.md

@@ -315,6 +315,9 @@ 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.
+* A `NAMELIST` input group may begin with either `&` or `$`.
 
 ### Extensions supported when enabled by options
 

flang/runtime/edit-input.cpp

@@ -21,7 +21,8 @@ namespace Fortran::runtime::io {
 static inline bool IsCharValueSeparator(const DataEdit &edit, char32_t ch) {
   char32_t comma{
       edit.modes.editingFlags & decimalComma ? char32_t{';'} : char32_t{','}};
-  return ch == ' ' || ch == '\t' || ch == '/' || ch == comma;
+  return ch == ' ' || ch == '\t' || ch == comma || ch == '/' ||
+      (edit.IsNamelist() && (ch == '&' || ch == '$'));
 }
 
 static bool CheckCompleteListDirectedField(
@@ -917,6 +918,10 @@ static bool EditListDirectedCharacterInput(
     case '/':
       isSep = true;
       break;
+    case '&':
+    case '$':
+      isSep = edit.IsNamelist();
+      break;
     case ',':
       isSep = !(edit.modes.editingFlags & decimalComma);
       break;

flang/runtime/io-stmt.cpp

@@ -580,6 +580,12 @@ std::optional<char32_t> IoStatementState::NextInField(
         case '*':
         case '\n': // for stream access
           return std::nullopt;
+        case '&':
+        case '$':
+          if (edit.IsNamelist()) {
+            return std::nullopt;
+          }
+          break;
         case ',':
           if (!(edit.modes.editingFlags & decimalComma)) {
             return std::nullopt;

flang/runtime/namelist.cpp

@@ -82,7 +82,7 @@ bool IONAME(OutputNamelist)(Cookie cookie, const NamelistGroup &group) {
 
 static constexpr bool IsLegalIdStart(char32_t ch) {
   return (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z') || ch == '_' ||
-      ch == '@' || ch == '$';
+      ch == '@';
 }
 
 static constexpr bool IsLegalIdChar(char32_t ch) {
@@ -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 '&'/'$'
+// of the next.
 static void SkipNamelistGroup(IoStatementState &io) {
   std::size_t byteCount{0};
   while (auto ch{io.GetNextNonBlank(byteCount)}) {
     io.HandleRelativePosition(byteCount);
-    if (*ch == '/') {
+    if (*ch == '/' || *ch == '&' || *ch == '$') {
       break;
     } else if (*ch == '\'' || *ch == '"') {
       // Skip quoted character literal
@@ -418,7 +419,7 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
   std::size_t byteCount{0};
   while (true) {
     next = io.GetNextNonBlank(byteCount);
-    while (next && *next != '&') {
+    while (next && *next != '&' && *next != '$') {
       // Extension: comment lines without ! before namelist groups
       if (!io.AdvanceRecord()) {
         next.reset();
@@ -430,9 +431,10 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
       handler.SignalEnd();
       return false;
     }
-    if (*next != '&') {
+    if (*next != '&' && *next != '$') {
       handler.SignalError(
-          "NAMELIST input group does not begin with '&' (at '%lc')", *next);
+          "NAMELIST input group does not begin with '&' or '$' (at '%lc')",
+          *next);
       return false;
     }
     io.HandleRelativePosition(byteCount);
@@ -448,7 +450,7 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
   // Read the group's items
   while (true) {
     next = io.GetNextNonBlank(byteCount);
-    if (!next || *next == '/') {
+    if (!next || *next == '/' || *next == '&' || *next == '$') {
       break;
     }
     if (!GetLowerCaseName(io, name, sizeof name)) {
@@ -540,12 +542,15 @@ bool IONAME(InputNamelist)(Cookie cookie, const NamelistGroup &group) {
       io.HandleRelativePosition(byteCount);
     }
   }
-  if (!next || *next != '/') {
+  if (next && *next == '/') {
+    io.HandleRelativePosition(byteCount);
+  } else if (*next && (*next == '&' || *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 +570,7 @@ bool IsNamelistNameOrSlash(IoStatementState &io) {
           // TODO: how to deal with NaN(...) ambiguity?
           return ch && (*ch == '=' || *ch == '(' || *ch == '%');
         } else {
-          return *ch == '/';
+          return *ch == '/' || *ch == '&' || *ch == '$';
         }
       }
     }