Ignore preprocessor lines when detecting fixed form fortran

Currently a file with the content

```
#if defined(A) && !defined(B)
c This is a fixed-form style comment
#endif
```

is categorized as free-form Fortran because the preprocess if-clause contains ampersands and exclamation marks.

This commit makes the detection algorithm ignore all lines starting with `#` if pre-processing is enabled for that file. Pre-processor lines are not valid Fortran code and should IMO not be taken into account when trying to determine the Fortran form.

Author: albertziegenhagel

fortls/helper_functions.py

@@ -38,7 +38,7 @@ def expand_name(line: str, char_pos: int) -> str:
     return ""
 
 
-def detect_fixed_format(file_lines: list[str]) -> bool:
+def detect_fixed_format(file_lines: list[str], preproc: bool = False) -> bool:
     """Detect fixed/free format by looking for characters in label columns
     and variable declarations before column 6. Treat intersection format
     files as free format.
@@ -47,6 +47,9 @@ def detect_fixed_format(file_lines: list[str]) -> bool:
     ----------
     file_lines : list[str]
         List of consecutive file lines
+    preproc : bool
+        If true, preprocessor directives (lines starting with '#') will be
+        ignored
 
     Returns
     -------
@@ -68,8 +71,15 @@ def detect_fixed_format(file_lines: list[str]) -> bool:
     Lines wih ampersands are not fixed format
     >>> detect_fixed_format(['trailing line & ! comment'])
     False
+
+    But preprocessor lines might be ignored
+    >>> detect_fixed_format(['#if defined(A) && !defined(B)'], preproc=True)
+    True
     """
     for line in file_lines:
+        # Ignore preprocessor lines
+        if preproc and line.startswith("#"):
+            continue
         if FRegex.FREE_FORMAT_TEST.match(line):
             return False
         tmp_match = FRegex.VAR.match(line)

fortls/parsers/internal/parser.py

@@ -902,7 +902,7 @@ def load_from_disk(self) -> tuple[str | None, bool | None]:
 
             self.hash = hash
             self.contents_split = contents.splitlines()
-            self.fixed = detect_fixed_format(self.contents_split)
+            self.fixed = detect_fixed_format(self.contents_split, self.preproc)
             self.contents_pp = self.contents_split
             self.nLines = len(self.contents_split)
             return None, True
@@ -1011,7 +1011,7 @@ def set_contents(self, contents_split: list, detect_format: bool = True):
         self.contents_pp = self.contents_split
         self.nLines = len(self.contents_split)
         if detect_format:
-            self.fixed = detect_fixed_format(self.contents_split)
+            self.fixed = detect_fixed_format(self.contents_split, self.preproc)
 
     def get_line(self, line_no: int, pp_content: bool = False) -> str:
         """Get single line from file"""

test/test_helper.py

@@ -0,0 +1,20 @@
+from fortls.helper_functions import detect_fixed_format
+
+
+def test_detect_fixed_format():
+    assert detect_fixed_format([" free format"]) is False
+    assert detect_fixed_format([" INTEGER, PARAMETER :: N = 10"]) is False
+    assert detect_fixed_format(["C Fixed format"]) is True
+    assert detect_fixed_format(["trailing line & ! comment"]) is False
+    assert (
+        detect_fixed_format(
+            ["#if defined(A) && !defined(B)", "C Fixed format", "#endif"], preproc=True
+        )
+        is True
+    )
+    assert (
+        detect_fixed_format(
+            ["#if defined(A) && !defined(B)", " free format", "#endif"], preproc=True
+        )
+        is False
+    )