Port eclexiaiser validator from Python to Rust (clears banned-language governance check) (#30)

The `governance / package anti-pattern policy` check fails because org
policy fully bans Python and the repo shipped
`.github/scripts/validate_eclexiaiser.py`. Rather than add an exemption
pragma, this **ports** the validator to a dependency-free Rust program.

- **No new toolchain / Cargo project / crates** — builds with the
`rustc` preinstalled on `ubuntu-latest`. `dogfood-gate.yml` now does
`rustc -O … && ./validate` instead of `python3 …`.
- **Identical semantics** to the `tomllib` version: non-empty
`project.name`, ≥1 `[[functions]]`, non-empty `name`+`source` per
function; same messages; same "Valid: NAME (N function(s))" output.
- **Verified** locally (Debian, `rustc -D warnings`) against the real
`eclexiaiser.toml` plus fixtures covering inline comments, single-quoted
values with `#`, and the missing-name / no-functions / missing-source
failure paths.

Removes the last banned-language file, so `git ls-files '*.py'` is empty
and the policy passes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/scripts/validate_eclexiaiser.py

@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: MPL-2.0
+// Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath) <j.d.a.jewell@open.ac.uk>
+// Owner: Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+//
+// Validates eclexiaiser.toml structure (called by dogfood-gate.yml).
+//
+// Ported from validate_eclexiaiser.py — Python is banned by governance policy.
+// Dependency-free (no crates) so it builds with the preinstalled `rustc` on
+// ubuntu-latest: `rustc -O validate_eclexiaiser.rs -o validate_eclexiaiser`.
+// The checks are deliberately shallow, matching the original tomllib validator.
+
+use std::process::exit;
+
+/// Return the slice of `s` before an unquoted `#` (TOML inline comment).
+fn strip_inline_comment(s: &str) -> &str {
+    let bytes = s.as_bytes();
+    let mut quote: Option<u8> = None;
+    let mut i = 0;
+    while i < bytes.len() {
+        let c = bytes[i];
+        match quote {
+            Some(q) => {
+                if c == q {
+                    quote = None;
+                }
+            }
+            None => match c {
+                b'"' | b'\'' => quote = Some(c),
+                b'#' => return &s[..i],
+                _ => {}
+            },
+        }
+        i += 1;
+    }
+    s
+}
+
+/// Strip one layer of matching single or double quotes, if present.
+fn unquote(s: &str) -> String {
+    let t = s.trim();
+    let b = t.as_bytes();
+    if b.len() >= 2 && (b[0] == b'"' || b[0] == b'\'') && b[b.len() - 1] == b[0] {
+        t[1..t.len() - 1].to_string()
+    } else {
+        t.to_string()
+    }
+}
+
+#[derive(PartialEq)]
+enum Section {
+    Other,
+    Project,
+    Function,
+}
+
+fn main() {
+    const PATH: &str = "eclexiaiser.toml";
+    let content = match std::fs::read_to_string(PATH) {
+        Ok(c) => c,
+        Err(e) => {
+            eprintln!("ERROR: cannot read {PATH}: {e}");
+            exit(1);
+        }
+    };
+
+    let mut project_name = String::new();
+    // Each [[functions]] entry collects its own (name, source).
+    let mut functions: Vec<(String, String)> = Vec::new();
+    let mut section = Section::Other;
+
+    for raw in content.lines() {
+        let line = strip_inline_comment(raw).trim();
+        if line.is_empty() {
+            continue;
+        }
+
+        if let Some(inner) = line.strip_prefix("[[").and_then(|l| l.strip_suffix("]]")) {
+            if inner.trim() == "functions" {
+                functions.push((String::new(), String::new()));
+                section = Section::Function;
+            } else {
+                section = Section::Other;
+            }
+            continue;
+        }
+        if let Some(inner) = line.strip_prefix('[').and_then(|l| l.strip_suffix(']')) {
+            section = if inner.trim() == "project" {
+                Section::Project
+            } else {
+                Section::Other
+            };
+            continue;
+        }
+
+        let Some(eq) = line.find('=') else { continue };
+        let key = line[..eq].trim();
+        let value = unquote(&line[eq + 1..]);
+        match section {
+            Section::Project if key == "name" => project_name = value,
+            Section::Function => {
+                if let Some(f) = functions.last_mut() {
+                    match key {
+                        "name" => f.0 = value,
+                        "source" => f.1 = value,
+                        _ => {}
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+
+    if project_name.trim().is_empty() {
+        eprintln!("ERROR: project.name is required");
+        exit(1);
+    }
+    if functions.is_empty() {
+        eprintln!("ERROR: at least one [[functions]] entry is required");
+        exit(1);
+    }
+    for (name, source) in &functions {
+        if name.trim().is_empty() {
+            eprintln!("ERROR: function name cannot be empty");
+            exit(1);
+        }
+        if source.trim().is_empty() {
+            eprintln!("ERROR: function {name} has no source path");
+            exit(1);
+        }
+    }
+
+    println!(
+        "Valid: {} ({} function(s))",
+        project_name.trim(),
+        functions.len()
+    );
+}

.github/scripts/validate_eclexiaiser.rs

@@ -261,8 +261,10 @@ jobs:
 
           echo "has_manifest=true" >> "$GITHUB_OUTPUT"
 
-          # Validate TOML structure using Python 3.11+ tomllib
-          python3 .github/scripts/validate_eclexiaiser.py || {
+          # Validate TOML structure with a dependency-free Rust validator.
+          # (Python is banned by governance policy; rustc is preinstalled on ubuntu-latest.)
+          rustc -O .github/scripts/validate_eclexiaiser.rs -o "$RUNNER_TEMP/validate_eclexiaiser"
+          "$RUNNER_TEMP/validate_eclexiaiser" || {
             echo "::error file=eclexiaiser.toml::Invalid eclexiaiser.toml — see step output for details"
             exit 1
           }