xtask: unit-factors report of literal conversion factors outside the unit table

Part of #579. Lists float literals equal to common conversion factors
(1e-3, 1e6, 273.15, 25.4, 9.81, …) outside crates/model/src/units; report
only, so later steps can drive it to zero before it becomes a CI check.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

xtask/src/main.rs

@@ -13,6 +13,7 @@ mod layers;
 mod licences;
 mod skill;
 mod test;
+mod unit_factors;
 
 use std::path::{Path, PathBuf};
 use std::process::{Command, ExitCode};
@@ -53,6 +54,8 @@ commands:
                   and the flags CI plans its jobs with: everything (manifest, lock file,
                   toolchain, xtask or workflows changed), solver (the heavy tests or the oracle
                   are affected), wasm (a crate the wasm check builds is affected)
+  unit-factors    report literal unit-conversion factors (1e-3, 1e6, 273.15, 25.4, …) written
+                  outside the unit table, crates/model/src/units (report only, #579)
   wasm            cargo check every library crate and the web app for wasm32-unknown-unknown
   ci [--affected REV]
                   fmt --check, assets, layers, clippy -D warnings, then the tests
@@ -102,6 +105,7 @@ fn main() -> ExitCode {
             c.args(["run", "--release", "-p", affected::ORACLE_PACKAGE, "--bin", "oracle", "--"]).args(&rest);
             run(c, "oracle")
         }
+        Some("unit-factors") => unit_factors::run(&root()),
         Some("wasm") => cmd_wasm(),
         Some("-h" | "--help" | "help") | None => {
             print!("{USAGE}");

xtask/src/unit_factors.rs

@@ -0,0 +1,134 @@
+//! `cargo xtask unit-factors`: report literal unit-conversion factors (1e-3, 1e6, 273.15, 25.4, …)
+//! written outside the unit table (`crates/model/src/units/`).
+//!
+//! Issue #579 routes every conversion through the table. Until the later steps have removed the
+//! existing factors this is a report and never fails; once the count is zero it becomes a CI check.
+//! Many hits are tolerances or algorithm constants rather than conversions: the report lists them
+//! all so each can be classified.
+
+use std::path::Path;
+
+/// The factors flagged, with what each usually converts.
+const FACTORS: &[(f64, &str)] = &[
+    (1e-3, "milli (mm↔m, ms↔s, g↔kg)"),
+    (1e3, "kilo (t↔kg, m↔mm)"),
+    (1e6, "mega (MPa↔Pa, mm²↔m²)"),
+    (1e9, "giga (GPa↔Pa, mm³↔m³)"),
+    (1e-6, "micro (Pa↔MPa)"),
+    (1e-9, "nano (Pa↔GPa, m³↔mm³)"),
+    (1e12, "t/mm³↔kg/m³"),
+    (1e-12, "kg/m³↔t/mm³"),
+    (273.15, "°C↔K"),
+    (459.67, "°F↔°R"),
+    (25.4, "in↔mm"),
+    (0.0254, "in↔m"),
+    (9.80665, "standard gravity"),
+    (9.81, "gravity"),
+    (9810.0, "gravity in mm/s²"),
+];
+
+/// The one place factors belong.
+const TABLE: &str = "crates/model/src/units/";
+const SKIP_DIRS: &[&str] = &["target", ".git", "plan", "dist", "xtask", "tests", "node_modules"];
+
+pub fn run(root: &Path) -> Result<(), String> {
+    let mut files = Vec::new();
+    for dir in ["crates", "apps"] {
+        walk(&root.join(dir), &mut files);
+    }
+    files.sort();
+    let mut hits = Vec::new();
+    for path in &files {
+        let rel = path.strip_prefix(root).unwrap_or(path).to_string_lossy().replace('\\', "/");
+        if rel.starts_with(TABLE) {
+            continue;
+        }
+        let Ok(text) = std::fs::read_to_string(path) else { continue };
+        for (n, line) in text.lines().enumerate() {
+            // Unit tests sit at the end of a file behind `#[cfg(test)]`; their values are data.
+            if line.trim_start().starts_with("#[cfg(test)]") {
+                break;
+            }
+            let code = line.split("//").next().unwrap_or("");
+            for value in literals(code) {
+                if let Some((_, what)) = FACTORS.iter().find(|(f, _)| *f == value) {
+                    hits.push(format!("{rel}:{}: {value:e} ({what}): {}", n + 1, line.trim()));
+                }
+            }
+        }
+    }
+    for h in &hits {
+        println!("{h}");
+    }
+    println!("unit-factors: {} literal factor(s) outside {TABLE} (report only; #579 drives this to zero)", hits.len());
+    Ok(())
+}
+
+fn walk(dir: &Path, out: &mut Vec<std::path::PathBuf>) {
+    let Ok(rd) = std::fs::read_dir(dir) else { return };
+    for e in rd.flatten() {
+        let p = e.path();
+        let name = e.file_name().to_string_lossy().to_string();
+        if p.is_dir() {
+            if !SKIP_DIRS.contains(&name.as_str()) && !name.starts_with('.') {
+                walk(&p, out);
+            }
+        } else if p.extension().is_some_and(|x| x == "rs") {
+            out.push(p);
+        }
+    }
+}
+
+/// The floating-point literals on a line of code, parsed (`1_000.0`, `1e-3`,
+/// `273.15_f64`). Digits inside identifiers (`vec3`) are skipped.
+fn literals(code: &str) -> Vec<f64> {
+    let chars: Vec<char> = code.chars().collect();
+    let mut out = Vec::new();
+    let mut i = 0;
+    while let Some(&c) = chars.get(i) {
+        let prev_ident = i > 0 && chars.get(i - 1).is_some_and(|p| p.is_alphanumeric() || *p == '_' || *p == '.');
+        if !c.is_ascii_digit() || prev_ident {
+            i += 1;
+            continue;
+        }
+        let start = i;
+        while let Some(&d) = chars.get(i) {
+            let exp_sign = matches!(d, '+' | '-') && matches!(chars.get(i.wrapping_sub(1)), Some('e' | 'E'));
+            if d.is_ascii_digit() || d == '_' || d == '.' || d == 'e' || d == 'E' || exp_sign {
+                // `0..n` is a range, `1.max(x)` a method call: stop at a dot not followed by a digit.
+                if d == '.' && !chars.get(i + 1).is_some_and(char::is_ascii_digit) {
+                    break;
+                }
+                i += 1;
+            } else {
+                break;
+            }
+        }
+        let text: String = chars.get(start..i).unwrap_or_default().iter().filter(|c| **c != '_').collect();
+        let suffix_start = i;
+        // Skip a type suffix (`f64`, `_f32`, `u8`).
+        while chars.get(i).is_some_and(|c| c.is_alphanumeric() || *c == '_') {
+            i += 1;
+        }
+        let suffix: String = chars.get(suffix_start..i).unwrap_or_default().iter().collect();
+        // Conversions are floating-point arithmetic; integer literals are counts and caps.
+        let float = text.contains(['.', 'e', 'E']) || suffix.trim_start_matches('_').starts_with('f');
+        if float && let Ok(v) = text.parse::<f64>() {
+            out.push(v);
+        }
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::literals;
+
+    #[test]
+    fn literals_on_a_line() {
+        assert_eq!(literals("let x = 1e-3 * y + 273.15_f64;"), vec![1e-3, 273.15]);
+        assert_eq!(literals("for i in 0..1000 { vec3(1_000.0) }"), vec![1000.0]);
+        assert_eq!(literals("a.max(1.0e6) - 2.max(b)"), vec![1e6]);
+        assert_eq!(literals("t.0 + x1 + 25.4f32 + 3f64"), vec![25.4, 3.0]);
+    }
+}