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fix(ino): generated prototypes are inserted above the sketch's own #includes and type definitions #1196
Description
Split out of #1076 (flagged in the ".ino.prelude.h direction update" comment as worth its own child issue — it affects real builds today, IDE aside).
Problem
preprocess_ino_files (crates/fbuild-build-engine/src/source_scanner.rs, prototype block emitted before the concatenated sketch text) writes all auto-generated function prototypes above the user's own #includes and type definitions. A sketch that defines a type and then a function taking it:
#include "helpers.h"
struct MyStruct { int x; };
void draw(MyStruct s) { /* ... */ }gets void draw(MyStruct s); emitted before struct MyStruct exists → compile error in the generated .ino.cpp.
arduino-cli avoids this by inserting prototypes after the include block. Note the interaction with #1076's prelude design: the IDE prelude header is currently defined as the machine-written top half (Arduino.h + prototypes) -include'd ahead of the raw .ino — moving prototypes below the include block changes what the prelude can contain for affected sketches, so the fix needs to keep the build artifact and the IDE prelude in agreement (editor and compiler must keep seeing identical translation units).
Acceptance
- A sketch with a user-defined type used in a later function's signature compiles (prototype lands after the declarations it needs, matching arduino-cli placement).
- The IDE-flavored compile DB / prelude stays in parity:
clangd --check=<sketch.ino>reports the same diagnostics as compiling the generated.ino.cpp. - Regression tests for both single-tab and multi-tab layouts.
Parent: #1076 (Phase 0 follow-up).
Activity
feat(ide): clangd/compile-DB foundations for fbuild ide (#1076 Phase …
zackees commentedon Jul 27, 2026
Research update — revising the drafted acceptance criteria before implementing.
The original acceptance said to match arduino-cli's placement (prototypes after the include block). Verified against arduino-cli upstream: arduino-cli does not solve this class — prototypes referencing sketch-defined types still land before the type declaration there too, producing spurious compile failures that remain open bugs (arduino-cli#2161, arduino-cli#2977, related #2931/#1800), with "move the type to a .h file or add a manual prototype" as the documented workaround. Matching their placement would import their bug class, and any placement below the sketch's own leading code breaks the #1076 prelude design's load-bearing invariant (the machine-written text must be a pure prefix so
-x c++ -include <prelude>+ the raw.inoreproduces the exact build translation unit for clangd).Chosen approach instead: keep prototype insertion at the top (prelude prefix-property and editor/build parity untouched), and skip generating any prototype whose signature references a sketch-defined type (struct/class/enum/union/typedef/using names declared in the concatenated sketch text — detected with the existing tree-sitter parse). Result:
clangd --checkparity holds by construction);Revised acceptance:
.ino.cppand<stem>.ino.prelude.h).fix(ino): skip auto-prototypes referencing sketch-defined types (#1196)…