From 5648afd950141a582b4585be8a30b7b3f808e35a Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 10 May 2026 15:23:52 +0100
Subject: Parse doc comment for struct definitions

---
 examples/01-struct/src/point.hob                   |  2 ++
 .../zwobble/hobgoblin/compiler/parser/Parser.java  | 28 +++++++++++++++++++---
 .../parser/ParserStructDefinitionTests.java        | 20 ++++++++++++++++
 3 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/examples/01-struct/src/point.hob b/examples/01-struct/src/point.hob
index abe989d..1f392af 100644
--- a/examples/01-struct/src/point.hob
+++ b/examples/01-struct/src/point.hob
@@ -1,8 +1,10 @@
+/// A straight line from one point to another.
 struct Line {
     field start: Point;
     field end: Point;
 }
 
+/// A 2D point.
 struct Point {
     field x: Int32;
     field y: Int32;
diff --git a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
index 88b0c5c..49464b6 100644
--- a/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
+++ b/src/main/java/org/zwobble/hobgoblin/compiler/parser/Parser.java
@@ -49,8 +49,10 @@ public class Parser {
     static UntypedNamespaceStatementNode parseNamespaceStatement(
         TokenIterator tokens
     ) {
+        var docComment = parseDocComment(tokens);
+
         if (tokens.isNext(TokenType.KEYWORD_STRUCT)) {
-            return parseStructDefinition(tokens);
+            return parseStructDefinition(tokens, docComment);
         } else if (tokens.isNext(TokenType.KEYWORD_SUM)) {
             return parseSumDefinition(tokens);
         } else {
@@ -58,8 +60,28 @@ public class Parser {
         }
     }
 
+    private static String parseDocComment(TokenIterator tokens) {
+        var docComment = new StringBuilder();
+
+        while (tokens.isNext(TokenType.DOC_COMMENT)) {
+            var docCommentToken = tokens.next(TokenType.DOC_COMMENT);
+            var docCommentLine = docCommentToken.charSequence();
+
+            var firstCharIndex = 3;
+            while (docCommentLine.charAt(firstCharIndex) == ' ') {
+                firstCharIndex++;
+            }
+
+            var docCommentContents = docCommentLine.subSequence(firstCharIndex, docCommentLine.length());
+            docComment.append(docCommentContents);
+        }
+
+        return docComment.toString();
+    }
+
     private static UntypedStructDefinitionNode parseStructDefinition(
-        TokenIterator tokens
+        TokenIterator tokens,
+        String docComment
     ) {
         var start = tokens.startPosition();
 
@@ -81,7 +103,7 @@ public class Parser {
         return new UntypedStructDefinitionNode(
             name.charSequence().toString(),
             fields,
-            "",
+            docComment,
             source
         );
     }
diff --git a/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
index 9dae394..a0394ce 100644
--- a/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
+++ b/src/test/java/org/zwobble/hobgoblin/compiler/parser/ParserStructDefinitionTests.java
@@ -70,4 +70,24 @@ public class ParserStructDefinitionTests {
             ))
         ));
     }
+
+    @Test
+    public void structWithDocComment() {
+        var source = """
+            /// A 2D point.
+            ///
+            /// Positive y is up.
+            struct Point {
+            }""";
+
+        var node = parseString(
+            source,
+            Parser::parseNamespaceStatement
+        );
+
+        assertThat(node, instanceOf(
+            UntypedStructDefinitionNode.class,
+            has("docComment", UntypedStructDefinitionNode::docComment, equalTo("A 2D point.\n\nPositive y is up.\n"))
+        ));
+    }
 }
-- 
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