Add documentation to the flake8-gettext (INT) rules (#5813)

## Summary

Completes documentation for the `flake8-gettext` (`INT`) ruleset.
Related to #2646.

## Test Plan

`python scripts/check_docs_formatted.py`

crates/ruff/src/checkers/ast/mod.rs

@@ -2900,7 +2900,7 @@ where
                     Rule::FStringInGetTextFuncCall,
                     Rule::FormatInGetTextFuncCall,
                     Rule::PrintfInGetTextFuncCall,
-                ]) && flake8_gettext::rules::is_gettext_func_call(
+                ]) && flake8_gettext::is_gettext_func_call(
                     func,
                     &self.settings.flake8_gettext.functions_names,
                 ) {

crates/ruff/src/rules/flake8_gettext/mod.rs

@@ -1,7 +1,18 @@
 //! Rules from [flake8-gettext](https://pypi.org/project/flake8-gettext/).
+use rustpython_parser::ast::{self, Expr};
+
 pub(crate) mod rules;
 pub mod settings;
 
+/// Returns true if the [`Expr`] is an internationalization function call.
+pub(crate) fn is_gettext_func_call(func: &Expr, functions_names: &[String]) -> bool {
+    if let Expr::Name(ast::ExprName { id, .. }) = func {
+        functions_names.contains(id)
+    } else {
+        false
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::path::Path;

crates/ruff/src/rules/flake8_gettext/rules/f_string_in_gettext_func_call.rs

@@ -5,6 +5,40 @@ use ruff_macros::{derive_message_formats, violation};
 
 use crate::checkers::ast::Checker;
 
+/// ## What it does
+/// Checks for f-strings in `gettext` function calls.
+///
+/// ## Why is this bad?
+/// In the `gettext` API, the `gettext` function (often aliased to `_`) returns
+/// a translation of its input argument by looking it up in a translation
+/// catalog.
+///
+/// Calling `gettext` with an f-string as its argument can cause unexpected
+/// behavior. Since the f-string is resolved before the function call, the
+/// translation catalog will look up the formatted string, rather than the
+/// f-string template.
+///
+/// Instead, format the value returned by the function call, rather than
+/// its argument.
+///
+/// ## Example
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _(f"Hello, {name}!")  # Looks for "Hello, Maria!".
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _("Hello, %s!") % name  # Looks for "Hello, %s!".
+/// ```
+///
+/// ## References
+/// - [Python documentation: gettext](https://docs.python.org/3/library/gettext.html)
 #[violation]
 pub struct FStringInGetTextFuncCall;
 

crates/ruff/src/rules/flake8_gettext/rules/format_in_gettext_func_call.rs

@@ -5,6 +5,40 @@ use ruff_macros::{derive_message_formats, violation};
 
 use crate::checkers::ast::Checker;
 
+/// ## What it does
+/// Checks for `str.format` calls in `gettext` function calls.
+///
+/// ## Why is this bad?
+/// In the `gettext` API, the `gettext` function (often aliased to `_`) returns
+/// a translation of its input argument by looking it up in a translation
+/// catalog.
+///
+/// Calling `gettext` with a formatted string as its argument can cause
+/// unexpected behavior. Since the formatted string is resolved before the
+/// function call, the translation catalog will look up the formatted string,
+/// rather than the `str.format`-style template.
+///
+/// Instead, format the value returned by the function call, rather than
+/// its argument.
+///
+/// ## Example
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _("Hello, %s!" % name)  # Looks for "Hello, Maria!".
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _("Hello, %s!") % name  # Looks for "Hello, %s!".
+/// ```
+///
+/// ## References
+/// - [Python documentation: gettext](https://docs.python.org/3/library/gettext.html)
 #[violation]
 pub struct FormatInGetTextFuncCall;
 

crates/ruff/src/rules/flake8_gettext/rules/mod.rs

@@ -1,9 +1,7 @@
 pub(crate) use f_string_in_gettext_func_call::*;
 pub(crate) use format_in_gettext_func_call::*;
-pub(crate) use is_gettext_func_call::*;
 pub(crate) use printf_in_gettext_func_call::*;
 
 mod f_string_in_gettext_func_call;
 mod format_in_gettext_func_call;
-mod is_gettext_func_call;
 mod printf_in_gettext_func_call;

crates/ruff/src/rules/flake8_gettext/rules/printf_in_gettext_func_call.rs

@@ -4,6 +4,40 @@ use crate::checkers::ast::Checker;
 use ruff_diagnostics::{Diagnostic, Violation};
 use ruff_macros::{derive_message_formats, violation};
 
+/// ## What it does
+/// Checks for printf-style formatted strings in `gettext` function calls.
+///
+/// ## Why is this bad?
+/// In the `gettext` API, the `gettext` function (often aliased to `_`) returns
+/// a translation of its input argument by looking it up in a translation
+/// catalog.
+///
+/// Calling `gettext` with a formatted string as its argument can cause
+/// unexpected behavior. Since the formatted string is resolved before the
+/// function call, the translation catalog will look up the formatted string,
+/// rather than the printf-style template.
+///
+/// Instead, format the value returned by the function call, rather than
+/// its argument.
+///
+/// ## Example
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _("Hello, {}!".format(name))  # Looks for "Hello, Maria!".
+/// ```
+///
+/// Use instead:
+/// ```python
+/// from gettext import gettext as _
+///
+/// name = "Maria"
+/// _("Hello, %s!") % name  # Looks for "Hello, %s!".
+/// ```
+///
+/// ## References
+/// - [Python documentation: gettext](https://docs.python.org/3/library/gettext.html)
 #[violation]
 pub struct PrintfInGetTextFuncCall;