bitflicker64 commented on code in PR #359:
URL: 
https://github.com/apache/hugegraph-computer/pull/359#discussion_r3910387315


##########
computer-rust/src/fixtures/tolerance.rs:
##########
@@ -0,0 +1,100 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+pub struct DifferentialTolerance;

Review Comment:
   ⚠️ `DifferentialTolerance` is a fieldless struct whose only job is to be a 
namespace for two functions, and the module is already that namespace. `grep 
-rn 'DifferentialTolerance' computer-rust/` returns the declaration, the 
`impl`, and six calls, all six inside this file's own `#[cfg(test)]` block. 
Nothing in `kernel/`, `ffi/`, or `benches/` touches it.
   
   Not asking you to drop the file, since #355 lists correctness fixtures as a 
work item. Just drop the wrapper:
   
   ```rust
   pub fn l1_distance(actual: &[f64], expected: &[f64]) -> Result<f64, String> 
{ .. }
   pub fn assert_parity(actual: &[f64], expected: &[f64], epsilon: f64) -> 
Result<(), String> { .. }
   ```
   
   Callers become `tolerance::assert_parity(..)`, which reads better than 
`DifferentialTolerance::assert_parity(..)` anyway. While you are in here: 
`assert_parity` (lines 48-60) re-implements the length-mismatch check and the 
per-element finite check from `l1_distance` (lines 21-33), copied `format!` 
strings and all. Have one call into the other's guard instead of carrying a 
second copy.



##########
computer-rust/src/fixtures/dataset.rs:
##########
@@ -0,0 +1,109 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use crate::kernel::csr::CsrGraph;
+
+pub struct GraphFixture {
+    pub name: String,
+    pub num_vertices: u32,
+    pub edges: Vec<(u32, u32, f64)>,
+}
+
+impl GraphFixture {
+    /// Returns the Zachary's Karate Club representative graph dataset fixture.
+    pub fn karate_club() -> Self {

Review Comment:
   ⚠️ This is not Zachary's karate club. The real graph has 34 vertices and 78 
edges; this list has 35, and every one of them has source 0, 1, 2, or 3, 
stopping part-way through vertex 3's row. Counting at head, the vertices 
appearing at either endpoint are `{0..13, 17, 19, 21, 27, 28, 30, 31, 32}`, so 
twelve vertices have no incident edge, including vertex 33, which is one of the 
two hubs the dataset is known for.
   
   That matters given what the fixture is for. #355 requires differential 
parity against ground truth, and `docs/rust-modernization-roadmap.md` in this 
PR promises L1 distance <= 1e-6 against ground-truth outputs. A parity test 
comparing this kernel's PageRank against a Java or NetworkX run on the real 
karate club will disagree on every vertex, and whoever hits it first will go 
hunting for a bug in the kernel.
   
   Either paste the full 78-edge list, or rename to something that does not 
claim to be the canonical dataset (`karate_club_subset`, or just fold it into 
`synthetic_*`).



##########
computer-rust/src/ffi/c_api.rs:
##########
@@ -0,0 +1,217 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#![allow(clippy::not_unsafe_ptr_arg_deref)]
+
+use crate::kernel::csr::CsrGraph;
+use crate::kernel::pagerank::PageRankKernel;
+use crate::RUST_KERNEL_VERSION;
+use std::ffi::CString;
+use std::os::raw::c_char;
+use std::slice;
+use std::sync::OnceLock;
+
+pub struct GraphBuilder {
+    num_vertices: u32,
+    edges: Vec<(u32, u32, f64)>,
+    csr: Option<CsrGraph>,
+}
+
+#[no_mangle]
+pub extern "C" fn computer_graph_create(num_vertices: u32) -> *mut 
GraphBuilder {
+    let builder = Box::new(GraphBuilder {
+        num_vertices,
+        edges: Vec::new(),
+        csr: None,
+    });
+    Box::into_raw(builder)
+}
+
+#[no_mangle]
+pub extern "C" fn computer_graph_add_edge(
+    handle: *mut GraphBuilder,
+    src: u32,
+    dst: u32,
+    weight: f64,
+) -> i32 {
+    if handle.is_null() {
+        return -1;
+    }
+    let builder = unsafe { &mut *handle };
+    if builder.csr.is_some() {
+        return -2;
+    }
+    if src >= builder.num_vertices || dst >= builder.num_vertices {
+        return -1;
+    }
+    if weight < 0.0 || !weight.is_finite() {
+        return -1;
+    }
+    builder.edges.push((src, dst, weight));
+    0
+}
+
+#[no_mangle]
+pub extern "C" fn computer_graph_finalize(handle: *mut GraphBuilder) -> i32 {
+    if handle.is_null() {
+        return -1;
+    }
+    let builder = unsafe { &mut *handle };
+    let csr = CsrGraph::from_edges(builder.num_vertices, &builder.edges);
+    builder.csr = Some(csr);
+    0
+}
+
+#[no_mangle]
+pub extern "C" fn computer_graph_compute_pagerank(
+    handle: *const GraphBuilder,
+    damping_factor: f64,
+    max_iterations: u32,
+    tolerance: f64,
+    out_scores: *mut f64,
+    out_capacity: u32,
+) -> i32 {
+    if handle.is_null() || out_scores.is_null() {
+        return -1;
+    }
+    let builder = unsafe { &*handle };
+    let csr = match &builder.csr {
+        Some(c) => c,
+        None => return -2,
+    };
+
+    if out_capacity < csr.num_vertices() {
+        return -3;
+    }
+
+    if !damping_factor.is_finite() || damping_factor < 0.0 || damping_factor > 
1.0 {
+        return -4;
+    }
+    if !tolerance.is_finite() || tolerance < 0.0 {
+        return -4;
+    }
+
+    let kernel = PageRankKernel::new(damping_factor, max_iterations, 
tolerance);

Review Comment:
   ⚠️ These six lines are a character-for-character copy of the two checks 
already inside `PageRankKernel::try_new` (pagerank.rs:33-44). They only exist 
because line 108 calls `PageRankKernel::new`, which is 
`try_new(..).expect(..)`, so without the pre-check a bad parameter panics 
instead of returning `-4`.
   
   Worth collapsing now rather than in Phase 3, for a reason beyond line count: 
`Cargo.toml` sets `panic = "abort"` on the release profile. A `pub extern "C"` 
function that can reach a `panic!` in a `panic = "abort"` cdylib does not 
unwind and does not return an error code, it takes the host process with it. 
The roadmap puts a JVM and a Go runtime on the other side of this boundary, so 
the panicking constructor is the thing to delete before that lands.
   
   Drop lines 101-106 and line 108 in favour of:
   
   ```rust
   let kernel = match PageRankKernel::try_new(damping_factor, max_iterations, 
tolerance) {
       Ok(k) => k,
       Err(_) => return -4,
   };
   ```
   
   Then delete `PageRankKernel::new` (pagerank.rs:52-55) entirely. Its only 
other callers are `benches/kernel_bench.rs:25` and two unit tests, all of which 
become `try_new(..).unwrap()`. The duplicate is also the usual drift bug: add a 
third constraint to `try_new` and the C-ABI quietly stops enforcing it.



##########
computer-rust/src/kernel/csr.rs:
##########
@@ -0,0 +1,138 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#[derive(Debug, Clone, Default)]
+pub struct Edge {

Review Comment:
   🧹 Three dead public symbols, each verified by grep at head as returning only 
its own definition. `dead_code` will not warn on any of them because they are 
`pub` in a library crate, so CI stays green while they rot.
   
   - `Edge` (this line): exactly one occurrence in the crate. `out_edges` 
returns `(&[u32], &[f64])` and never constructs it.
   - `CsrGraph::new` (lines 33-41): zero call sites. `from_edges` is the only 
constructor anything uses and builds `row_offsets` itself.
   - `GraphFixture.name` (`fixtures/dataset.rs:21`): written by both 
constructors, including a `format!` allocation in `synthetic_powerlaw`, never 
read.
   
   Deleting all three is a smaller crate with no behaviour change. Add them 
back in the PR that has a caller.



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