From ab843b54560ae649ef179148ee9d747f866d4f9e Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Fri, 29 May 2026 14:23:10 +0100
Subject: [PATCH 1/8] Fix for issue 505 by removing blank line comments being
 generated as real Comments

---
 src/fparser/two/Fortran2003.py                |  6 +++
 .../two/tests/test_comments_and_directives.py | 42 +++++++++++++------
 2 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/src/fparser/two/Fortran2003.py b/src/fparser/two/Fortran2003.py
index 19ab1171..038c9f07 100644
--- a/src/fparser/two/Fortran2003.py
+++ b/src/fparser/two/Fortran2003.py
@@ -238,6 +238,12 @@ def __new__(cls, string, parent_cls=None):
         from fparser.common import readfortran
 
         if isinstance(string, readfortran.Comment):
+            # We can reach this with false readfortran.Comment nodes
+            # that represent empty lines in the original input. These
+            # have no syntactic relevance, and so are not kept by
+            # fparser.
+            if string.comment == "":
+                return
             # We were after a comment and we got a comment. Construct
             # one manually to avoid recursively calling this __new__
             # method again...
diff --git a/src/fparser/two/tests/test_comments_and_directives.py b/src/fparser/two/tests/test_comments_and_directives.py
index b7914dec..bedba960 100644
--- a/src/fparser/two/tests/test_comments_and_directives.py
+++ b/src/fparser/two/tests/test_comments_and_directives.py
@@ -35,7 +35,7 @@
 
 import pytest
 from fparser.two.Fortran2003 import Program, Comment, Directive, Subroutine_Subprogram
-from fparser.two.utils import walk
+from fparser.two.utils import walk, FortranSyntaxError
 from fparser.api import get_reader
 
 from fparser.two.parser import ParserFactory
@@ -92,7 +92,7 @@ def test_simple_prog():
         "  ! A full line comment\n"
         '  PRINT *, "Hello"\n'
         "  ! This block gets executed\n"
-        "END PROGRAM a_prog\n"
+        "END PROGRAM a_prog"
     )
 
 
@@ -120,7 +120,7 @@ def test_ifthen():
         '    PRINT *, "Hello"\n'
         "    ! Another full line comment\n"
         "  END IF\n"
-        "END PROGRAM a_prog\n"
+        "END PROGRAM a_prog"
     )
 
 
@@ -147,7 +147,7 @@ def test_inline_ifthen():
         "    ! An in-line comment here\n"
         "  END IF\n"
         "  ! A comment after a block\n"
-        "END PROGRAM a_prog\n"
+        "END PROGRAM a_prog"
     )
 
 
@@ -441,15 +441,11 @@ def test_directive_stmts():
     old = reader.get_item()
     assert old is not None
 
-    out = walk(program, Comment)
-    comments = 0
-    for comment in out:
-        if comment.items[0] != "":
-            comments = comments + 1
-    assert comments == 3
-    assert str(out[1]) == "!$dir inline"
-    assert str(out[3]) == "! A comment!"
-    assert str(out[4]) == "!!$ Another comment"
+    comments = walk(program, Comment)
+    assert len(comments) == 3
+    assert str(comments[0]) == "!$dir inline"
+    assert str(comments[1]) == "! A comment!"
+    assert str(comments[2]) == "!!$ Another comment"
 
     # Check that passing something that isn't a comment into a Directive
     # __new__ call doesn't create a Directive.
@@ -606,3 +602,23 @@ def test_inline_directive_is_comment():
     program = Program(reader)
     out = walk(program, Directive)
     assert len(out) == 0
+
+
+def test_syntax_error_with_comments():
+    """Test that when we keep comments we still correctly give syntax errors
+    when the first line of the file is a blank line."""
+    source = """
+module m
+  integer :: x
+contains
+  subroutine foo()
+    if (.true.)
+      x = 0
+    end if
+  end subroutine
+end module"""
+    reader = get_reader(source, ignore_comments=False)
+    with pytest.raises(FortranSyntaxError) as err:
+        program = Program(reader)
+    assert "at line 6\n" in str(err.value)
+    assert ">>>    if (.true.)\n" in str(err.value)

From a303e1d581f478026f56edb5d7a740af89390030 Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Fri, 29 May 2026 15:51:20 +0100
Subject: [PATCH 2/8] Fixes for reivew

---
 example/test_files/make_public_correct.f90            | 8 --------
 src/fparser/two/tests/test_comments_and_directives.py | 7 ++++++-
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/example/test_files/make_public_correct.f90 b/example/test_files/make_public_correct.f90
index 44af5932..617285fb 100644
--- a/example/test_files/make_public_correct.f90
+++ b/example/test_files/make_public_correct.f90
@@ -1,31 +1,23 @@
 MODULE a_mod
-
   ! Access_Stmt private will be removed:
-
   ! Attr_Spec with 0 and 1 additional attribute, the protected will be remobed
   REAL :: planet_radius = 123
   REAL, PARAMETER :: planet_radius_constant = 123
-
   LOGICAL :: public_protected = .FALSE.
   LOGICAL :: only_protected = .FALSE.
   LOGICAL :: private_protected = .FALSE.
-
   ! Access_stmt with public, this will be unmodified
   PUBLIC :: public_protected
   ! Protected_Stmt - the whole statement will be removed
   ! Access_stmt with private - the whole statement will be removed
-
   TYPE :: my_type
     ! Private_Components_Stmt in a type will be removed
     INTEGER :: a, b
     CONTAINS
     ! This private will also be removed.
-
   END TYPE my_type
-
   ! Access_Spec - the `private` will be removed
   TYPE(my_type), PUBLIC :: my_var
-
   CONTAINS
   SUBROUTINE sub_a
   END SUBROUTINE sub_a
diff --git a/src/fparser/two/tests/test_comments_and_directives.py b/src/fparser/two/tests/test_comments_and_directives.py
index bedba960..050fac4b 100644
--- a/src/fparser/two/tests/test_comments_and_directives.py
+++ b/src/fparser/two/tests/test_comments_and_directives.py
@@ -608,6 +608,11 @@ def test_syntax_error_with_comments():
     """Test that when we keep comments we still correctly give syntax errors
     when the first line of the file is a blank line."""
     source = """
+
+
+! This is module m
+
+
 module m
   integer :: x
 contains
@@ -620,5 +625,5 @@ def test_syntax_error_with_comments():
     reader = get_reader(source, ignore_comments=False)
     with pytest.raises(FortranSyntaxError) as err:
         program = Program(reader)
-    assert "at line 6\n" in str(err.value)
+    assert "at line 11\n" in str(err.value)
     assert ">>>    if (.true.)\n" in str(err.value)

From 3fde3acd09dd9b0260917ff5012fbafd9c41fc70 Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Mon, 1 Jun 2026 10:47:46 +0100
Subject: [PATCH 3/8] Add missing coverage

---
 .../two/tests/test_comments_and_directives.py | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/src/fparser/two/tests/test_comments_and_directives.py b/src/fparser/two/tests/test_comments_and_directives.py
index 050fac4b..d15b255c 100644
--- a/src/fparser/two/tests/test_comments_and_directives.py
+++ b/src/fparser/two/tests/test_comments_and_directives.py
@@ -627,3 +627,22 @@ def test_syntax_error_with_comments():
         program = Program(reader)
     assert "at line 11\n" in str(err.value)
     assert ">>>    if (.true.)\n" in str(err.value)
+
+
+def test_base_to_fortran_empty_comment():
+    """Test that if we have an empty comment we get the correct
+    to_fortran from the base class implementation (i.e. no tab)"""
+    source = """
+    !Comment
+    program test
+    end program
+    """
+    reader = get_reader(source, ignore_comments=False)
+    program = Program(reader)
+    out = walk(program, Comment)
+    comment = out[0]
+    assert comment.tofortran(tab="    ") == "    !Comment"
+    # Change the comment to be an empty comment.
+    comment.items = [""]
+    comment.item = ""
+    assert comment.tofortran(tab="    ") == ""

From e8d60b3a911e1e685ee2d820e40ed93da707dd98 Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Wed, 3 Jun 2026 13:51:30 +0100
Subject: [PATCH 4/8] Swap the fifo_item list to a deque

---
 src/fparser/common/readfortran.py | 15 ++++++++-------
 src/fparser/one/parsefortran.py   |  2 +-
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/src/fparser/common/readfortran.py b/src/fparser/common/readfortran.py
index bd536832..056feeff 100644
--- a/src/fparser/common/readfortran.py
+++ b/src/fparser/common/readfortran.py
@@ -141,6 +141,7 @@
 import re
 import sys
 import traceback
+from collections import deque
 from typing import Optional, Tuple
 from io import StringIO
 
@@ -594,7 +595,7 @@ def __init__(
         self.process_directives = process_directives
 
         self.filo_line = []  # used for un-consuming lines.
-        self.fifo_item = []
+        self.fifo_item = deque()
         self.source_lines = []  # source lines cache
 
         self.f2py_comment_lines = []  # line numbers of f2py directives
@@ -825,7 +826,7 @@ def put_item(self, item):
             # of the corresponding reader.
             self.reader.put_item(item)
         else:
-            self.fifo_item.insert(0, item)
+            self.fifo_item.appendleft(item)
 
     # Iterator methods:
 
@@ -930,11 +931,11 @@ def _next(self, ignore_comments=None):
         """
         if ignore_comments is None:
             ignore_comments = self._ignore_comments
-        fifo_item_pop = self.fifo_item.pop
+        fifo_item_pop = self.fifo_item.popleft
         while 1:
             try:
                 # first empty the FIFO item buffer:
-                item = fifo_item_pop(0)
+                item = fifo_item_pop()
             except IndexError:
                 # construct a new item from source
                 item = self.get_source_item()
@@ -986,8 +987,8 @@ def _next(self, ignore_comments=None):
                         items.append(new_line)
                 items.reverse()
                 for newitem in items:
-                    self.fifo_item.insert(0, newitem)
-                return fifo_item_pop(0)
+                    self.fifo_item.appendleft(newitem)
+                return fifo_item_pop()
         return item
 
     # Interface to returned items:
@@ -1663,7 +1664,7 @@ def get_source_item(self):
         # blank. If it is a comment, it has been pushed onto the
         # fifo_item list.
         try:
-            return self.fifo_item.pop(0)
+            return self.fifo_item.popleft()
         except IndexError:
             # A blank line is represented as an empty comment
             return Comment("", (startlineno, endlineno), self)
diff --git a/src/fparser/one/parsefortran.py b/src/fparser/one/parsefortran.py
index afb6b8c4..3ee86d2d 100644
--- a/src/fparser/one/parsefortran.py
+++ b/src/fparser/one/parsefortran.py
@@ -118,7 +118,7 @@ def put_item(self, item):
         """
         Pushes the given item to the reader.
         """
-        self.reader.fifo_item.insert(0, item)
+        self.reader.fifo_item.appendleft(item)
         return
 
     def parse(self):

From ec9ff56dbc8f8e46846b3969f0e8d496ce984ca9 Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Thu, 4 Jun 2026 14:07:15 +0100
Subject: [PATCH 5/8] Reintroduce empty lines, but fix the syntax bug in
 another way

---
 example/test_files/make_public_correct.f90       |  8 ++++++++
 src/fparser/two/Fortran2003.py                   | 10 +++-------
 .../two/tests/test_comments_and_directives.py    | 16 ++++++++--------
 3 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/example/test_files/make_public_correct.f90 b/example/test_files/make_public_correct.f90
index 617285fb..44af5932 100644
--- a/example/test_files/make_public_correct.f90
+++ b/example/test_files/make_public_correct.f90
@@ -1,23 +1,31 @@
 MODULE a_mod
+
   ! Access_Stmt private will be removed:
+
   ! Attr_Spec with 0 and 1 additional attribute, the protected will be remobed
   REAL :: planet_radius = 123
   REAL, PARAMETER :: planet_radius_constant = 123
+
   LOGICAL :: public_protected = .FALSE.
   LOGICAL :: only_protected = .FALSE.
   LOGICAL :: private_protected = .FALSE.
+
   ! Access_stmt with public, this will be unmodified
   PUBLIC :: public_protected
   ! Protected_Stmt - the whole statement will be removed
   ! Access_stmt with private - the whole statement will be removed
+
   TYPE :: my_type
     ! Private_Components_Stmt in a type will be removed
     INTEGER :: a, b
     CONTAINS
     ! This private will also be removed.
+
   END TYPE my_type
+
   ! Access_Spec - the `private` will be removed
   TYPE(my_type), PUBLIC :: my_var
+
   CONTAINS
   SUBROUTINE sub_a
   END SUBROUTINE sub_a
diff --git a/src/fparser/two/Fortran2003.py b/src/fparser/two/Fortran2003.py
index 038c9f07..1d3b2963 100644
--- a/src/fparser/two/Fortran2003.py
+++ b/src/fparser/two/Fortran2003.py
@@ -242,8 +242,8 @@ def __new__(cls, string, parent_cls=None):
             # that represent empty lines in the original input. These
             # have no syntactic relevance, and so are not kept by
             # fparser.
-            if string.comment == "":
-                return
+            #if string.comment == "":
+            #    return
             # We were after a comment and we got a comment. Construct
             # one manually to avoid recursively calling this __new__
             # method again...
@@ -426,11 +426,7 @@ def match(reader):
             # statement as this is optional in Fortran.
             #
             result = BlockBase.match(Main_Program0, [], None, reader)
-            if not result and comments:
-                # This program only contains comments.
-                return (content,)
-            else:
-                return result
+            return result
         except StopIteration:
             # Reader has no more lines.
             pass
diff --git a/src/fparser/two/tests/test_comments_and_directives.py b/src/fparser/two/tests/test_comments_and_directives.py
index d15b255c..ff0026b3 100644
--- a/src/fparser/two/tests/test_comments_and_directives.py
+++ b/src/fparser/two/tests/test_comments_and_directives.py
@@ -92,7 +92,7 @@ def test_simple_prog():
         "  ! A full line comment\n"
         '  PRINT *, "Hello"\n'
         "  ! This block gets executed\n"
-        "END PROGRAM a_prog"
+        "END PROGRAM a_prog\n"
     )
 
 
@@ -120,7 +120,7 @@ def test_ifthen():
         '    PRINT *, "Hello"\n'
         "    ! Another full line comment\n"
         "  END IF\n"
-        "END PROGRAM a_prog"
+        "END PROGRAM a_prog\n"
     )
 
 
@@ -147,7 +147,7 @@ def test_inline_ifthen():
         "    ! An in-line comment here\n"
         "  END IF\n"
         "  ! A comment after a block\n"
-        "END PROGRAM a_prog"
+        "END PROGRAM a_prog\n"
     )
 
 
@@ -442,10 +442,10 @@ def test_directive_stmts():
     assert old is not None
 
     comments = walk(program, Comment)
-    assert len(comments) == 3
-    assert str(comments[0]) == "!$dir inline"
-    assert str(comments[1]) == "! A comment!"
-    assert str(comments[2]) == "!!$ Another comment"
+    assert len(comments) == 5
+    assert str(comments[1]) == "!$dir inline"
+    assert str(comments[3]) == "! A comment!"
+    assert str(comments[4]) == "!!$ Another comment"
 
     # Check that passing something that isn't a comment into a Directive
     # __new__ call doesn't create a Directive.
@@ -640,7 +640,7 @@ def test_base_to_fortran_empty_comment():
     reader = get_reader(source, ignore_comments=False)
     program = Program(reader)
     out = walk(program, Comment)
-    comment = out[0]
+    comment = out[1]
     assert comment.tofortran(tab="    ") == "    !Comment"
     # Change the comment to be an empty comment.
     comment.items = [""]

From c402bdb3d309334cb300bab6462de20dea6a729a Mon Sep 17 00:00:00 2001
From: LonelyCat124 <3043914+LonelyCat124@users.noreply.github.com.>
Date: Thu, 4 Jun 2026 14:19:55 +0100
Subject: [PATCH 6/8] Remove old comments

---
 src/fparser/two/Fortran2003.py | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/src/fparser/two/Fortran2003.py b/src/fparser/two/Fortran2003.py
index 1d3b2963..177b40e4 100644
--- a/src/fparser/two/Fortran2003.py
+++ b/src/fparser/two/Fortran2003.py
@@ -238,12 +238,6 @@ def __new__(cls, string, parent_cls=None):
         from fparser.common import readfortran
 
         if isinstance(string, readfortran.Comment):
-            # We can reach this with false readfortran.Comment nodes
-            # that represent empty lines in the original input. These
-            # have no syntactic relevance, and so are not kept by
-            # fparser.
-            #if string.comment == "":
-            #    return
             # We were after a comment and we got a comment. Construct
             # one manually to avoid recursively calling this __new__
             # method again...
@@ -424,7 +418,6 @@ def match(reader):
             # Found a syntax error for this rule. Now look to match
             # (via Main_Program0) with a program containing no program
             # statement as this is optional in Fortran.
-            #
             result = BlockBase.match(Main_Program0, [], None, reader)
             return result
         except StopIteration:

From 73dd3a9989c1cd0a80c3365c0fef2f1bf9f17531 Mon Sep 17 00:00:00 2001
From: Sergi Siso <sergiesg@gmail.com>
Date: Thu, 4 Jun 2026 14:57:32 +0100
Subject: [PATCH 7/8] Update docstring and syntax

---
 src/fparser/common/readfortran.py                      | 5 ++---
 src/fparser/two/tests/fortran2003/test_program_r201.py | 8 +++-----
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/src/fparser/common/readfortran.py b/src/fparser/common/readfortran.py
index 056feeff..f8197a77 100644
--- a/src/fparser/common/readfortran.py
+++ b/src/fparser/common/readfortran.py
@@ -931,11 +931,10 @@ def _next(self, ignore_comments=None):
         """
         if ignore_comments is None:
             ignore_comments = self._ignore_comments
-        fifo_item_pop = self.fifo_item.popleft
         while 1:
             try:
                 # first empty the FIFO item buffer:
-                item = fifo_item_pop()
+                item = self.fifo_item.popleft()
             except IndexError:
                 # construct a new item from source
                 item = self.get_source_item()
@@ -988,7 +987,7 @@ def _next(self, ignore_comments=None):
                 items.reverse()
                 for newitem in items:
                     self.fifo_item.appendleft(newitem)
-                return fifo_item_pop()
+                return self.fifo_item.popleft()
         return item
 
     # Interface to returned items:
diff --git a/src/fparser/two/tests/fortran2003/test_program_r201.py b/src/fparser/two/tests/fortran2003/test_program_r201.py
index beac0079..7886bef3 100644
--- a/src/fparser/two/tests/fortran2003/test_program_r201.py
+++ b/src/fparser/two/tests/fortran2003/test_program_r201.py
@@ -42,14 +42,12 @@
 from fparser.api import get_reader
 from fparser.two.Fortran2003 import Program
 
-# Test no content or just white space. This is not officially a
-# Fortran rule but fortran compilers tend to accept empty content so
-# we follow their lead.
-
 
 def test_empty_input(f2003_create):
     """Test that empty input or input only containing white space can be
-    parsed succesfully
+    parsed succesfully. This is not valid fortran but it is accepted by
+    compilers and some applications produce it when there is files with
+    preprocessor ifdefs and includes but all resolve to emtpy strings.
 
     """
     for code in ["", "   ", "  \n  \n\n"]:

From a4fbd657809e3fb5863e4314a135ed5b92399335 Mon Sep 17 00:00:00 2001
From: Sergi Siso <sergiesg@gmail.com>
Date: Thu, 4 Jun 2026 15:20:43 +0100
Subject: [PATCH 8/8] Update changelog

---
 CHANGELOG.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b075f3c6..bd3b6f98 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,9 @@ Modifications by (in alphabetical order):
 * P. Vitt, University of Siegen, Germany
 * A. Voysey, UK Met Office
 
+04/06/2026 PR #509 for #505. Fix truncated syntax error reporting when files
+           have line breaks before the module or program. 
+
 21/04/2026 PR #502. Widen Proc_Decl (R1214) for Fortran 2008 to accept an
            initial-proc-target (R1217) on the right-hand side of ``=>``,
            not only null-init. See J3/10-007r1 §12.4.3.6.