[flang] Relax the implementation of constraint C1302. (flang-compiler/f18#805)

* Relax the implementation of constraint C1302.

When a list of format items can be unambiguously partitioned into individual items even though one or more otherwise required comma separators are omitted, generate a warning rather than an error.

Fixes flang-compiler/f18#703

Original-commit: flang-compiler/f18@79c0731137
Reviewed-on: https://github.com/flang-compiler/f18/pull/805

flang/lib/common/format.h

@@ -16,6 +16,7 @@
 #define FORTRAN_COMMON_FORMAT_H_
 
 #include "Fortran.h"
+#include "enum-set.h"
 #include <cstring>
 
 // Define a FormatValidator class template to validate a format expression
@@ -41,6 +42,16 @@ struct FormatMessage {
   bool isError;  // vs. warning
 };
 
+// This declaration is logically private to class FormatValidator.
+// It is placed here to work around a clang compilation problem.
+ENUM_CLASS(TokenKind, None, A, B, BN, BZ, D, DC, DP, DT, E, EN, ES, EX, F, G, I,
+    L, O, P, RC, RD, RN, RP, RU, RZ, S, SP, SS, T, TL, TR, X, Z, Colon, Slash,
+    Backslash,  // nonstandard: inhibit newline on output
+    Dollar,  // nonstandard: inhibit newline on output on terminals
+    Star, LParen, RParen, Comma, Point, Sign,
+    UnsignedInteger,  // value in integerValue_
+    String)  // char-literal-constant or Hollerith constant
+
 template<typename CHAR = char> class FormatValidator {
 public:
   using Reporter = std::function<bool(const FormatMessage &)>;
@@ -54,53 +65,11 @@ public:
   bool Check();
 
 private:
-  enum class TokenKind {
-    None,
-    A,
-    B,
-    BN,
-    BZ,
-    D,
-    DC,
-    DP,
-    DT,
-    E,
-    EN,
-    ES,
-    EX,
-    F,
-    G,
-    I,
-    L,
-    O,
-    P,
-    RC,
-    RD,
-    RN,
-    RP,
-    RU,
-    RZ,
-    S,
-    SP,
-    SS,
-    T,
-    TL,
-    TR,
-    X,
-    Z,
-    Colon,
-    Slash,
-    Backslash,  // nonstandard: inhibit newline on output
-    Dollar,  // nonstandard: inhibit newline on output on terminals
-    Star,
-    LParen,
-    RParen,
-    Comma,
-    Point,
-    Sign,
-    UnsignedInteger,  // value in integerValue_
-    String,  // char-literal-constant or Hollerith constant
-  };
+  common::EnumSet<TokenKind, TokenKind_enumSize> itemsWithLeadingInts_{
+      TokenKind::A, TokenKind::B, TokenKind::D, TokenKind::DT, TokenKind::E,
+      TokenKind::EN, TokenKind::ES, TokenKind::EX, TokenKind::F, TokenKind::G,
+      TokenKind::I, TokenKind::L, TokenKind::O, TokenKind::P, TokenKind::X,
+      TokenKind::Z, TokenKind::Slash, TokenKind::LParen};
 
   struct Token {
     Token &set_kind(TokenKind kind) {
@@ -176,6 +145,7 @@ private:
   Token knrToken_{};  // k, n, or r UnsignedInteger token
   int64_t knrValue_{-1};  // -1 ==> not present
   int64_t wValue_{-1};
+  bool previousTokenWasInt_{false};
   char argString_[3]{};  // 1-2 character msg arg; usually edit descriptor name
   bool formatHasErrors_{false};
   bool unterminatedFormatError_{false};
@@ -213,6 +183,7 @@ template<typename CHAR> void FormatValidator<CHAR>::NextToken() {
   // At entry, cursor_ points before the start of the next token.
   // At exit, cursor_ points to last CHAR of token_.
 
+  previousTokenWasInt_ = token_.kind() == TokenKind::UnsignedInteger;
   CHAR c{NextChar()};
   token_.set_kind(TokenKind::None);
   token_.set_offset(cursor_ - format_);
@@ -472,7 +443,7 @@ template<typename CHAR> bool FormatValidator<CHAR>::Check() {
   Token starToken{};  // unlimited format token
   bool hasDataEditDesc{false};
 
-  // Subject to error recovery exceptions, a loop iteration processes an
+  // Subject to error recovery exceptions, a loop iteration processes one
   // edit descriptor or does list management.  The loop terminates when
   //  - a level-0 right paren is processed (format may be valid)
   //  - the end of an incomplete format is reached
@@ -773,7 +744,12 @@ template<typename CHAR> bool FormatValidator<CHAR>::Check() {
     default:
       // Possible first token of the next format item; token not yet processed.
       if (commaRequired) {
-        ReportError("Expected ',' or ')' in format expression");  // C1302
+        const char *s{"Expected ',' or ')' in format expression"};  // C1302
+        if (previousTokenWasInt_ && itemsWithLeadingInts_.test(token_.kind())) {
+          ReportError(s);
+        } else {
+          ReportWarning(s);
+        }
       }
     }
   }

flang/test/semantics/io07.f90

@@ -30,6 +30,12 @@
 2011 format(:2L2)
 2012 format(2L2 : 2L2)
 
+     ! C1302 warnings; no errors
+2051 format(1X3/)
+2052 format(1X003/)
+2053 format(3P7I2)
+2054 format(3PI2)
+
      !ERROR: Expected ',' or ')' in format expression
 2101 format(3I83Z8, 'abc')
 
@@ -42,18 +48,6 @@
      !ERROR: Expected ',' or ')' in format expression
 2104 format(3I8 Z8)
 
-     !ERROR: Expected ',' or ')' in format expression
-2105 format(1X3/)
-
-     !ERROR: Expected ',' or ')' in format expression
-2106 format(1X003/)
-
-     !ERROR: Expected ',' or ')' in format expression
-2107 format(3P7I2)
-
-     !ERROR: Expected ',' or ')' in format expression
-2108 format(3PI2)
-
 3001 format(*(I3))
 3002 format(5X,*(2(A)))
 

flang/test/semantics/io08.f90

@@ -51,6 +51,11 @@
   write(*,'(\)')
   write(*,'(RZ,RU,RP,RN,RD,RC,SS,SP,S,3G15.3e2)')
 
+  ! C1302 warnings; no errors
+  write(*,'(3P7I2)')
+  write(*,'(5X i3)')
+  write(*,'(XEN)')
+
   !ERROR: Empty format expression
   write(*,"")
 
@@ -72,12 +77,6 @@
   !ERROR: 'P' edit descriptor must have a scale factor
   write(*,'(P7F' // '5.2)')
 
-  !ERROR: Expected ',' or ')' in format expression
-  write(*,'(3P7I2)')
-
-  !ERROR: Expected ',' or ')' in format expression
-  write(*,'(5X i3)')
-
   !ERROR: Unexpected integer constant
   write(*,'(X,3,3L4)')
 
@@ -186,9 +185,6 @@
   !ERROR: Unexpected 'M' in format expression
   write(*,'(MXY)')
 
-  !ERROR: Expected ',' or ')' in format expression
-  write(*,'(XEN)')
-
   !ERROR: Unexpected 'R' in format expression
   !ERROR: Unexpected 'R' in format expression
   write(*,"(RR, RV)")
@@ -265,9 +261,8 @@
   !ERROR: Unterminated format expression
   write(*,'(X')
 
-  !ERROR: Expected ',' or ')' in format expression
   !ERROR: Unterminated format expression
-  write(*,'(XX')
+  write(*,'(XX') ! C1302 warning is not an error
 
   !ERROR: Unexpected '@' in format expression
   !ERROR: Unexpected '#' in format expression

flang/test/semantics/io10.f90

@@ -35,4 +35,18 @@
 
   !WARNING: Legacy 'H' edit descriptor
   write(*, '(3Habc)')
+
+  !WARNING: 'X' edit descriptor must have a positive position value
+  !WARNING: Expected ',' or ')' in format expression
+  !WARNING: 'X' edit descriptor must have a positive position value
+  write(*,'(XX)')
+
+  !WARNING: Expected ',' or ')' in format expression
+  write(*,'(RZEN8.2)')
+
+  !WARNING: Expected ',' or ')' in format expression
+  write(*,'(3P7I2)')
+
+  !WARNING: Expected ',' or ')' in format expression
+  write(*,'(5X i3)')
 end