Merge pull request #134 from stfc/empty_input

Support Empty input files

CHANGELOG.md

@@ -11,6 +11,9 @@ Modifications by (in alphabetical order):
 * A. R. Porter, Science & Technology Facilities Council, UK
 * P. Vitt, University of Siegen, Germany
 
+28/11/2018 PR #134 for issue #119. Bug fix for parsing files that contain
+           nothing or just white space.
+
 23/11/2018 PR #122 for issue #118. Bug fix for reporting invalid
            Fortran when parsing `use module_name, only:` in fparser2.
 

doc/fparser2.rst

@@ -136,6 +136,11 @@ found in the code. Nodes representing in-line comments will be added
 immediately following the node representing the code in which they
 were encountered.
 
+Note that empty input, or input that consists of purely white space
+and/or newlines, is not treated as invalid Fortran and an empty AST is
+returned. Whilst this is not strictly valid, most compilers have this
+behaviour so we follow their lead.
+
 If the code is invalid Fortran then a `FortranSyntaxError` exception
 will be raised which indicates the offending line of code and its line
 number. For example:

src/fparser/two/Fortran2003.py

@@ -208,8 +208,10 @@ def __new__(cls, string):
         '''
         try:
             return Base.__new__(cls, string)
-        except NoMatchError as error:
-            raise FortranSyntaxError(string, error)
+        except NoMatchError:
+            # At the moment there is no useful information provided by
+            # NoMatchError so we pass on an empty string.
+            raise FortranSyntaxError(string, "")
 
     @staticmethod
     def match(reader):

src/fparser/two/tests/fortran2003/test_program_r201.py

@@ -32,7 +32,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-'''Test Fortran 2003 rule R201 : This file tests the support for one
+'''Test Fortran 2003 rule R201 : This file tests the support for zero
 or more program-units.
 
 '''
@@ -42,6 +42,21 @@
 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
+
+    '''
+    for code in ["", "   ", "  \n  \n\n"]:
+        reader = get_reader(code)
+        ast = Program(reader)
+        assert str(ast) == ""
+
 # Test single program units
 
 

src/fparser/two/utils.py

@@ -80,7 +80,11 @@ class FparserException(Exception):
     '''Base class exception for fparser. This allows an external tool to
     capture all exceptions if required.
 
+    :param str info: a string giving contextual error information.
+
     '''
+    def __init__(self, info):
+        Exception.__init__(self, info)
 
 
 class NoMatchError(FparserException):
@@ -105,23 +109,27 @@ class FortranSyntaxError(FparserException):
 
     '''
     def __init__(self, reader, info):
-        location = "at unknown location"
+        output = "at unknown location"
         if isinstance(reader, FortranReaderBase):
-            location = "at line {0}\n>>>{1}".format(
+            output = "at line {0}\n>>>{1}\n".format(
                 reader.linecount,
                 reader.source_lines[reader.linecount-1])
-        Exception.__init__(self, "{0}\n{1}".format(location, info))
+        if info:
+            output += "{0}".format(info)
+        FparserException.__init__(self, output)
 
 
 class InternalError(FparserException):
     '''An exception indicating that an unexpected error has occured in the
     parser.
 
+    :param str info: a string giving contextual error information.
+
     '''
     def __init__(self, info):
         new_info = ("'{0}'. Please report this to the "
                     "authors.".format(info))
-        Exception.__init__(self, new_info)
+        FparserException.__init__(self, new_info)
 
 
 def show_result(func):
@@ -286,9 +294,26 @@ def __new__(cls, string, parent_cls=None):
             raise AssertionError(repr(result))
         # If we get to here then we've failed to match the current line
         if isinstance(string, FortranReaderBase):
+            content = False
+            for index in range(string.linecount):
+                # Check all lines up to this one for content. We
+                # should be able to only check the current line but
+                # but as the line number returned is not always
+                # correct (due to coding errors) we can not assume the
+                # line pointed to is the line where the error actually
+                # happened.
+                if string.source_lines[index].strip():
+                    content = True
+                    break
+            if not content:
+                # There are no lines in the input or all lines up to
+                # this one are empty or contain only white space. This
+                # is typically accepted by fortran compilers so we
+                # follow their lead and do not raise an exception.
+                return
+            line = string.source_lines[string.linecount-1]
             errmsg = "at line {0}\n>>>{1}\n".format(
-                string.linecount,
-                string.source_lines[string.linecount-1])
+                string.linecount, line)
         else:
             errmsg = "{0}: '{1}'".format(cls.__name__, string)
         raise NoMatchError(errmsg)