Merge PR #2992

# Conflicts:
#	docs/function-parity.md

crates/functions/src/text.rs

@@ -281,7 +281,11 @@ fn unichar(a: &[Arg], _c: &mut dyn Ctx) -> R<Value> {
     if !(1.0..=1_114_111.0).contains(&n) {
         return Err(CellError::Value);
     }
-    match char::from_u32(n as u32) {
+    let cp = n as u32;
+    if (0xFDD0..=0xFDEF).contains(&cp) || cp & 0xFFFE == 0xFFFE {
+        return Err(CellError::NA);
+    }
+    match char::from_u32(cp) {
         Some(c) => text_val(c.to_string()),
         None => Err(CellError::NA),
     }
@@ -1181,8 +1185,15 @@ mod tests {
         close(ev("CODE", vec![t("€")]), 128.0);
         is_err(ev("CODE", vec![t("")]), CellError::Value);
         is_text(ev("UNICHAR", vec![n(9731.0)]), "☃");
+        for cp in [0xFDD0, 0xFDEF, 0xFFFE, 0xFFFF, 0x1FFFE, 0x1FFFF, 0x10FFFE, 0x10FFFF] {
+            is_err(ev("UNICHAR", vec![n(f64::from(cp))]), CellError::NA);
+        }
+        for (cp, expected) in [(0xFDCF, "\u{FDCF}"), (0xFDF0, "\u{FDF0}"), (0xFFFD, "\u{FFFD}"), (0x1FFFD, "\u{1FFFD}")] {
+            is_text(ev("UNICHAR", vec![n(f64::from(cp))]), expected);
+        }
         close(ev("UNICODE", vec![t("☃")]), 9731.0);
         is_err(ev("UNICHAR", vec![n(0.0)]), CellError::Value);
+        is_err(ev("UNICHAR", vec![n(1_114_112.0)]), CellError::Value);
         is_err(ev("UNICHAR", vec![n(55296.0)]), CellError::NA);
     }
 

docs/function-parity.md

@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (BITLSHIFT and BITRSHIFT return zero for zero operands with shifts beyond 53 bits, as observed in Excel; earlier: base-conversion places are validated for negative inputs and reject Boolean arguments, as observed in Excel; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; IMSQRT reproduces Excel's stray real part for negative reals) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (UNICHAR returns `#N/A` for Unicode noncharacters, as observed in Excel; earlier: BITLSHIFT and BITRSHIFT return zero for zero operands with shifts beyond 53 bits, as observed in Excel; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; IMSQRT reproduces Excel's stray real part for negative reals) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Excel's worksheet functions, category by category, against GridCraft's function library. Part of
 [target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
@@ -127,6 +127,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 | 2026-10-31 | minor | BIN2*, HEX2* and OCT2* reject surrounding spaces and tabs in source strings with `#NUM!`, matching Excel; plain unpadded values remain valid |
 | 2026-10-31 | minor | DEC2BIN, DEC2HEX and DEC2OCT validate `places` before returning negative two's-complement output, and Boolean places return `#VALUE!`, matching Excel |
 | 2026-10-31 | minor | BITLSHIFT and BITRSHIFT return `0` for zero operands shifted beyond 53 bits in either direction; nonzero operands retain the `#NUM!` limit, matching Excel |
+| 2026-10-31 | minor | UNICHAR returns `#N/A` for U+FDD0–U+FDEF and U+FFFE/U+FFFF on every plane; adjacent valid characters and existing invalid-range/surrogate errors remain unchanged, matching Excel |
 | 2026-10-27 | minor | ECMA.CEILING added to the functions that are in our library but not on Microsoft's list (with USDOLLAR), so the counts don't change |
 | 2026-10-26 | minor | IMSQRT uses Excel's polar route with its cosine reduction, so `IMSQRT("-4")` is `1.22514845490862E-16+2i` as in Excel (exact `2i` before); the rows list the IM* differences still open |
 | 2026-10-25 | minor | LAMBDA row: a LAMBDA that calls itself more than 140 times, and a formula nested past the depth limit, give `#NUM!` (#1809; nesting gave `#CALC!` before). `=Foo(1)` where the defined name Foo holds `#N/A` gives `#N/A`, not `#NAME?` |