[PR] THRIFT-6026: Add Mermaid diagram generator (--gen mmd) [thrift]

["Jens-G (via GitHub)" <gi...@apache.org>]

Jens-G opened a new pull request, #3524:
URL: https://github.com/apache/thrift/pull/3524

   Client: mmd
   
   Adds t_mmd_generator producing Mermaid classDiagram output from a Thrift IDL file. Renders natively on GitHub, GitLab, Confluence and similar platforms without external tooling.
   
   - All IDL constructs mapped: enum <<enumeration>>, struct, union, exception, typedef, service with method signatures
   - Service extends rendered as inheritance arrows (--|>)
   - Container generics use tilde syntax (list~T~, map~K,V~)
   - Optional :exceptions flag for dashed exception dependency arrows
   - -r flag aggregates all included programs into a single diagram
   - Constants omitted (no structural value in a type diagram)
   - Output in gen-mmd/<programname>.mmd
   
   


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Re: [PR] THRIFT-6026: Add Mermaid diagram generator (--gen mmd) [thrift]

["Jens-G (via GitHub)" <gi...@apache.org>]

Jens-G commented on PR #3524:
URL: https://github.com/apache/thrift/pull/3524#issuecomment-4529523559

   ### Code review
   
   Found 5 issues:
   
   1. Typo `mmdv` in test invocation — should be `--gen mmd` to match the registered generator name; `make check` will always fail with "Unable to get a generator for: mmdv"
   
   https://github.com/apache/thrift/blob/af5b0c6eaf970f4e16ec4a76875ce887191035b1/test/Makefile.am#L105-L109
   
   2. `compiler/cpp/Makefile.am` not updated — `t_mmd_generator.cc` is added to `CMakeLists.txt` and `compiler.vcxproj` but missing from `Makefile.am`; autotools builds (`./configure && make`) will not compile the generator (every other generator including the recently-added markdown one is listed in all three build files)
   
   https://github.com/apache/thrift/blob/af5b0c6eaf970f4e16ec4a76875ce887191035b1/compiler/cpp/CMakeLists.txt#L99-L102
   
   3. Broken `-r` behavior — `main.cc` calls `generate_program()` on every included program individually, all with `get_recursive() == true`; the `generate_program()` override then calls `emit_types_recursive()` which re-emits types from those already-processed includes, producing duplicate class definitions in each intermediate `.mmd` file; the comment "a single output file" is also incorrect (one file per program is still produced)
   
   https://github.com/apache/thrift/blob/af5b0c6eaf970f4e16ec4a76875ce887191035b1/compiler/cpp/src/thrift/generate/t_mmd_generator.cc#L93-L120
   
   4. `emit_types_recursive` has no visited-set guard — with a diamond include (A → {B, C}, both → D), `emit_program_types(D)` is called twice, producing duplicate class definitions; Mermaid treats duplicate class names as a parse error
   
   https://github.com/apache/thrift/blob/af5b0c6eaf970f4e16ec4a76875ce887191035b1/compiler/cpp/src/thrift/generate/t_mmd_generator.cc#L113-L121
   
   5. `"md": "Markdown"` added to `build/generate-changes.py` — this entry belongs to a separate Markdown-extension branch and appears to be an unintentional rebase artifact in this Mermaid PR
   
   https://github.com/apache/thrift/blob/af5b0c6eaf970f4e16ec4a76875ce887191035b1/build/generate-changes.py#L156-L161
   
   🤖 Generated with [Claude Code](https://claude.ai/code)
   
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Re: [PR] THRIFT-6026: Add Mermaid diagram generator (--gen mmd) [thrift]

["Jens-G (via GitHub)" <gi...@apache.org>]

Jens-G merged PR #3524:
URL: https://github.com/apache/thrift/pull/3524


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