From 8fad4393fec11d2717eeb262d0a3e247adf36e01 Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@cs.stanford.edu>
Date: Sun, 24 Aug 2025 15:17:47 -0700
Subject: [PATCH] rust: Make .display_plain() for f64 support alternate decimal
 points.

---
 rust/pspp/src/format/display/mod.rs | 62 ++++++++++++++++++++++-------
 rust/pspp/src/sys/raw/records.rs    |  6 +--
 rust/pspp/src/sys/write.rs          |  4 +-
 3 files changed, 53 insertions(+), 19 deletions(-)

diff --git a/rust/pspp/src/format/display/mod.rs b/rust/pspp/src/format/display/mod.rs
index 6f65cee10e..79a4c106f1 100644
--- a/rust/pspp/src/format/display/mod.rs
+++ b/rust/pspp/src/format/display/mod.rs
@@ -56,29 +56,63 @@ pub struct DisplayDatum<'b, B> {
 mod test;
 
 pub trait DisplayPlain {
-    fn display_plain(&self) -> impl Display;
+    fn display_plain(&self) -> DisplayPlainF64;
 }
 
 impl DisplayPlain for f64 {
-    fn display_plain(&self) -> impl Display {
-        DisplayPlainF64(*self)
+    fn display_plain(&self) -> DisplayPlainF64 {
+        DisplayPlainF64 {
+            value: *self,
+            decimal: '.',
+        }
     }
 }
 
-pub struct DisplayPlainF64(pub f64);
+pub struct DisplayPlainF64 {
+    pub value: f64,
+    pub decimal: char,
+}
+
+impl DisplayPlainF64 {
+    pub fn with_decimal(self, decimal: char) -> Self {
+        Self { decimal, ..self }
+    }
+}
 
 impl Display for DisplayPlainF64 {
     fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
-        if self.0.abs() < 0.0005 || self.0.abs() > 1e15 {
-            // Print self.0s that would otherwise have lots of leading or
-            // trailing zeros in scientific notation with full precision.
-            write!(f, "{:.e}", self.0)
-        } else if self.0 == self.0.trunc() {
-            // Print integers without decimal places.
-            write!(f, "{:.0}", self.0)
-        } else {
-            // Print other numbers with full precision.
-            write!(f, "{:.}", self.0)
+        struct Inner(f64);
+
+        impl Display for Inner {
+            fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
+                let value = self.0;
+                if (value.abs() < 0.0005 && value != 0.0) || value.abs() > 1e15 {
+                    // Print 0s that would otherwise have lots of leading or
+                    // trailing zeros in scientific notation with full precision.
+                    write!(f, "{value:.e}")
+                } else if value == value.trunc() {
+                    // Print integers without decimal places.
+                    write!(f, "{value:.0}")
+                } else {
+                    // Print other numbers with full precision.
+                    write!(f, "{value:.}")
+                }
+            }
+        }
+
+        match self.decimal {
+            '.' => write!(f, "{}", Inner(self.value)),
+            _ => {
+                let mut tmp = SmallString::<[u8; 64]>::new();
+                write!(&mut tmp, "{}", Inner(self.value)).unwrap();
+                if let Some(position) = tmp.find('.') {
+                    f.write_str(&tmp[..position])?;
+                    f.write_char(self.decimal)?;
+                    f.write_str(&tmp[position + 1..])
+                } else {
+                    f.write_str(&tmp)
+                }
+            }
         }
     }
 }
diff --git a/rust/pspp/src/sys/raw/records.rs b/rust/pspp/src/sys/raw/records.rs
index 5269d26d98..b54f8d6da3 100644
--- a/rust/pspp/src/sys/raw/records.rs
+++ b/rust/pspp/src/sys/raw/records.rs
@@ -15,7 +15,7 @@ use crate::{
     data::{ByteStrArray, ByteString, Datum},
     dictionary::CategoryLabels,
     endian::FromBytes,
-    format::{DisplayPlainF64, Format, Type},
+    format::{DisplayPlain, Format, Type},
     identifier::{Error as IdError, Identifier},
     sys::{
         raw::{
@@ -2672,8 +2672,8 @@ pub enum ZTrailerError {
     /// ZLIB trailer bias {actual} is not {} as expected from file header bias.
     #[
         error(
-        "Bias {actual} is not {} as expected from file header.",
-        DisplayPlainF64(*expected)
+            "Bias {actual} is not {} as expected from file header.",
+            expected.display_plain()
     )]
     WrongZlibTrailerBias {
         /// ZLIB trailer bias read from file.
diff --git a/rust/pspp/src/sys/write.rs b/rust/pspp/src/sys/write.rs
index 8b12ea268e..d67b73575b 100644
--- a/rust/pspp/src/sys/write.rs
+++ b/rust/pspp/src/sys/write.rs
@@ -35,7 +35,7 @@ use smallvec::SmallVec;
 use crate::{
     data::{Datum, RawString},
     dictionary::{CategoryLabels, Dictionary, MultipleResponseType},
-    format::{DisplayPlainF64, Format},
+    format::{DisplayPlain, Format},
     identifier::Identifier,
     output::spv::Zeros,
     sys::{
@@ -536,7 +536,7 @@ where
 
                     let mut value = match datum {
                         Datum::Number(Some(number)) => {
-                            DisplayPlainF64(*number).to_string().into_bytes()
+                            number.display_plain().to_string().into_bytes()
                         }
                         Datum::Number(None) => vec![b'.'],
                         Datum::String(raw_string) => raw_string.0.clone(),
-- 
2.30.2