[flang] Fix repeated "DT" editing

User-defined derived type editing in formatted I/O wasn't
working with repeat counts; e.g., "2DT(10)".  The solution required
some code to be moved from GetNextDataEdit() to CueUpNextDataEdit() so
that a stack entry for a nonparenthesized repeated data edit
descriptor would work correctly -- all other data edit descriptors
are capable of dealing with repetition in their callees, so the bug
hadn't been exposed before.

Debugging this problem led to some improvements in error messages
for bad format strings, and those changes have been retained; also,
a dead member function was discovered and expunged.

Differential Revision: https://reviews.llvm.org/D117904

4 files changed, 55 insertions, 101 deletions

diff --git a/flang/runtime/descriptor-io.cpp b/flang/runtime/descriptor-io.cpp
index 20828a6d9a84..d34ac68c8a53 100644
--- a/flang/runtime/descriptor-io.cpp
+++ b/flang/runtime/descriptor-io.cpp
@@ -19,7 +19,7 @@ std::optional<bool> DefinedFormattedIo(IoStatementState &io,
           peek->descriptor == DataEdit::ListDirected)) {
     // User-defined derived type formatting
     IoErrorHandler &handler{io.GetIoErrorHandler()};
-    DataEdit edit{*io.GetNextDataEdit()}; // consume it this time
+    DataEdit edit{*io.GetNextDataEdit(1)}; // now consume it; no repeats
     RUNTIME_CHECK(handler, edit.descriptor == peek->descriptor);
     char ioType[2 + edit.maxIoTypeChars];
     auto ioTypeLen{std::size_t{2} /*"DT"*/ + edit.ioTypeChars};
diff --git a/flang/runtime/format-implementation.h b/flang/runtime/format-implementation.h
index a32bb8e928fd..b9c1b8427afe 100644
--- a/flang/runtime/format-implementation.h
+++ b/flang/runtime/format-implementation.h
@@ -34,59 +34,6 @@ FormatControl<CONTEXT>::FormatControl(const Terminator &terminator,
 }
 
 template <typename CONTEXT>
-int FormatControl<CONTEXT>::GetMaxParenthesisNesting(
-    IoErrorHandler &handler, const CharType *format, std::size_t formatLength) {
-  int maxNesting{0};
-  int nesting{0};
-  const CharType *end{format + formatLength};
-  std::optional<CharType> quote;
-  int repeat{0};
-  for (const CharType *p{format}; p < end; ++p) {
-    if (quote) {
-      if (*p == *quote) {
-        quote.reset();
-      }
-    } else if (*p >= '0' && *p <= '9') {
-      repeat = 10 * repeat + *p - '0';
-    } else if (*p != ' ') {
-      switch (*p) {
-      case '\'':
-      case '"':
-        quote = *p;
-        break;
-      case 'h':
-      case 'H': // 9HHOLLERITH
-        p += repeat;
-        if (p >= end) {
-          handler.SignalError(IostatErrorInFormat,
-              "Hollerith (%dH) too long in FORMAT", repeat);
-          return maxNesting;
-        }
-        break;
-      case ' ':
-        break;
-      case '(':
-        ++nesting;
-        maxNesting = std::max(nesting, maxNesting);
-        break;
-      case ')':
-        nesting = std::max(nesting - 1, 0);
-        break;
-      }
-      repeat = 0;
-    }
-  }
-  if (quote) {
-    handler.SignalError(
-        IostatErrorInFormat, "Unbalanced quotation marks in FORMAT string");
-  } else if (nesting) {
-    handler.SignalError(
-        IostatErrorInFormat, "Unbalanced parentheses in FORMAT string");
-  }
-  return maxNesting;
-}
-
-template <typename CONTEXT>
 int FormatControl<CONTEXT>::GetIntField(
     IoErrorHandler &handler, CharType firstCh) {
   CharType ch{firstCh ? firstCh : PeekNext()};
@@ -98,7 +45,11 @@ int FormatControl<CONTEXT>::GetIntField(
   int result{0};
   bool negate{ch == '-'};
   if (negate || ch == '+') {
-    firstCh = '\0';
+    if (firstCh) {
+      firstCh = '\0';
+    } else {
+      ++offset_;
+    }
     ch = PeekNext();
   }
   while (ch >= '0' && ch <= '9') {
@@ -222,6 +173,15 @@ static void HandleControl(CONTEXT &context, char ch, char next, int n) {
 template <typename CONTEXT>
 int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
   int unlimitedLoopCheck{-1};
+  // Do repetitions remain on an unparenthesized data edit?
+  while (height_ > 1 && format_[stack_[height_ - 1].start] != '(') {
+    offset_ = stack_[height_ - 1].start;
+    int repeat{stack_[height_ - 1].remaining};
+    --height_;
+    if (repeat > 0) {
+      return repeat;
+    }
+  }
   while (true) {
     std::optional<int> repeat;
     bool unlimited{false};
@@ -242,16 +202,18 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
       unlimited = true;
       ch = GetNextChar(context);
       if (ch != '(') {
-        context.SignalError(IostatErrorInFormat,
-            "Invalid FORMAT: '*' may appear only before '('");
+        ReportBadFormat(context,
+            "Invalid FORMAT: '*' may appear only before '('",
+            maybeReversionPoint);
         return 0;
       }
     }
     ch = Capitalize(ch);
     if (ch == '(') {
       if (height_ >= maxHeight_) {
-        context.SignalError(IostatErrorInFormat,
-            "FORMAT stack overflow: too many nested parentheses");
+        ReportBadFormat(context,
+            "FORMAT stack overflow: too many nested parentheses",
+            maybeReversionPoint);
         return 0;
       }
       stack_[height_].start = offset_ - 1; // the '('
@@ -271,11 +233,11 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
         // Subtle point (F'2018 13.4 para 9): tha last parenthesized group
         // at height 1 becomes the restart point after control reaches the
         // end of the format, including its repeat count.
-        stack_[0].start = maybeReversionPoint - 1;
+        stack_[0].start = maybeReversionPoint;
       }
       ++height_;
     } else if (height_ == 0) {
-      context.SignalError(IostatErrorInFormat, "FORMAT lacks initial '('");
+      ReportBadFormat(context, "FORMAT lacks initial '('", maybeReversionPoint);
       return 0;
     } else if (ch == ')') {
       if (height_ == 1) {
@@ -284,12 +246,16 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
         }
         context.AdvanceRecord(); // implied / before rightmost )
       }
-      auto restart{stack_[height_ - 1].start + 1};
+      auto restart{stack_[height_ - 1].start};
+      if (format_[restart] == '(') {
+        ++restart;
+      }
       if (stack_[height_ - 1].remaining == Iteration::unlimited) {
         offset_ = restart;
         if (offset_ == unlimitedLoopCheck) {
-          context.SignalError(IostatErrorInFormat,
-              "Unlimited repetition in FORMAT lacks data edit descriptors");
+          ReportBadFormat(context,
+              "Unlimited repetition in FORMAT lacks data edit descriptors",
+              restart);
         }
       } else if (stack_[height_ - 1].remaining-- > 0) {
         offset_ = restart;
@@ -304,8 +270,9 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
         ++offset_;
       }
       if (offset_ >= formatLength_) {
-        context.SignalError(IostatErrorInFormat,
-            "FORMAT missing closing quote on character literal");
+        ReportBadFormat(context,
+            "FORMAT missing closing quote on character literal",
+            maybeReversionPoint);
         return 0;
       }
       ++offset_;
@@ -322,8 +289,8 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
     } else if (ch == 'H') {
       // 9HHOLLERITH
       if (!repeat || *repeat < 1 || offset_ + *repeat > formatLength_) {
-        context.SignalError(
-            IostatErrorInFormat, "Invalid width on Hollerith in FORMAT");
+        ReportBadFormat(context, "Invalid width on Hollerith in FORMAT",
+            maybeReversionPoint);
         return 0;
       }
       context.Emit(format_ + offset_, static_cast<std::size_t>(*repeat));
@@ -364,8 +331,8 @@ int FormatControl<CONTEXT>::CueUpNextDataEdit(Context &context, bool stop) {
       // TODO: any other raw characters?
       context.Emit(format_ + offset_ - 1, 1);
     } else {
-      context.SignalError(IostatErrorInFormat,
-          "Invalid character '%c' in FORMAT", static_cast<char>(ch));
+      ReportBadFormat(
+          context, "Invalid character in FORMAT", maybeReversionPoint);
       return 0;
     }
   }
@@ -410,11 +377,9 @@ DataEdit FormatControl<CONTEXT>::GetNextDataEdit(
         }
       }
       if (!ok) {
-        context.SignalError(
-            IostatErrorInFormat, "Unclosed DT'iotype' in FORMAT");
+        ReportBadFormat(context, "Unclosed DT'iotype' in FORMAT", start);
       } else if (tooLong) {
-        context.SignalError(
-            IostatErrorInFormat, "Excessive DT'iotype' in FORMAT");
+        ReportBadFormat(context, "Excessive DT'iotype' in FORMAT", start);
       }
     }
     if (PeekNext() == '(') {
@@ -434,11 +399,9 @@ DataEdit FormatControl<CONTEXT>::GetNextDataEdit(
         }
       }
       if (!ok) {
-        context.SignalError(
-            IostatErrorInFormat, "Unclosed DT(v_list) in FORMAT");
+        ReportBadFormat(context, "Unclosed DT(v_list) in FORMAT", start);
       } else if (tooLong) {
-        context.SignalError(
-            IostatErrorInFormat, "Excessive DT(v_list) in FORMAT");
+        ReportBadFormat(context, "Excessive DT(v_list) in FORMAT", start);
       }
     }
   }
@@ -460,27 +423,13 @@ DataEdit FormatControl<CONTEXT>::GetNextDataEdit(
     }
   }
   edit.modes = context.mutableModes();
-
   // Handle repeated nonparenthesized edit descriptors
+  edit.repeat = std::min(repeat, maxRepeat); // 0 if maxRepeat==0
   if (repeat > maxRepeat) {
     stack_[height_].start = start; // after repeat count
-    stack_[height_].remaining = repeat; // full count
+    stack_[height_].remaining = repeat - edit.repeat;
     ++height_;
   }
-  edit.repeat = std::min(1, maxRepeat); // 0 if maxRepeat==0
-  if (height_ > 1) { // Subtle: stack_[0].start doesn't necessarily point to '('
-    int start{stack_[height_ - 1].start};
-    if (format_[start] != '(') {
-      if (stack_[height_ - 1].remaining > maxRepeat) {
-        edit.repeat = maxRepeat;
-        stack_[height_ - 1].remaining -= maxRepeat;
-        offset_ = start; // repeat same edit descriptor next time
-      } else {
-        edit.repeat = stack_[height_ - 1].remaining;
-        --height_;
-      }
-    }
-  }
   return edit;
 }
 
diff --git a/flang/runtime/format.h b/flang/runtime/format.h
index 8dccaab969a6..98c1136b0f51 100644
--- a/flang/runtime/format.h
+++ b/flang/runtime/format.h
@@ -86,11 +86,6 @@ public:
   FormatControl(const Terminator &, const CharType *format,
       std::size_t formatLength, int maxHeight = maxMaxHeight);
 
-  // Determines the max parenthesis nesting level by scanning and validating
-  // the FORMAT string.
-  static int GetMaxParenthesisNesting(
-      IoErrorHandler &, const CharType *format, std::size_t formatLength);
-
   // For attempting to allocate in a user-supplied stack area
   static std::size_t GetNeededSize(int maxHeight) {
     return sizeof(FormatControl) -
@@ -146,6 +141,15 @@ private:
     return ch >= 'a' && ch <= 'z' ? ch + 'A' - 'a' : ch;
   }
 
+  void ReportBadFormat(Context &context, const char *msg, int offset) const {
+    if constexpr (std::is_same_v<CharType, char>) {
+      context.SignalError(IostatErrorInFormat,
+          "%s; at offset %d in format '%s'", msg, offset, format_);
+    } else {
+      context.SignalError(IostatErrorInFormat, "%s; at offset %d", msg, offset);
+    }
+  }
+
   // Data members are arranged and typed so as to reduce size.
   // This structure may be allocated in stack space loaned by the
   // user program for internal I/O.
diff --git a/flang/runtime/io-stmt.h b/flang/runtime/io-stmt.h
index 8327326c7f9e..baf038dbdd24 100644
--- a/flang/runtime/io-stmt.h
+++ b/flang/runtime/io-stmt.h
@@ -87,7 +87,7 @@ public:
   void BackspaceRecord();
   void HandleRelativePosition(std::int64_t);
   void HandleAbsolutePosition(std::int64_t); // for r* in list I/O
-  std::optional<DataEdit> GetNextDataEdit(int = 1);
+  std::optional<DataEdit> GetNextDataEdit(int maxRepeat = 1);
   ExternalFileUnit *GetExternalFileUnit() const; // null if internal unit
   bool BeginReadingRecord();
   void FinishReadingRecord();
@@ -287,7 +287,8 @@ struct IoStatementBase : public IoErrorHandler {
   void BackspaceRecord();
   void HandleRelativePosition(std::int64_t);
   void HandleAbsolutePosition(std::int64_t);
-  std::optional<DataEdit> GetNextDataEdit(IoStatementState &, int = 1);
+  std::optional<DataEdit> GetNextDataEdit(
+      IoStatementState &, int maxRepeat = 1);
   ExternalFileUnit *GetExternalFileUnit() const;
   bool BeginReadingRecord();
   void FinishReadingRecord();