[flang] Handle more use cases reported for issues/78797

[klausler]

I implemented legacy "token pasting" via line continuation for

call prefix&
&MACRO&
&suffix(1)

in a recent patch; this patch addresses the related cases

call prefix&
&MACRO&
&(1)

and

call &
&MACRO&
&suffix(1)

Fixes the latest #79590.

[llvmbot]

@llvm/pr-subscribers-flang-parser

Author: Peter Klausler (klausler)

Changes

I implemented legacy "token pasting" via line continuation for

call prefix&
&MACRO&
&suffix(1)

in a recent patch; this patch addresses the related cases

call prefix&
&MACRO&
&(1)

and

call &
&MACRO&
&suffix(1)

Fixes the latest #79590.

---

Full diff: https://github.com/llvm/llvm-project/pull/79628.diff

2 Files Affected:

• (modified) flang/lib/Parser/prescan.cpp (+15-5)
• (modified) flang/test/Preprocessing/pp134.F90 (+13-2)

diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index f7f22177a7d0bfa..26c6dd5a7ffe9c7 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -630,9 +630,11 @@ bool Prescanner::NextToken(TokenSequence &tokens) {
     preventHollerith_ = false;
   } else if (IsLegalInIdentifier(*at_)) {
     int parts{1};
+    const char *afterLast{nullptr};
     do {
       EmitChar(tokens, *at_);
       ++at_, ++column_;
+      afterLast = at_;
       if (SkipToNextSignificantCharacter() && IsLegalIdentifierStart(*at_)) {
         tokens.CloseToken();
         ++parts;
@@ -640,12 +642,20 @@ bool Prescanner::NextToken(TokenSequence &tokens) {
     } while (IsLegalInIdentifier(*at_));
     if (parts >= 3) {
       // Subtlety: When an identifier is split across three or more continuation
-      // lines, its parts are kept as distinct pp-tokens so that macro
-      // operates on them independently.  This trick accommodates the historic
-      // practice of using line continuation for token pasting after
-      // replacement.
+      // lines (or two continuation lines, immediately preceded or followed
+      // by '&' free form continuation line markers, its parts are kept as
+      // distinct pp-tokens so that macro operates on them independently.
+      // This trick accommodates the historic practice of using line
+      // continuation for token pasting after replacement.
     } else if (parts == 2) {
-      tokens.ReopenLastToken();
+      if ((start > start_ && start[-1] == '&') ||
+          (afterLast < limit_ && *afterLast == '&')) {
+        // call &                call foo&
+        //   &MACRO&      OR       &MACRO&
+        //   &foo(...)             &(...)
+      } else {
+        tokens.ReopenLastToken();
+      }
     }
     if (InFixedFormSource()) {
       SkipSpaces();
diff --git a/flang/test/Preprocessing/pp134.F90 b/flang/test/Preprocessing/pp134.F90
index 01e7b010d426ece..1b13e6cb91d7550 100644
--- a/flang/test/Preprocessing/pp134.F90
+++ b/flang/test/Preprocessing/pp134.F90
@@ -1,9 +1,20 @@
 ! RUN: %flang -E %s 2>&1 | FileCheck %s
-! CHECK: print *, ADC
+! CHECK: print *, ADC, 1
+! CHECK: print *, AD, 1
+! CHECK: print *, DC, 1
+! CHECK: print *, AB
 #define B D
 implicit none
 real ADC
 print *, A&
   &B&
-  &C
+  &C, 1
+print *, A&
+  &B&
+  &, 1
+print *, &
+  &B&
+  &C, 1
+print *, A&
+  &B
 end

[clementval]

LGTM

[mjklemm]

This PR looks good to me.

[bcornille]

Is there anything holding up this PR?

[clementval]

Is there anything holding up this PR?

Peter is in PTO right now.