catalog: add Cpp struct inheritance example

HerringtonDarkholme · HerringtonDarkholme · commit b382cfe4d698 · 2025-02-16T21:05:51.000-05:00
fix ast-grep#675
diff --git a/website/catalog/cpp/find-struct-inheritance.md b/website/catalog/cpp/find-struct-inheritance.md
@@ -0,0 +1,49 @@
+## Find Struct Inheritance
+
+* [Playground Link](/playground.html#eyJtb2RlIjoiUGF0Y2giLCJsYW5nIjoiY3BwIiwicXVlcnkiOiJzdHJ1Y3QgJFNPTUVUSElORzogICRJTkhFUklUU19GUk9NIHsgJCQkQk9EWTsgfSIsInJld3JpdGUiOiIiLCJzdHJpY3RuZXNzIjoic21hcnQiLCJzZWxlY3RvciI6IiIsImNvbmZpZyI6IiIsInNvdXJjZSI6InN0cnVjdCBGb286IEJhciB7fTtcblxuc3RydWN0IEJhcjogQmF6IHtcbiAgaW50IGEsIGI7XG59In0=)
+
+### Description
+
+ast-grep's pattern is AST based. A code snippet like `struct $SOMETHING:  $INHERITS` will not work because it does not have a correct AST structure. The correct pattern should spell out the full syntax like `struct $SOMETHING: $INHERITS { $$$BODY; }`.
+
+Compare the ast structure below to see the difference, especially the `ERROR` node. You can also use the playground's pattern panel to debug.
+
+:::code-group
+```shell [Wrong Pattern]
+ERROR
+  $SOMETHING
+  base_class_clause
+    $INHERITS
+```
+
+```shell [Correct Pattern]
+struct_specifier
+  $SOMETHING
+  base_class_clause
+    $INHERITS
+  field_declaration_list
+    field_declaration
+      $$$BODY
+```
+:::
+
+If it is not possible to write a full pattern, [YAML rule](/guide/rule-config.html) is a better choice.
+
+
+### Pattern
+```shell
+ast-grep --lang cpp --pattern '
+struct $SOMETHING: $INHERITS { $$$BODY; }'
+```
+
+### Example
+
+<!-- highlight matched code in curly-brace {lineNum} -->
+```cpp {1-3}
+struct Bar: Baz {
+  int a, b;
+}
+```
+
+### Contributed by
+Inspired by this [tweet](https://x.com/techno_bog/status/1885421768384331871)
diff --git a/website/catalog/cpp/index.md b/website/catalog/cpp/index.md
@@ -7,3 +7,4 @@ Cpp is a superset of C, so you can reuse Cpp rules with C code. The [`languageGl
 :::
 
 <!--@include: ./fix-format-vuln.md-->
+<!--@include: ./find-struct-inheritance.md-->

Original file line number	Diff line number	Diff line change
@@ -7,3 +7,4 @@ Cpp is a superset of C, so you can reuse Cpp rules with C code. The [`languageGl
`7`	`7`	`:::`
`8`	`8`
`9`	`9`	`<!--@include: ./fix-format-vuln.md-->`
	`10`	`+<!--@include: ./find-struct-inheritance.md-->`