tabs: align expansion to multiples of 8

README.md

@@ -352,6 +352,27 @@ def test_zen(patterns, zen_patterns):
     assert full_pattern == zen
 ```
 
+## Handling tabs and whitespace
+
+When copying and pasting output from commands its easy to turn tabs from an
+original source into spaces and then accidentally not aligning things right.
+
+As its more typical to not insert tabs in your code pytest-patterns converts
+tabs to spaces (properly aligned to 8 character stops as terminals render them):
+
+```python
+def test_tabs_and_spaces(patterns):
+    data = """
+pre>\taligned text
+prefix>\tmore aligned text
+"""
+    tabs = patterns.tabs
+    tabs.in_order("""
+pre>    aligned text
+prefix> aligned text
+""")
+    assert tabs == data
+```
 
 # Development
 
@@ -378,8 +399,7 @@ $ hatch run test
 
     -> whitespace (pattern and tested content)
         -> strip whitespace at beginning and end
-        -> replace tabs with spaces
-        -> fold multiple spaces into single spaces
+        -> fold multiple spaces into single spaces (makes it harder to diagnose things)
 
 * [ ] proper release process with tagging, version updates, etc.
 

src/pytest_patterns/plugin.py

@@ -2,7 +2,7 @@
 
 import enum
 import re
-from typing import Any, Iterator
+from typing import Any, Iterator, List, Set, Tuple
 
 import pytest
 
@@ -45,13 +45,19 @@ def symbol(self) -> str:
 
 EMPTY_LINE_PATTERN = "<empty-line>"
 
+def tab_replace(line: str) -> str:
+    while (position := line.find("\t")) != -1:
+        fill = " " * (8 - (position % 8))
+        line = line.replace("\t", fill)
+    return line
+
 
 def match(pattern: str, line: str) -> bool | re.Match[str] | None:
     if pattern == EMPTY_LINE_PATTERN:
         if not line:
             return True
-    pattern = pattern.replace("\t", " " * 8)
-    line = line.replace("\t", " " * 8)
+
+    line = tab_replace(line)
     pattern = re.escape(pattern)
     pattern = pattern.replace(r"\.\.\.", ".*?")
     re_pattern = re.compile("^" + pattern + "$")

tests/test_basics.py

@@ -11,6 +11,20 @@
     "",
 ]
 
+def test_tab_replace() -> None:
+    from pytest_patterns.plugin import tab_replace
+
+    assert tab_replace("\t") == " " * 8
+    assert tab_replace("1\t9") == "1       9"
+    assert tab_replace("12\t9") == "12      9"
+    assert tab_replace("123\t9") == "123     9"
+    assert tab_replace("1234\t9") == "1234    9"
+    assert tab_replace("12345\t9") == "12345   9"
+    assert tab_replace("123456\t9") == "123456  9"
+    assert tab_replace("1234567\t9") == "1234567 9"
+    assert tab_replace("12345678\t9") == "12345678        9"
+    assert tab_replace("123456789\t0") == "123456789       0"
+
 
 def test_patternslib_multiple_accesses(patterns: PatternsLib) -> None:
     assert patterns.foo is patterns.foo