[flang-commits] [flang] [flang] Allow C style comments in continuation lines (PR #214336)
Leandro Lupori via flang-commits
flang-commits at lists.llvm.org
Tue Aug 18 10:57:46 PDT 2026
https://github.com/luporl updated https://github.com/llvm/llvm-project/pull/214336
>From c6ef42313f4006efb2621b79a118dd62001e17bd Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Wed, 5 Aug 2026 17:25:35 -0300
Subject: [PATCH 1/4] [flang] Allow C style comments in continuation lines and
directives
Fixes #129455
---
flang/lib/Parser/prescan.cpp | 6 +++
.../Parser/continuation-before-c-comment.f90 | 38 +++++++++++++++++++
2 files changed, 44 insertions(+)
create mode 100644 flang/test/Parser/continuation-before-c-comment.f90
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 262954d32f266..1e0afd82c5f31 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -664,6 +664,12 @@ const char *Prescanner::SkipWhiteSpaceIncludingEmptyMacros(
while (true) {
if (int n{IsSpaceOrTab(p)}) {
p += n;
+ } else if (IsCComment(p)) {
+ if (const char *after{SkipCComment(p)}) {
+ p = after;
+ } else {
+ break;
+ }
} else if (preprocessor_.AnyDefinitions() && IsLegalIdentifierStart(*p)) {
// Skip keyword macros with empty definitions
const char *q{p + 1};
diff --git a/flang/test/Parser/continuation-before-c-comment.f90 b/flang/test/Parser/continuation-before-c-comment.f90
new file mode 100644
index 0000000000000..0049a363350c0
--- /dev/null
+++ b/flang/test/Parser/continuation-before-c-comment.f90
@@ -0,0 +1,38 @@
+! RUN: %flang_fc1 -fopenmp -fdebug-unparse %s 2>&1 | FileCheck %s
+! Continuation before C style comment.
+
+integer :: i
+
+! CHECK: i=1
+/* comment 1 */
+i&
+/* comment 2 */
+=1
+
+! CHECK: i=2
+ /* comment 1 */
+ i&
+ /* comment 2 */
+ =2
+
+! CHECK: i=3
+ /* comment 1 */
+ i&
+ /* comment 2 */
+ =3
+
+! CHECK: i=4
+ /* comment 1 */
+ i& /* inline comment */
+ /* comment 2 */
+ =4
+
+! CHECK: !$OMP PARALLEL DO
+ /* comments before directives are allowed now */ !$omp parallel do
+ do i = 1, 10
+ end do
+
+! CHECK: PRINT *, "pass"
+ /* C comment */
+ print *,'pass'
+end
>From 83e2e50a8b3eb8ec93418bfb8f4f62b2719911d3 Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Thu, 13 Aug 2026 17:06:23 -0300
Subject: [PATCH 2/4] Fix support for multi-line C style comments
And drop support for comments before compiler directives, to reduce
the amount of changes needed.
---
flang/lib/Parser/prescan.cpp | 48 +++++++++++++------
flang/lib/Parser/prescan.h | 3 +-
.../Parser/continuation-before-c-comment.f90 | 41 ++++++++++++----
3 files changed, 67 insertions(+), 25 deletions(-)
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index 1e0afd82c5f31..e75a221f41889 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -625,11 +625,7 @@ void Prescanner::SkipCComments() {
while (true) {
if (IsCComment(at_)) {
if (const char *after{SkipCComment(at_)}) {
- column_ += after - at_;
- // May have skipped over one or more newlines; relocate the start of
- // the next line.
- nextLine_ = at_ = after;
- NextLine();
+ UpdateSourcePositionAfterSkip(after);
} else {
// Don't emit any messages about unclosed C-style comments, because
// the sequence /* can appear legally in a FORMAT statement. There's
@@ -660,11 +656,11 @@ const char *Prescanner::SkipWhiteSpace(const char *p) {
}
const char *Prescanner::SkipWhiteSpaceIncludingEmptyMacros(
- const char *p) const {
+ const char *p, bool skipCComments) const {
while (true) {
if (int n{IsSpaceOrTab(p)}) {
p += n;
- } else if (IsCComment(p)) {
+ } else if (skipCComments && IsCComment(p)) {
if (const char *after{SkipCComment(p)}) {
p = after;
} else {
@@ -719,6 +715,27 @@ const char *Prescanner::SkipCComment(const char *p) const {
return p;
}
+// When skipping over C-style comments, one or more newlines may be skipped.
+// Adjust current position, column, and next line in source.
+void Prescanner::UpdateSourcePositionAfterSkip(const char *after) {
+ if (at_ >= after) {
+ return;
+ }
+ const char *nl{after - 1};
+ while (nl > at_ && *nl != '\n') {
+ --nl;
+ }
+ if (*nl == '\n' && after >= nextLine_) {
+ tabInCurrentLine_ = false;
+ column_ = after - nl;
+ nextLine_ = nl + 1;
+ NextLine();
+ } else {
+ column_ += after - at_;
+ }
+ at_ = after;
+}
+
bool Prescanner::NextToken(TokenSequence &tokens) {
CHECK(at_ >= start_ && at_ < limit_);
if (InFixedFormSource() && !preprocessingOnly_) {
@@ -1340,6 +1357,7 @@ bool Prescanner::SkipCommentLine(bool afterAmpersand) {
} else {
auto lineClass{ClassifyLine(nextLine_)};
if (lineClass.kind == LineClassification::Kind::Comment) {
+ nextLine_ += lineClass.payloadOffset; // advance to '!' or newline
NextLine();
return true;
} else if (lineClass.kind ==
@@ -1470,7 +1488,7 @@ const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
if (p >= limit_) {
return nullptr;
}
- p = SkipWhiteSpaceIncludingEmptyMacros(p);
+ p = SkipWhiteSpaceIncludingEmptyMacros(p, /*skipCComments=*/true);
if (InCompilerDirective()) {
if (InConditionalLine()) {
if (preprocessingOnly_) {
@@ -1594,8 +1612,8 @@ bool Prescanner::FreeFormContinuation() {
}
do {
if (const char *cont{FreeFormContinuationLine(ampersand)}) {
- BeginSourceLine(cont);
- NextLine();
+ UpdateSourcePositionAfterSkip(cont);
+ tabInCurrentLine_ = false;
return true;
}
} while (SkipCommentLine(ampersand));
@@ -1701,7 +1719,8 @@ Prescanner::IsFixedFormCompilerDirectiveLine(const char *start) const {
std::optional<Prescanner::LineClassification>
Prescanner::IsFreeFormCompilerDirectiveLine(const char *start) const {
- if (const char *p{SkipWhiteSpaceIncludingEmptyMacros(start)};
+ if (const char *p{
+ SkipWhiteSpaceIncludingEmptyMacros(start, /*skipCComments=*/false)};
p && *p == '!') {
if (auto lnClass{IsCompilerDirectiveSentinelAfterKeywordMacro(p + 1)}) {
if (lnClass->kind == LineClassification::Kind::CompilerDirective) {
@@ -1934,7 +1953,7 @@ bool Prescanner::CompilerDirectiveContinuation(
if (nextContinuation) {
// What follows is !DIR$ & xxx; skip over the & so that it
// doesn't cause a spurious continuation.
- at_ = nextContinuation;
+ UpdateSourcePositionAfterSkip(nextContinuation);
} else {
// What follows looks like a source line before macro expansion,
// but might become a directive continuation afterwards.
@@ -1990,10 +2009,9 @@ bool Prescanner::SourceLineContinuation(TokenSequence &tokens) {
NextLine();
return true;
} else if (const char *nextContinuation{FreeFormContinuationLine(true)}) {
- BeginSourceLine(nextLine_);
- NextLine();
+ UpdateSourcePositionAfterSkip(nextContinuation);
+ tabInCurrentLine_ = false;
TokenSequence followingTokens;
- at_ = nextContinuation;
while (NextToken(followingTokens)) {
}
if (auto followingPrepro{
diff --git a/flang/lib/Parser/prescan.h b/flang/lib/Parser/prescan.h
index 8f4f390d4ea37..30ff8bf7c7811 100644
--- a/flang/lib/Parser/prescan.h
+++ b/flang/lib/Parser/prescan.h
@@ -223,9 +223,10 @@ class Prescanner {
void SkipCComments();
void SkipSpaces();
static const char *SkipWhiteSpace(const char *);
- const char *SkipWhiteSpaceIncludingEmptyMacros(const char *) const;
+ const char *SkipWhiteSpaceIncludingEmptyMacros(const char *, bool) const;
const char *SkipWhiteSpaceAndCComments(const char *) const;
const char *SkipCComment(const char *) const;
+ void UpdateSourcePositionAfterSkip(const char *);
bool NextToken(TokenSequence &);
bool HandleExponent(TokenSequence &);
bool HandleKindSuffix(TokenSequence &);
diff --git a/flang/test/Parser/continuation-before-c-comment.f90 b/flang/test/Parser/continuation-before-c-comment.f90
index 0049a363350c0..33b2291c4d280 100644
--- a/flang/test/Parser/continuation-before-c-comment.f90
+++ b/flang/test/Parser/continuation-before-c-comment.f90
@@ -3,36 +3,59 @@
integer :: i
+! Single line comment.
! CHECK: i=1
/* comment 1 */
i&
/* comment 2 */
=1
-
! CHECK: i=2
/* comment 1 */
i&
/* comment 2 */
=2
-
! CHECK: i=3
/* comment 1 */
i&
/* comment 2 */
=3
-
! CHECK: i=4
/* comment 1 */
i& /* inline comment */
/* comment 2 */
=4
-! CHECK: !$OMP PARALLEL DO
- /* comments before directives are allowed now */ !$omp parallel do
- do i = 1, 10
- end do
+! Multi-line comment.
+! CHECK: i=5
+i&
+/* c
+*/ = 5
+
+! Compiler directive.
+! CHECK: !$OMP PARALLEL
+! CHECK: !$OMP END PARALLEL
+!$omp para&
+/* comment */
+!$omp llel
+!$omp end parallel
+! CHECK: !$OMP PARALLEL
+! CHECK: !$OMP END PARALLEL
+!$omp para&
+/* multi
+ * line */
+!$omp llel
+!$omp end parallel
+! Source line continuation after macro expansion.
+! CHECK: i=12
+! CHECK: i=14
! CHECK: PRINT *, "pass"
- /* C comment */
- print *,'pass'
+#define CONT &
+i = 6 CONT
+/* comment */
++ 6
+i = 7 CONT
+/* multi
+ * line */ + 7
+print *,'pass'
end
>From f2f099ae03d0b8991e305dfdd05e316577008642 Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Thu, 13 Aug 2026 18:47:22 -0300
Subject: [PATCH 3/4] Don't clear tabInCurrentLine_ in
UpdateSourcePositionAfterSkip
---
flang/lib/Parser/prescan.cpp | 1 -
1 file changed, 1 deletion(-)
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index e75a221f41889..edbce401d74fc 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -726,7 +726,6 @@ void Prescanner::UpdateSourcePositionAfterSkip(const char *after) {
--nl;
}
if (*nl == '\n' && after >= nextLine_) {
- tabInCurrentLine_ = false;
column_ = after - nl;
nextLine_ = nl + 1;
NextLine();
>From 8af242b7fd7d67c02a8dfe62b38be1198f040857 Mon Sep 17 00:00:00 2001
From: Leandro Lupori <leandro.lupori at linaro.org>
Date: Mon, 17 Aug 2026 16:15:17 -0300
Subject: [PATCH 4/4] Warn when C-style comments are used in continuation lines
---
flang/lib/Parser/prescan.cpp | 48 ++++++++++++++-----
flang/lib/Parser/prescan.h | 5 +-
...90 => continuation-before-c-comment01.f90} | 0
.../continuation-before-c-comment02.f90 | 15 ++++++
4 files changed, 54 insertions(+), 14 deletions(-)
rename flang/test/Parser/{continuation-before-c-comment.f90 => continuation-before-c-comment01.f90} (100%)
create mode 100644 flang/test/Parser/continuation-before-c-comment02.f90
diff --git a/flang/lib/Parser/prescan.cpp b/flang/lib/Parser/prescan.cpp
index edbce401d74fc..1cdc42f463457 100644
--- a/flang/lib/Parser/prescan.cpp
+++ b/flang/lib/Parser/prescan.cpp
@@ -641,6 +641,13 @@ void Prescanner::SkipCComments() {
}
}
+void Prescanner::WarnCComment(const char *at) {
+ if (features_.ShouldWarn(LanguageFeature::ClassicCComments)) {
+ Say(LanguageFeature::ClassicCComments, GetProvenance(at),
+ "nonstandard usage: C-style comment"_port_en_US);
+ }
+}
+
void Prescanner::SkipSpaces() {
while (IsSpaceOrTab(at_)) {
NextChar();
@@ -656,12 +663,16 @@ const char *Prescanner::SkipWhiteSpace(const char *p) {
}
const char *Prescanner::SkipWhiteSpaceIncludingEmptyMacros(
- const char *p, bool skipCComments) const {
+ const char *p, const char **cComment) const {
+ const char *firstCComment{nullptr};
while (true) {
if (int n{IsSpaceOrTab(p)}) {
p += n;
- } else if (skipCComments && IsCComment(p)) {
+ } else if (cComment && IsCComment(p)) {
if (const char *after{SkipCComment(p)}) {
+ if (!firstCComment) {
+ firstCComment = p;
+ }
p = after;
} else {
break;
@@ -682,6 +693,9 @@ const char *Prescanner::SkipWhiteSpaceIncludingEmptyMacros(
break;
}
}
+ if (cComment) {
+ *cComment = firstCComment;
+ }
return p;
}
@@ -743,10 +757,7 @@ bool Prescanner::NextToken(TokenSequence &tokens) {
if (*at_ == '/' && IsCComment(at_)) {
// Recognize and skip over classic C style /*comments*/ when
// outside a character literal.
- if (features_.ShouldWarn(LanguageFeature::ClassicCComments)) {
- Say(LanguageFeature::ClassicCComments, GetCurrentProvenance(),
- "nonstandard usage: C-style comment"_port_en_US);
- }
+ WarnCComment(at_);
SkipCComments();
}
if (IsSpaceOrTab(at_)) {
@@ -1481,13 +1492,9 @@ constexpr bool IsDirective(const char *match, const char *dir) {
return true;
}
-const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
+const char *Prescanner::GetFreeFormContinuationLine(
+ bool ampersand, const char *p) {
const char *lineStart{nextLine_};
- const char *p{lineStart};
- if (p >= limit_) {
- return nullptr;
- }
- p = SkipWhiteSpaceIncludingEmptyMacros(p, /*skipCComments=*/true);
if (InCompilerDirective()) {
if (InConditionalLine()) {
if (preprocessingOnly_) {
@@ -1573,6 +1580,21 @@ const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
}
}
+const char *Prescanner::FreeFormContinuationLine(bool ampersand) {
+ const char *lineStart{nextLine_};
+ const char *p{lineStart};
+ if (p >= limit_) {
+ return nullptr;
+ }
+ const char *cComment;
+ p = SkipWhiteSpaceIncludingEmptyMacros(lineStart, &cComment);
+ p = GetFreeFormContinuationLine(ampersand, p);
+ if (p && cComment) {
+ WarnCComment(cComment);
+ }
+ return p;
+}
+
bool Prescanner::FixedFormContinuation(bool atNewline) {
// N.B. We accept '&' as a continuation indicator in fixed form, too,
// but not in a character literal.
@@ -1719,7 +1741,7 @@ Prescanner::IsFixedFormCompilerDirectiveLine(const char *start) const {
std::optional<Prescanner::LineClassification>
Prescanner::IsFreeFormCompilerDirectiveLine(const char *start) const {
if (const char *p{
- SkipWhiteSpaceIncludingEmptyMacros(start, /*skipCComments=*/false)};
+ SkipWhiteSpaceIncludingEmptyMacros(start, /*cComment=*/nullptr)};
p && *p == '!') {
if (auto lnClass{IsCompilerDirectiveSentinelAfterKeywordMacro(p + 1)}) {
if (lnClass->kind == LineClassification::Kind::CompilerDirective) {
diff --git a/flang/lib/Parser/prescan.h b/flang/lib/Parser/prescan.h
index 30ff8bf7c7811..516f8962705b9 100644
--- a/flang/lib/Parser/prescan.h
+++ b/flang/lib/Parser/prescan.h
@@ -221,9 +221,11 @@ class Prescanner {
// True when input flowed to a continuation line
bool SkipToNextSignificantCharacter();
void SkipCComments();
+ void WarnCComment(const char *at);
void SkipSpaces();
static const char *SkipWhiteSpace(const char *);
- const char *SkipWhiteSpaceIncludingEmptyMacros(const char *, bool) const;
+ const char *SkipWhiteSpaceIncludingEmptyMacros(
+ const char *, const char **) const;
const char *SkipWhiteSpaceAndCComments(const char *) const;
const char *SkipCComment(const char *) const;
void UpdateSourcePositionAfterSkip(const char *);
@@ -241,6 +243,7 @@ class Prescanner {
void FortranInclude(const char *quote);
const char *IsPreprocessorDirectiveLine(const char *) const;
const char *FixedFormContinuationLine(bool atNewline);
+ const char *GetFreeFormContinuationLine(bool ampersand, const char *p);
const char *FreeFormContinuationLine(bool ampersand);
bool IsImplicitContinuation() const;
bool FixedFormContinuation(bool atNewline);
diff --git a/flang/test/Parser/continuation-before-c-comment.f90 b/flang/test/Parser/continuation-before-c-comment01.f90
similarity index 100%
rename from flang/test/Parser/continuation-before-c-comment.f90
rename to flang/test/Parser/continuation-before-c-comment01.f90
diff --git a/flang/test/Parser/continuation-before-c-comment02.f90 b/flang/test/Parser/continuation-before-c-comment02.f90
new file mode 100644
index 0000000000000..6f5e867ef6011
--- /dev/null
+++ b/flang/test/Parser/continuation-before-c-comment02.f90
@@ -0,0 +1,15 @@
+! RUN: not %flang_fc1 -fopenmp -pedantic -Werror -fdebug-unparse %s 2>&1 | FileCheck %s --check-prefix=ERROR
+! Continuation before C style comment.
+
+integer :: i
+i&
+! ERROR: portability: nonstandard usage: C-style comment
+/* c */ = &
+! ERROR: portability: nonstandard usage: C-style comment
+/* d */ 7
+if (i /= 7) then
+ print *, 'error', i
+else
+ print *, 'pass'
+end if
+end
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