Fix indentation of structured multi-line comments

Closes #75

src/commonmark.rs

@@ -41,36 +41,66 @@ pub enum Argument {
 
 impl Argument {
     /// Write CommonMark structure for a single function argument.
+    /// We use the definition list extension, which prepends each argument with `: `.
+    /// For pattern arguments, we create a nested definition list.
     fn format_argument(self) -> String {
         match self {
-            // Write a flat argument entry.
+            // Write a flat argument entry, e.g. `id = x: x`
+            //
+            // `x`
+            // : Function argument
             Argument::Flat(arg) => {
                 format!(
                     "`{}`\n\n: {}\n\n",
                     arg.name,
-                    arg.doc.unwrap_or("Function argument".into()).trim()
+                    handle_indentation(arg.doc.unwrap_or("Function argument".into()).trim())
                 )
             }
 
             // Write a pattern argument entry and its individual
-            // parameters as a nested structure.
+            // parameters as a nested structure, e.g.:
+            //
+            // `foo = { a }: a`
+            //
+            // structured function argument
+            // : `a`
+            //   : Function argument
             Argument::Pattern(pattern_args) => {
                 let mut inner = String::new();
                 for pattern_arg in pattern_args {
                     inner += &Argument::Flat(pattern_arg).format_argument();
                 }
 
                 let indented = textwrap::indent(&inner, "  ");
-                // drop leading indentation, the `: ` serves this function already
+
                 format!(
+                    // The `:` creates another definition list of which `indented` is the term.
                     "structured function argument\n\n: {}",
+                    // drop leading indentation on the first line, the `: ` serves this function
+                    // already.
                     indented.trim_start()
                 )
             }
         }
     }
 }
 
+/// Since the first line starts with `: `, indent every other line by 2 spaces, so
+/// that the text aligns, to result in:
+///
+/// : first line
+///   every other line
+fn handle_indentation(raw: &str) -> String {
+    let result: String = match raw.split_once('\n') {
+        Some((first, rest)) => {
+            format!("{}\n{}", first, textwrap::indent(rest, "  "))
+        }
+        None => raw.into(),
+    };
+
+    result
+}
+
 /// Represents a single manual section describing a library function.
 #[derive(Clone, Debug)]
 pub struct ManualEntry {

src/main.rs

@@ -100,7 +100,7 @@ impl DocItem {
 /// Retrieve documentation comments.
 fn retrieve_doc_comment(node: &SyntaxNode, allow_line_comments: bool) -> Option<String> {
     // if the current node has a doc comment it'll be immediately preceded by that comment,
-    // or there will be a whitespace token and *then* the comment tokens before it. we merge
+    // or there will be a whitespace token and *then* the comment tokens before it. We merge
     // multiple line comments into one large comment if they are on adjacent lines for
     // documentation simplicity.
     let mut token = node.first_token()?.prev_token()?;
@@ -173,27 +173,47 @@ fn retrieve_doc_item(node: &AttrpathValue) -> Option<DocItem> {
     })
 }
 
-/// Dedent everything but the first line, whose indentation gets fully removed all the time
+/// Ensure all lines in a multi-line doc-comments have the same indentation.
 ///
-/// A doc comment like this in Nix:
+/// Consider such a doc comment:
 ///
+/// ```nix
 /// {
 ///   /* foo is
 ///   the value:
 ///     10
 ///   */
 ///   foo = 10;
 /// }
+/// ```
 ///
-/// The parser turns this into "foo is\n  the value:\n    10\n" where the first
-/// line has no leading indentation, but the rest do
+/// The parser turns this into:
 ///
-/// To align all lines to the same indentation, while preserving the
-/// formatting, we dedent all but the first line, while stripping any potential
-/// indentation from the first line.
+/// ```
+/// foo is
+///   the value:
+///     10
+/// ```
+///
+///
+/// where the first line has no leading indentation, and all other lines have preserved their
+/// original indentation.
+///
+/// What we want instead is:
+///
+/// ```
+/// foo is
+/// the value:
+///   10
+/// ```
+///
+/// i.e. we want the whole thing to be dedented. To achieve this, we remove all leading whitespace
+/// from the first line, and remove all common whitespace from the rest of the string.
 fn handle_indentation(raw: &str) -> Option<String> {
     let result: String = match raw.split_once('\n') {
-        Some((first, rest)) => format!("{}\n{}", first.trim(), dedent(rest)),
+        Some((first, rest)) => {
+            format!("{}\n{}", first.trim_start(), dedent(rest))
+        }
         None => raw.into(),
     };
 
@@ -248,18 +268,25 @@ fn collect_lambda_args(mut lambda: Lambda) -> Vec<Argument> {
 
     loop {
         match lambda.param().unwrap() {
+            // a variable, e.g. `id = x: x`
             Param::IdentParam(id) => {
                 args.push(Argument::Flat(SingleArg {
                     name: id.to_string(),
-                    doc: retrieve_doc_comment(id.syntax(), true),
+                    doc: handle_indentation(
+                        &retrieve_doc_comment(id.syntax(), true).unwrap_or_default(),
+                    ),
                 }));
             }
+            // an attribute set, e.g. `foo = { a }: a`
             Param::Pattern(pat) => {
+                // collect doc-comments for each attribute in the set
                 let pattern_vec: Vec<_> = pat
                     .pat_entries()
                     .map(|entry| SingleArg {
                         name: entry.ident().unwrap().to_string(),
-                        doc: retrieve_doc_comment(entry.syntax(), true),
+                        doc: handle_indentation(
+                            &retrieve_doc_comment(entry.syntax(), true).unwrap_or_default(),
+                        ),
                     })
                     .collect();
 
@@ -297,6 +324,9 @@ fn collect_entry_information(entry: AttrpathValue) -> Option<DocItem> {
     }
 }
 
+// a binding is an assignment, which can take place in an attrset
+// - as attributes
+// - as inherits
 fn collect_bindings(
     node: &SyntaxNode,
     category: &str,
@@ -334,6 +364,8 @@ fn collect_bindings(
     vec![]
 }
 
+// Main entrypoint for collection
+// TODO: document
 fn collect_entries(root: rnix::Root, category: &str) -> Vec<ManualEntry> {
     // we will look into the top-level let and its body for function docs.
     // we only need a single level of scope for this.
@@ -471,3 +503,21 @@ fn test_line_comments() {
 
     insta::assert_snapshot!(output);
 }
+
+#[test]
+fn test_multi_line() {
+    let mut output = Vec::new();
+    let src = fs::read_to_string("test/multi-line.nix").unwrap();
+    let nix = rnix::Root::parse(&src).ok().expect("failed to parse input");
+    let category = "let";
+
+    for entry in collect_entries(nix, category) {
+        entry
+            .write_section(&Default::default(), &mut output)
+            .expect("Failed to write section")
+    }
+
+    let output = String::from_utf8(output).expect("not utf8");
+
+    insta::assert_snapshot!(output);
+}

src/snapshots/nixdoc__multi_line.snap

@@ -0,0 +1,18 @@
+---
+source: src/main.rs
+expression: output
+---
+## `lib.let.f` {#function-library-lib.let.f}
+
+Some description
+
+structured function argument
+
+: `x`
+
+  : First line
+
+    Second line
+
+
+

test/multi-line.nix

@@ -0,0 +1,12 @@
+{
+  /* Some description */
+  f =
+    {
+      /* First line
+
+      Second line
+      */
+      x
+    ,
+    }: x;
+}