Reintroduce the lint targets in the linter script

changelog.d/12455.misc

@@ -0,0 +1 @@
+Reintroduce the list of targets to the linter script, to avoid linting unwanted local-only directories during development.

docs/code_style.md

@@ -6,60 +6,36 @@ The Synapse codebase uses a number of code formatting tools in order to
 quickly and automatically check for formatting (and sometimes logical)
 errors in code.
 
-The necessary tools are detailed below.
+The necessary tools are:
 
-First install them with:
+- [black](https://black.readthedocs.io/en/stable/), a source code formatter;
+- [isort](https://pycqa.github.io/isort/), which organises each file's imports;
+- [flake8](https://flake8.pycqa.org/en/latest/), which can spot common errors; and
+- [mypy](https://mypy.readthedocs.io/en/stable/), a type checker.
+
+Install them with:
 
 ```sh
 pip install -e ".[lint,mypy]"
 ```
 
--   **black**
-
-    The Synapse codebase uses [black](https://pypi.org/project/black/)
-    as an opinionated code formatter, ensuring all comitted code is
-    properly formatted.
-
-    Have `black` auto-format your code (it shouldn't change any
-    functionality) with:
-
-    ```sh
-    black .
-    ```
-
--   **flake8**
-
-    `flake8` is a code checking tool. We require code to pass `flake8`
-    before being merged into the codebase.
-
-    Check all application and test code with:
+The easiest way to run the lints is to invoke the linter script as follows.
 
-    ```sh
-    flake8 .
-    ```
-
--   **isort**
-
-    `isort` ensures imports are nicely formatted, and can suggest and
-    auto-fix issues such as double-importing.
-
-    Auto-fix imports with:
-
-    ```sh
-    isort .
-    ```
+```sh
+scripts-dev/lint.sh
+```
 
 It's worth noting that modern IDEs and text editors can run these tools
 automatically on save. It may be worth looking into whether this
 functionality is supported in your editor for a more convenient
-development workflow. It is not, however, recommended to run `flake8` on
-save as it takes a while and is very resource intensive.
+development workflow. It is not, however, recommended to run `flake8` or `mypy`
+on save as they take a while and can be very resource intensive.
 
 ## General rules
 
 -   **Naming**:
-    -   Use camel case for class and type names
-    -   Use underscores for functions and variables.
+    -   Use `CamelCase` for class and type names
+    -   Use underscores for `function_names` and `variable_names`.
 -   **Docstrings**: should follow the [google code
     style](https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings).
     See the

scripts-dev/lint.sh

@@ -79,8 +79,20 @@ else
   # If we were not asked to lint changed files, and no paths were found as a result,
   # then lint everything!
   if [[ -z ${files+x} ]]; then
-    # Lint all source code files and directories
-      files=( "." )
+      # CI runs each linter on the entire checkout, e.g. `black .`. So don't
+      # rely on this list to *find* lint targets if that misses a file; instead;
+      # use it to exclude files from linters when this can't be done by config.
+      #
+      # To check which files the linters examine, use:
+      #     black --verbose . 2>&1 | \grep -v ignored
+      #     isort --show-files .
+      #     flake8 --verbose .  # This isn't a great option
+      #     mypy has explicit config in mypy.ini; there is also mypy --verbose
+      files=(
+          "synapse" "docker" "tests"
+          "scripts-dev"
+          "contrib" "setup.py" "synmark" "stubs" ".ci"
+      )
   fi
 fi