Function merge_class_blocks 

fn merge_class_blocks(
    blocks: &[ClassBlockEntry],
) -> Result<Vec<WrapperFragment>, String>

Merge the impl blocks of each Rust type into one class fragment (#1776).

Blocks are grouped by ClassBlockEntry::type_path and taken in source order. A type’s fragment is the defining block’s head, with the class_docs of every block (the defining block’s first) at its CLASS_DOCS_MARKER line and the class_doc_lines of every block at its CLASS_DOC_LINES_MARKER line, then each block’s members, then the defining block’s tail. A tag repeated exactly is written once, and a generated CLASS_DEFAULT_PREFIX line gives way to the same tag on another block. A # Generated from Rust impl header precedes each part whose block differs from the previous part’s, so the duplicate-definition scan of the written file (detect_duplicate_wrapper_defs) names the block a definition comes from.

Every problem is collected into one message:

• two Rust types claim one R class name: their class objects and methods would overwrite each other when the package loads (#1677);
• the blocks of a type disagree on the class settings (ClassBlockEntry::settings), which shape every block’s members;
• two blocks of a type each have something only the defining block may have (ClassBlockEntry::defines);
• the doc comments of a type’s blocks give the class two titles, or a page other than the defining block’s (class_doc_conflicts);
• two blocks of a type bind the same member name (ClassBlockEntry::member_names), the later replacing the earlier;
• a type without a declared constructor has several methods that could be one (resolve_class_constructor, which first picks each block’s rendering).