From bafb9482267759eae4388a96d899553912393cbc Mon Sep 17 00:00:00 2001
From: NetterSilver <133535268+Silvertree2010@users.noreply.github.com>
Date: Thu, 15 Oct 2026 22:19:58 +0200
Subject: [PATCH] Round FormCalc Str and Format exact ties away from zero

Found while testing crates/js/src/formcalc.rs:2169 (Str) and :2258 (Format number picture)

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 crates/js/src/formcalc.rs | 11 +++++++++--
 crates/js/src/tests.rs    | 13 +++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/crates/js/src/formcalc.rs b/crates/js/src/formcalc.rs
index 059276e93..cf82eff46 100644
--- a/crates/js/src/formcalc.rs
+++ b/crates/js/src/formcalc.rs
@@ -712,6 +712,13 @@ fn num_text(n: f64) -> String {
     if s.is_empty() || s == "-0" { "0".into() } else { s.to_string() }
 }
 
+/// `v` with `decimals` places, rounding exact halves away from zero (Rust's formatter rounds them to even).
+fn fixed(v: f64, decimals: usize) -> String {
+    let k = 10f64.powi(decimals.min(20) as i32);
+    let scaled = (v * k).round() / k;
+    format!("{:.decimals$}", if scaled.is_finite() { scaled } else { v })
+}
+
 /// The number a string holds: its leading numeric part (`12abc` → 12), `None` for none.
 fn parse_num(s: &str) -> Option<f64> {
     let t = s.trim();
@@ -2166,7 +2173,7 @@ impl Interp<'_> {
                 let v = self.arg_num(args, 0)?;
                 let width = if args.len() > 1 { self.arg_num(args, 1)?.clamp(0.0, 1000.0) as usize } else { 10 };
                 let prec = if args.len() > 2 { self.arg_num(args, 2)?.clamp(0.0, 20.0) as usize } else { 0 };
-                let text = format!("{v:.prec$}");
+                let text = fixed(v, prec);
                 Val::Str(if text.len() > width { "*".repeat(width) } else { format!("{text:>width$}") })
             }
             "substr" => {
@@ -2255,7 +2262,7 @@ impl Interp<'_> {
                 let num = self.to_num(&v);
                 let decimals = pic.split_once('.').map_or(0, |(_, f)| f.chars().filter(|c| matches!(c, '9' | 'z' | 'Z')).count()).min(20);
                 let grouped = pic.contains(',');
-                let mut text = format!("{:.decimals$}", num.abs());
+                let mut text = fixed(num.abs(), decimals);
                 if grouped {
                     let (int, frac) = text.split_once('.').map_or((text.as_str(), ""), |(a, b)| (a, b));
                     let mut g = String::new();
diff --git a/crates/js/src/tests.rs b/crates/js/src/tests.rs
index 55fa45760..4fe5fd290 100644
--- a/crates/js/src/tests.rs
+++ b/crates/js/src/tests.rs
@@ -636,6 +636,19 @@ mod formcalc {
         assert_eq!(calc("; a comment\n// another\nSum(1,\n 2,\n 3)"), "6");
     }
 
+    #[test]
+    fn str_and_format_round_exact_ties_away_from_zero() {
+        assert_eq!(calc("Str(2.5, 3, 0)"), "  3");
+        assert_eq!(calc("Str(0.5, 3, 0)"), "  1");
+        assert_eq!(calc("Str(-2.5, 4, 0)"), "  -3");
+        assert_eq!(calc("Str(1.125, 6, 2)"), "  1.13");
+        assert_eq!(calc(r#"Format("9", 2.5)"#), "3");
+        assert_eq!(calc(r#"Format("9.99", 0.125)"#), "0.13");
+        assert_eq!(calc(r#"Format("9.9", 0.25)"#), "0.3");
+        assert_eq!(calc(r#"Format("9.9", -0.25)"#), "-0.3");
+        assert_eq!(calc(r#"Format("9.99", 2.344)"#), "2.34");
+    }
+
     #[test]
     fn built_in_functions_cover_the_common_set() {
         assert_eq!(calc("Abs(-2.5)"), "2.5");