feat: Add separate report for public function bytecode sizes (#8750)

Re-use https://github.com/noir-lang/noir-gates-diff for computing
bytecode sizes of all public functions. I made a new script
`noir-projects/noir-contracts/publicFunctionsSizeReport.js`. It runs
through all the artifacts in the `target` directory of `noir-contracts`
and collects all public functions. We then compare a report of bytecode
sizes based upon the package name of
`{contract_name}::{public_function_name}`.

To see an example of the sticky comment after a public function change
you can look at
#8755.

.github/workflows/ci.yml

@@ -696,6 +696,47 @@ jobs:
           delete: ${{ !steps.gates_diff.outputs.markdown }}
           message: ${{ steps.gates_diff.outputs.markdown }}
 
+  public-functions-size-report:
+    needs: [build-images, changes]
+    if: needs.changes.outputs.non-docs == 'true' && needs.changes.outputs.non-misc-ci == 'true'
+    runs-on: ${{ github.event.pull_request.user.login || github.actor }}-x86
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/checkout@v4
+        with: { ref: "${{ env.GIT_COMMIT }}" }
+      # Only allow one memory-hunger prover test to use this runner
+      - uses: ./.github/ci-setup-action
+        with:
+          concurrency_key: public-functions-size-report-x86
+      - name: "Aztec Public Functions Bytecode Size Report"
+        working-directory: ./noir-projects/
+        timeout-minutes: 40
+        run: |
+          earthly-ci \
+          --artifact +public-functions-report/public_functions_report.json
+          mv public_functions_report.json ../public_functions_report.json
+
+      - name: Compare public functions bytecode size reports
+        id: public_functions_sizes_diff
+        uses: noir-lang/noir-gates-diff@ef8aaf48fb833f3b6e3f91665bb23afb7e68c6e3
+        with:
+          report: public_functions_report.json
+          header: |
+            # Changes to public function bytecode sizes
+          brillig_report: true
+          brillig_report_bytes: true
+          summaryQuantile: 0 # Display any diff in bytecode size count
+
+      - name: Add bytecode size diff to sticky comment
+        if: github.event_name == 'pull_request' || github.event_name == 'pull_request_target'
+        uses: marocchino/sticky-pull-request-comment@v2
+        with:
+          header: public_functions_size
+          # delete the comment in case changes no longer impact circuit sizes
+          delete: ${{ !steps.public_functions_sizes_diff.outputs.markdown }}
+          message: ${{ steps.public_functions_sizes_diff.outputs.markdown }}
+
   merge-check:
     runs-on: ubuntu-20.04
     needs:

noir-projects/Earthfile

@@ -124,3 +124,12 @@ gates-report:
   RUN ./gates_report.sh
 
   SAVE ARTIFACT ./noir-protocol-circuits/gates_report.json gates_report.json
+
+public-functions-report:
+  FROM +build-contracts
+  WORKDIR /usr/src/noir-projects
+
+  RUN cd noir-contracts && node publicFunctionsSizeReport.js ./target/
+
+  SAVE ARTIFACT ./noir-contracts/public_functions_report.json public_functions_report.json
+

noir-projects/noir-contracts/publicFunctionsSizeReport.js

@@ -0,0 +1,73 @@
+const path = require("path");
+const fs = require("fs");
+const fsp = require("fs").promises;
+
+// Simple script to extract the exact bytecode size of a contracts public functions.
+// The output of this script is meant to be used with the noir-lang/noir-gates-diff project.
+// The noir-gates-diff was made for comparing ACIR/Brillig opcodes.
+// However, this script was made to re-use the noir-gates-diff for bytecode sizes as
+// to minimize both the amount of changes needed in noir-gates-diff and in nargo.
+async function main() {
+
+  let [targetDir] = process.argv.slice(2);
+  if (!targetDir) {
+    console.log(
+      "Usage: node extractPublicFunctionsAsNoirArtifacts.js <targetDir>"
+    );
+    return;
+  }
+
+  let artifactPaths = [];
+  fs.readdirSync(targetDir).forEach(file => {
+    // We want to exclude any backups that may be generated by the avm-transpiler
+    if (path.extname(file) === ".json") {
+        artifactPaths.push(path.join(targetDir, file));
+    }
+  });
+
+  let workspaceReport = {
+    programs: []
+  }
+  for (var i = 0; i < artifactPaths.length; i++) {
+    let contractArtifactPath = artifactPaths[i];
+    const contractArtifact = JSON.parse(
+        await fsp.readFile(contractArtifactPath, "utf8")
+    );
+    contractArtifact.functions.forEach(async func => {
+        if (func.custom_attributes.includes("public")) {
+            if (func.brillig_names.length != 1) {
+                console.log(
+                    "Expected only a single Brillig function"
+                );
+                return;
+            }
+            let func_with_contract_name = contractArtifact.name + "::" + func.brillig_names[0];
+            let program_report = {
+              package_name: "",
+              functions: [{ name: "main", opcodes: 1 }],
+              unconstrained_functions: [],
+            }
+            // Programs are compared by package name, so we make a unique one for each function here
+            program_report.package_name = func_with_contract_name;
+            let bytecode_bytes = Buffer.from(func.bytecode, 'base64');
+            let func_report = {
+              name: "main",
+              opcodes: bytecode_bytes,
+            };
+            func_report.opcodes = bytecode_bytes.length;
+            program_report.unconstrained_functions.push(func_report);
+            workspaceReport.programs.push(program_report);
+        }
+    });
+  }
+
+  const outPath = path.join("public_functions_report.json");
+
+  console.log(`Writing to ${outPath}`);
+  await fsp.writeFile(outPath, JSON.stringify(workspaceReport, null, 2));
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});