[flang-commits] [flang] 28eec1b - [flang] Portability warning and documentation for an obscure extension

[Peter Klausler via flang-commits]

Author: Peter Klausler
Date: 2023-07-21T14:30:40-07:00
New Revision: 28eec1bd85d2a0eb342fbad8fb2cace389e772d5

URL: https://github.com/llvm/llvm-project/commit/28eec1bd85d2a0eb342fbad8fb2cace389e772d5
DIFF: https://github.com/llvm/llvm-project/commit/28eec1bd85d2a0eb342fbad8fb2cace389e772d5.diff

LOG: [flang] Portability warning and documentation for an obscure extension

A quotation mark can appear in a Fortran character literal by doubling
it; for example, PRINT *, "'""'" prints '"'.  When those doubled
quotation marks are split by a free form line continuation, the
continuation line should have an ampersand before the second quotation
mark.  But most compilers, including this one, allow the second
quotation mark to appear as the first character on the continuation
line, too.

So this works:

  print *, "'"&
"'"

but it really should be written as:

  print *, "'"&
&"'"

Emit a portability warning and document that we support this near-universal
extension.

Differential Revision: https://reviews.llvm.org/D155973

Added: 
    flang/test/Parser/continuation-before-quote.f90

Modified: 
    flang/docs/Extensions.md
    flang/lib/Parser/prescan.cpp

Removed: 
    


################################################################################
diff  --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index 5938ecc17c6c38..4646e0ba501b9f 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -291,6 +291,10 @@ end
   numeric character literal kind prefix on the file name.
 * Intrinsic procedures TAND and ATAND. Constant folding is currently
   not supported for these procedures but this is planned.
+* When a pair of quotation marks in a character literal are split
+  by a line continuation in free form, the second quotation mark
+  may appear at the beginning of the continuation line without an
+  ampersand, althought one is required by the standard.
 
 ### Extensions supported when enabled by options
 
@@ -607,3 +611,4 @@ end module
 * `ENCODING=` is not in the list of changeable modes on an I/O unit,
   but every Fortran compiler allows the encoding to be changed on an
   open unit.
+

diff  --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 09b31b1dc7cc97..d84b62cbc30fb9 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -726,6 +726,11 @@ void Prescanner::QuotedCharacterLiteral(
         break;
       }
       inCharLiteral_ = true;
+      if (insertASpace_) {
+        Say(GetProvenanceRange(at_, end),
+            "Repeated quote mark in character literal continuation line should have been preceded by '&'"_port_en_US);
+        insertASpace_ = false;
+      }
     }
   }
   inCharLiteral_ = false;

diff  --git a/flang/test/Parser/continuation-before-quote.f90 b/flang/test/Parser/continuation-before-quote.f90
new file mode 100644
index 00000000000000..4ae669f5ac2769
--- /dev/null
+++ b/flang/test/Parser/continuation-before-quote.f90
@@ -0,0 +1,10 @@
+! RUN: %flang_fc1 -fsyntax-only %s 2>&1 | FileCheck %s
+! Continuation between repeated quotation marks
+subroutine test
+!CHECK: portability: Repeated quote mark in character literal continuation line should have been preceded by '&'
+  print *, 'needs an '&
+'ampersand'''
+!CHECK-NOT: portability: Repeated quote mark in character literal continuation line should have been preceded by '&'
+  print *, 'has an '&
+&'ampersand'''
+end