Re-arrange some docstring modules (#428)

src/docstrings/helpers.rs

@@ -0,0 +1,37 @@
+use rustpython_ast::{Expr, Location};
+
+use crate::ast::types::Range;
+use crate::check_ast::Checker;
+
+/// Extract the leading words from a line of text.
+pub fn leading_words(line: &str) -> String {
+    line.trim()
+        .chars()
+        .take_while(|char| char.is_alphanumeric() || char.is_whitespace())
+        .collect()
+}
+
+/// Extract the leading whitespace from a line of text.
+pub fn leading_space(line: &str) -> String {
+    line.chars()
+        .take_while(|char| char.is_whitespace())
+        .collect()
+}
+
+/// Extract the leading indentation from a docstring.
+pub fn indentation<'a>(checker: &'a mut Checker, docstring: &Expr) -> &'a str {
+    let range = range_for(docstring);
+    checker.locator.slice_source_code_range(&Range {
+        location: Location::new(range.location.row(), 1),
+        end_location: Location::new(range.location.row(), range.location.column()),
+    })
+}
+
+/// Extract the source code range for a docstring.
+pub fn range_for(docstring: &Expr) -> Range {
+    // RustPython currently omits the first quotation mark in a string, so offset the location.
+    Range {
+        location: Location::new(docstring.location.row(), docstring.location.column() - 1),
+        end_location: docstring.end_location,
+    }
+}