adressing PR comments

crates/re_types_builder/build.rs

@@ -3,8 +3,7 @@
 use xshell::{cmd, Shell};
 
 use re_build_tools::{
-    compute_file_hash, is_tracked_env_var_set, read_versioning_hash, rerun_if_changed,
-    rerun_if_changed_or_doesnt_exist, write_versioning_hash,
+    compute_file_hash, is_tracked_env_var_set, read_versioning_hash, write_versioning_hash,
 };
 
 // ---
@@ -33,9 +32,14 @@ fn main() {
         return;
     }
 
-    rerun_if_changed_or_doesnt_exist(SOURCE_HASH_PATH);
-    rerun_if_changed(FBS_REFLECTION_DEFINITION_PATH);
-
+    // We're building an actual build graph here, and Cargo has no idea about it.
+    //
+    // Worse: some nodes in our build graph actually output artifacts into the src/ directory,
+    // which Cargo always interprets as "need to rebuild everything ASAP", leading to an infinite
+    // feedback loop.
+    //
+    // For these reasons, we manually compute and track signature hashes for the graph nodes we
+    // depend on, and make sure to exit early if everything's already up to date.
     let cur_hash = read_versioning_hash(SOURCE_HASH_PATH);
     let new_hash = compute_file_hash(FBS_REFLECTION_DEFINITION_PATH);
 

crates/re_types_builder/definitions/reflection.fbs

@@ -1,3 +1,6 @@
+// Copied verbatim from the official flatbuffers source tree:
+// https://github.com/google/flatbuffers/blob/63b7b25289447313ab6e79191fa1733748dca0da/reflection/reflection.fbs
+
 // This schema defines objects that represent a parsed schema, like
 // the binary version of a .fbs file.
 // This could be used to operate on unknown FlatBuffers at runtime.

crates/re_types_builder/source_hash.txt

@@ -1,4 +1,4 @@
 # This is a sha256 hash for all direct and indirect dependencies of this crate's build script.
 # It can be safely removed at anytime to force the build script to run again.
 # Check out build.rs to see how it's computed.
-72d936d50287d6c16d0c1b91f86bd74120642c8fc08e885f08dd2b92bb52e8a4
+674450e64722effea9b29a84c34fab81b9d57497136a8f161561b8e19f7441b2

crates/re_types_builder/src/arrow_registry.rs

@@ -4,12 +4,7 @@ use anyhow::Context as _;
 use arrow2::datatypes::{DataType, Field, UnionMode};
 use std::collections::{BTreeMap, HashMap};
 
-use crate::{ElementType, Object, Type};
-
-// ---
-
-pub const ARROW_ATTR_TRANSPARENT: &str = "arrow.attr.transparent";
-pub const ARROW_ATTR_SPARSE_UNION: &str = "arrow.attr.sparse_union";
+use crate::{ElementType, Object, Type, ARROW_ATTR_SPARSE_UNION, ARROW_ATTR_TRANSPARENT};
 
 // --- Registry ---
 
@@ -59,7 +54,7 @@ impl ArrowRegistry {
         let num_fields = obj.fields.len();
 
         assert!(
-            !(is_transparent && (!is_struct || num_fields != 1)),
+            !is_transparent || (is_struct && num_fields == 1),
             "cannot have a transparent arrow object with any number of fields but 1: {:?} has {num_fields}",
             obj.fqname,
         );

crates/re_types_builder/src/codegen/common.rs

@@ -39,3 +39,22 @@ pub fn quote_doc_from_docs(docs: &Docs, tags: &[&str]) -> Vec<String> {
 
     lines
 }
+
+pub trait StringExt {
+    fn push_text(&mut self, text: impl AsRef<str>, linefeeds: usize, indent: usize) -> &mut Self;
+    fn push_unindented_text(&mut self, text: impl AsRef<str>, linefeeds: usize) -> &mut Self;
+}
+
+impl StringExt for String {
+    fn push_text(&mut self, text: impl AsRef<str>, linefeeds: usize, indent: usize) -> &mut Self {
+        self.push_str(&indent::indent_all_by(indent, text.as_ref()));
+        self.push_str(&vec!["\n"; linefeeds].join(""));
+        self
+    }
+
+    fn push_unindented_text(&mut self, text: impl AsRef<str>, linefeeds: usize) -> &mut Self {
+        self.push_str(&unindent::unindent(text.as_ref()));
+        self.push_str(&vec!["\n"; linefeeds].join(""));
+        self
+    }
+}

crates/re_types_builder/src/codegen/mod.rs

@@ -15,14 +15,10 @@ pub trait CodeGenerator {
 pub const AUTOGEN_WARNING: &str =
     "NOTE: This file was autogenerated by re_types_builder; DO NOT EDIT.";
 
-pub const RERUN_ATTR_COMPONENT_REQUIRED: &str = "rerun.attr.component_required";
-pub const RERUN_ATTR_COMPONENT_RECOMMENDED: &str = "rerun.attr.component_recommended";
-pub const RERUN_ATTR_COMPONENT_OPTIONAL: &str = "rerun.attr.component_optional";
-
 // ---
 
 mod common;
-use self::common::quote_doc_from_docs;
+use self::common::{quote_doc_from_docs, StringExt};
 
 mod python;
 mod rust;