Do not run codegen in build.rs scripts (#3874)

### What
Running codegen from our `build.rs` was a problem, because it required
specific versions of specific tools to be installed (`clang-format`,
`black`, etc). It is better to run the codegen with `just codegen`,
which will ensure the correct tools are installed via `pixi`.

With this PR you now have to run `just codegen` manually each time you
change `re_types_builder` or any `.fbs`. If you forget to do so, the CI
will catch it for you.

This PR removes `crates/re_types/build.rs`, but does NOT touch
`crates/re_types_builder/build.rs`.

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/3874) (if
applicable)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG

- [PR Build Summary](https://build.rerun.io/pr/3874)
- [Docs
preview](https://rerun.io/preview/fdfd159d5b2d8f7a089d3b69d05b2a6c33c24a2b/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/fdfd159d5b2d8f7a089d3b69d05b2a6c33c24a2b/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://ref.rerun.io/dev/bench/)
- [Wasm size tracking](https://ref.rerun.io/dev/sizes/)

Author: emilk

.github/workflows/contrib_checks.yml

@@ -92,6 +92,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: codegen
+          args: --force
 
       - name: No Diffs From Running Codegen
         run: |

.github/workflows/reusable_checks.yml

@@ -134,6 +134,7 @@ jobs:
         uses: actions-rs/cargo@v1
         with:
           command: codegen
+          args: --force
 
       - name: No Diffs From Running Codegen
         run: |

crates/re_types/Cargo.toml

@@ -45,13 +45,6 @@ serde = ["dep:serde", "re_string_interner/serde"]
 ## Only useful for testing purposes.
 testing = []
 
-## Special hack!
-##
-## If you configure rust-analyzer to set `--all-features,
-## then this feature will be set and that will ensure that
-## `rust-analyzer` won't run the (expensive) `build.rs`!
-__opt_out_of_auto_rebuild = []
-
 
 [dependencies]
 # Rerun

crates/re_types/README.md

@@ -10,3 +10,5 @@ Part of the [`rerun`](https://github.com/rerun-io/rerun) family of crates.
 The standard Rerun data types, component types, and archetypes.
 
 This crate includes both the language-agnostic definitions (flatbuffers IDL) as well as the generated code.
+
+Generated the code with `just codegen`.

crates/re_types/build.rs

@@ -10,4 +10,5 @@ Part of the [`rerun`](https://github.com/rerun-io/rerun) family of crates.
 This crate implements Rerun's code generation tools.
 
 These tools translate language-agnostic IDL definitions (flatbuffers) into code.
-They are invoked from `re_types`' build script (`build.rs`).
+
+You can generate the code with `just codegen`.

crates/re_types_builder/README.md

@@ -1,12 +1,15 @@
-//! Helper binary for running the codegen manually. Useful during development!
+//! This binary runs the codegen manually.
+//!
+//! It is easiest to call this using `just codegen`,
+//! which will set up the necessary tools.
 
-use camino::Utf8Path;
 use re_build_tools::{
     read_versioning_hash, set_output_cargo_build_instructions, write_versioning_hash,
 };
-use re_types_builder::{compute_re_types_builder_hash, compute_re_types_hash, SourceLocations};
+use re_types_builder::{compute_re_types_hash, SourceLocations};
+
+use camino::Utf8Path;
 
-const RE_TYPES_BUILDER_SOURCE_HASH_PATH: &str = "crates/re_types_builder/source_hash.txt";
 const RE_TYPES_SOURCE_HASH_PATH: &str = "crates/re_types/source_hash.txt";
 const DEFINITIONS_DIR_PATH: &str = "crates/re_types/definitions";
 const ENTRYPOINT_PATH: &str = "crates/re_types/definitions/rerun/archetypes.fbs";
@@ -31,6 +34,7 @@ macro_rules! join {
 
 fn main() {
     re_log::setup_native_logging();
+
     // This isn't a build.rs script, so opt out of cargo build instrctinsr
     set_output_cargo_build_instructions(false);
 
@@ -40,13 +44,17 @@ fn main() {
         .unwrap();
 
     let mut profiler = re_tracing::Profiler::default();
+    let mut always_run = false;
 
     for arg in std::env::args().skip(1) {
         match arg.as_str() {
             "--help" => {
-                println!("Usage: [--help] [--profile]");
+                println!("Usage: [--help] [--force] [--profile]");
                 return;
             }
+            "--force" => {
+                always_run = true;
+            }
             "--profile" => profiler.start(),
             _ => {
                 eprintln!("Unknown argument: {arg:?}");
@@ -61,28 +69,41 @@ fn main() {
         .unwrap();
 
     let re_types_source_hash_path = workspace_dir.join(RE_TYPES_SOURCE_HASH_PATH);
-    let re_types_builder_source_hash_path = workspace_dir.join(RE_TYPES_BUILDER_SOURCE_HASH_PATH);
     let definitions_dir_path = workspace_dir.join(DEFINITIONS_DIR_PATH);
     let entrypoint_path = workspace_dir.join(ENTRYPOINT_PATH);
-    let doc_examples_dir_path = workspace_dir.join(DOC_EXAMPLES_DIR_PATH);
     let cpp_output_dir_path = workspace_dir.join(CPP_OUTPUT_DIR_PATH);
     let rust_output_dir_path = workspace_dir.join(RUST_OUTPUT_DIR_PATH);
     let python_output_dir_path = workspace_dir.join(PYTHON_OUTPUT_DIR_PATH);
     let python_testing_output_dir_path = workspace_dir.join(PYTHON_TESTING_OUTPUT_DIR_PATH);
     let docs_content_dir_path = workspace_dir.join(DOCS_CONTENT_DIR_PATH);
 
     let cur_hash = read_versioning_hash(&re_types_source_hash_path);
-    eprintln!("cur_hash: {cur_hash:?}");
-
-    let builder_hash = compute_re_types_builder_hash();
+    re_log::debug!("cur_hash: {cur_hash:?}");
 
     let new_hash = compute_re_types_hash(&SourceLocations {
-        definitions_dir: definitions_dir_path.as_str(),
-        doc_examples_dir: doc_examples_dir_path.as_str(),
-        python_output_dir: python_output_dir_path.as_str(),
-        cpp_output_dir: cpp_output_dir_path.as_str(),
+        definitions_dir: DEFINITIONS_DIR_PATH,
+        doc_examples_dir: DOC_EXAMPLES_DIR_PATH,
+        python_output_dir: PYTHON_OUTPUT_DIR_PATH,
+        cpp_output_dir: CPP_OUTPUT_DIR_PATH,
     });
 
+    if let Some(cur_hash) = cur_hash {
+        if cur_hash == new_hash {
+            if always_run {
+                re_log::info!(
+                    "The hash hasn't changed, but --force was passed, so we'll run anyway."
+                );
+            } else {
+                re_log::info!("Returning early: no changes detected (and --force wasn't set).");
+                return;
+            }
+        } else {
+            re_log::info!("Change detected");
+        }
+    } else {
+        re_log::info!("Missing {re_types_source_hash_path:?} (first time running codegen)");
+    }
+
     re_log::info!("Running codegen…");
     let (report, reporter) = re_types_builder::report::init();
 
@@ -121,7 +142,6 @@ fn main() {
     report.finalize();
 
     write_versioning_hash(re_types_source_hash_path, new_hash);
-    write_versioning_hash(re_types_builder_source_hash_path, builder_hash);
 
     re_log::info!("Done.");
 }

crates/re_types_builder/src/bin/build_re_types.rs

@@ -328,12 +328,12 @@ pub fn compute_re_types_hash(locations: &SourceLocations<'_>) -> String {
         &cpp_extensions_hash,
     ]);
 
-    eprintln!("re_types_builder_hash: {re_types_builder_hash:?}");
-    eprintln!("definitions_hash: {definitions_hash:?}");
-    eprintln!("doc_examples_hash: {doc_examples_hash:?}");
-    eprintln!("python_extensions_hash: {python_extensions_hash:?}");
-    eprintln!("cpp_extensions_hash: {cpp_extensions_hash:?}");
-    eprintln!("new_hash: {new_hash:?}");
+    re_log::debug!("re_types_builder_hash: {re_types_builder_hash:?}");
+    re_log::debug!("definitions_hash: {definitions_hash:?}");
+    re_log::debug!("doc_examples_hash: {doc_examples_hash:?}");
+    re_log::debug!("python_extensions_hash: {python_extensions_hash:?}");
+    re_log::debug!("cpp_extensions_hash: {cpp_extensions_hash:?}");
+    re_log::debug!("new_hash: {new_hash:?}");
 
     new_hash
 }