[flang] Fix crash due to overly broad assertion

[klausler]

Fix #95689 and add a regression test.

[llvmbot]

@llvm/pr-subscribers-flang-parser

Author: Peter Klausler (klausler)

Changes

Fix #95689 and add a regression test.

---

Full diff: https://github.com/llvm/llvm-project/pull/95809.diff

2 Files Affected:

• (modified) flang/lib/Parser/prescan.cpp (+3-5)
• (added) flang/test/Preprocessing/multi-cont.F90 (+6)

diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 8efcd617cf0f9..2a6ecfbb0830e 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -185,11 +185,9 @@ void Prescanner::Statement() {
       // a comment marker or directive sentinel.  If so, disable line
       // continuation, so that NextToken() won't consume anything from
       // following lines.
-      if (IsLegalIdentifierStart(*at_)) {
-        CHECK(NextToken(tokens));
-        CHECK(tokens.SizeInTokens() == 1);
-        CharBlock id{tokens.TokenAt(0)};
-        if (preprocessor_.IsNameDefined(id) &&
+      if (IsLegalIdentifierStart(*at_) && NextToken(tokens) &&
+          tokens.SizeInTokens() > 0) {
+        if (CharBlock id{tokens.TokenAt(0)}; preprocessor_.IsNameDefined(id) &&
             !preprocessor_.IsFunctionLikeDefinition(id)) {
           if (auto replaced{preprocessor_.MacroReplacement(tokens, *this)}) {
             auto newLineClass{ClassifyLine(*replaced, GetCurrentProvenance())};
diff --git a/flang/test/Preprocessing/multi-cont.F90 b/flang/test/Preprocessing/multi-cont.F90
new file mode 100644
index 0000000000000..5a2c0b9c47976
--- /dev/null
+++ b/flang/test/Preprocessing/multi-cont.F90
@@ -0,0 +1,6 @@
+! RUN: %flang -E %s 2>&1 | FileCheck --strict-whitespace %s
+! CHECK:      print *, 666
+pr&
+&i&
+&nt *, 666
+end

[psteinfeld]

All builds and tests correctly and looks good.