[README] Expand no_trailing_whitespace example
Expand the no_trailing_whitespace example to work with 'shac fmt'.
Change-Id: Ib029169cf5e01519e7bc7877d64e17d94f11c26f
Reviewed-on: https://fuchsia-review.googlesource.com/c/shac-project/shac/+/1051018
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>
Fuchsia-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Oliver Newman <olivernewman@google.com>
diff --git a/README.md b/README.md
index 7518f13..24766e7 100644
--- a/README.md
+++ b/README.md
@@ -259,6 +259,45 @@
- black (success in 540ms)
```
+With a couple minor changes we can configure `no_trailing_whitespace` to work
+with `shac fmt` too. We need to rename the function from
+`no_trailing_whitespace` to `_no_trailing_whitespace`, add a `replacements`
+argument to `ctx.emit.finding()`, and register the check as a formatter. The
+`replacements` argument only applies to the characters between `col` and
+`end_col`. Since we want to remove those characters, we replace them with an
+empty string.
+
+```python
+def _no_trailing_whitespace(ctx):
+ """Check that no source files contain lines with trailing whitespace."""
+ for f in ctx.scm.affected_files():
+ contents = str(ctx.io.read_file(f))
+ for i, line in enumerate(contents.splitlines()):
+ stripped = line.rstrip()
+ if stripped != line:
+ ctx.emit.finding(
+ level = "error",
+ filepath = f,
+ # Finding lines and columns are 1-indexed.
+ line = i + 1,
+ col = len(stripped) + 1,
+ # End column is exclusive.
+ end_col = len(line) + 1,
+ message = "Delete trailing whitespace.",
+ replacements = [""]
+ )
+
+no_trailing_whitespace = shac.check(_no_trailing_whitespace, formatter = True)
+shac.register_check(no_trailing_whitespace)
+```
+
+Now `no_trailing_whitespace` will run in `shac fmt`:
+
+```shell
+$ shac fmt
+- no_trailing_whitespace (all good!)
+```
+
## Road map
Planned features/changes, in descending order by priority:
