fold:fix gnu test fold-zero-width.sh (#9274)

---------

Co-authored-by: Sylvestre Ledru <sylvestre@debian.org>

Author: mattsu2020

Cargo.lock

@@ -535,13 +535,15 @@ filetime.workspace = true
 glob.workspace = true
 jiff.workspace = true
 libc.workspace = true
+bytecount.workspace = true
 num-prime.workspace = true
 pretty_assertions = "1.4.0"
 rand.workspace = true
 regex.workspace = true
 sha1 = { workspace = true, features = ["std"] }
 tempfile.workspace = true
 time = { workspace = true, features = ["local-offset"] }
+unicode-width.workspace = true
 unindent = "0.2.3"
 uutests.workspace = true
 uucore = { workspace = true, features = [

Cargo.toml

@@ -19,6 +19,10 @@ const TAB_WIDTH: usize = 8;
 const NL: u8 = b'\n';
 const CR: u8 = b'\r';
 const TAB: u8 = b'\t';
+// Implementation threshold (8 KiB) to prevent unbounded buffer growth during streaming.
+// Chosen as a small, fixed cap: large enough to avoid excessive flushes, but
+// small enough to keep memory bounded when the input has no fold points.
+const STREAMING_FLUSH_THRESHOLD: usize = 8 * 1024;
 
 mod options {
     pub const BYTES: &str = "bytes";
@@ -288,6 +292,10 @@ fn compute_col_count(buffer: &[u8], mode: WidthMode) -> usize {
 }
 
 fn emit_output<W: Write>(ctx: &mut FoldContext<'_, W>) -> UResult<()> {
+    // Emit one folded line:
+    // - with `-s`, cut at the last remembered whitespace when possible
+    // - otherwise, cut at the current buffer end
+    // The remainder (if any) stays in the buffer for the next line.
     let consume = match *ctx.last_space {
         Some(index) => index + 1,
         None => ctx.output.len(),
@@ -309,6 +317,7 @@ fn emit_output<W: Write>(ctx: &mut FoldContext<'_, W>) -> UResult<()> {
     *ctx.col_count = compute_col_count(ctx.output, ctx.mode);
 
     if ctx.spaces {
+        // Rebase the remembered whitespace position into the remaining buffer.
         *ctx.last_space = last_space.and_then(|idx| {
             if idx < consume {
                 None
@@ -322,6 +331,36 @@ fn emit_output<W: Write>(ctx: &mut FoldContext<'_, W>) -> UResult<()> {
     Ok(())
 }
 
+fn maybe_flush_unbroken_output<W: Write>(ctx: &mut FoldContext<'_, W>) -> UResult<()> {
+    // In streaming mode without `-s`, avoid unbounded buffering by periodically
+    // flushing long unbroken segments. With `-s` we must keep the buffer so we
+    // can still break at the last whitespace boundary.
+    if ctx.spaces || ctx.output.len() < STREAMING_FLUSH_THRESHOLD {
+        return Ok(());
+    }
+
+    // Write raw bytes without inserting a newline; folding will continue
+    // based on updated column tracking in the caller.
+    ctx.writer.write_all(ctx.output)?;
+    ctx.output.clear();
+    Ok(())
+}
+
+fn push_byte<W: Write>(ctx: &mut FoldContext<'_, W>, byte: u8) -> UResult<()> {
+    // Append a single byte to the buffer.
+    ctx.output.push(byte);
+    maybe_flush_unbroken_output(ctx)
+}
+
+fn push_bytes<W: Write>(ctx: &mut FoldContext<'_, W>, bytes: &[u8]) -> UResult<()> {
+    // Append a byte slice to the buffer and flush if it grows too large.
+    if bytes.is_empty() {
+        return Ok(());
+    }
+    ctx.output.extend_from_slice(bytes);
+    maybe_flush_unbroken_output(ctx)
+}
+
 fn process_ascii_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) -> UResult<()> {
     let mut idx = 0;
     let len = line.len();
@@ -331,15 +370,15 @@ fn process_ascii_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) -> UR
             NL => {
                 *ctx.last_space = None;
                 emit_output(ctx)?;
-                break;
+                idx += 1;
             }
             CR => {
-                ctx.output.push(CR);
+                push_byte(ctx, CR)?;
                 *ctx.col_count = 0;
                 idx += 1;
             }
             0x08 => {
-                ctx.output.push(0x08);
+                push_byte(ctx, 0x08)?;
                 *ctx.col_count = ctx.col_count.saturating_sub(1);
                 idx += 1;
             }
@@ -358,16 +397,23 @@ fn process_ascii_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) -> UR
                 } else {
                     *ctx.last_space = None;
                 }
-                ctx.output.push(TAB);
+                push_byte(ctx, TAB)?;
                 idx += 1;
             }
             0x00..=0x07 | 0x0B..=0x0C | 0x0E..=0x1F | 0x7F => {
-                ctx.output.push(line[idx]);
+                push_byte(ctx, line[idx])?;
                 if ctx.spaces && line[idx].is_ascii_whitespace() && line[idx] != CR {
                     *ctx.last_space = Some(ctx.output.len() - 1);
                 } else if !ctx.spaces {
                     *ctx.last_space = None;
                 }
+
+                if ctx.mode == WidthMode::Characters {
+                    *ctx.col_count = ctx.col_count.saturating_add(1);
+                    if *ctx.col_count >= ctx.width {
+                        emit_output(ctx)?;
+                    }
+                }
                 idx += 1;
             }
             _ => {
@@ -405,7 +451,7 @@ fn push_ascii_segment<W: Write>(segment: &[u8], ctx: &mut FoldContext<'_, W>) ->
         let take = remaining.len().min(available);
         let base_len = ctx.output.len();
 
-        ctx.output.extend_from_slice(&remaining[..take]);
+        push_bytes(ctx, &remaining[..take])?;
         *ctx.col_count += take;
 
         if ctx.spaces {
@@ -430,16 +476,26 @@ fn process_utf8_line<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> URes
         return process_ascii_line(line.as_bytes(), ctx);
     }
 
+    process_utf8_chars(line, ctx)
+}
+
+fn process_utf8_chars<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> UResult<()> {
     let line_bytes = line.as_bytes();
     let mut iter = line.char_indices().peekable();
 
     while let Some((byte_idx, ch)) = iter.next() {
-        // Include combining characters with the base character
-        while let Some(&(_, next_ch)) = iter.peek() {
-            if unicode_width::UnicodeWidthChar::width(next_ch).unwrap_or(1) == 0 {
-                iter.next();
-            } else {
-                break;
+        // Include combining characters with the base character when we are
+        // measuring by display columns. In character-counting mode every
+        // scalar value must advance the counter to match `chars().count()`
+        // semantics (see `fold_characters_reference` in the tests), so we do
+        // not coalesce zero-width scalars there.
+        if ctx.mode == WidthMode::Columns {
+            while let Some(&(_, next_ch)) = iter.peek() {
+                if unicode_width::UnicodeWidthChar::width(next_ch).unwrap_or(1) == 0 {
+                    iter.next();
+                } else {
+                    break;
+                }
             }
         }
 
@@ -448,23 +504,21 @@ fn process_utf8_line<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> URes
         if ch == '\n' {
             *ctx.last_space = None;
             emit_output(ctx)?;
-            break;
+            continue;
         }
 
         if *ctx.col_count >= ctx.width {
             emit_output(ctx)?;
         }
 
         if ch == '\r' {
-            ctx.output
-                .extend_from_slice(&line_bytes[byte_idx..next_idx]);
+            push_bytes(ctx, &line_bytes[byte_idx..next_idx])?;
             *ctx.col_count = 0;
             continue;
         }
 
         if ch == '\x08' {
-            ctx.output
-                .extend_from_slice(&line_bytes[byte_idx..next_idx]);
+            push_bytes(ctx, &line_bytes[byte_idx..next_idx])?;
             *ctx.col_count = ctx.col_count.saturating_sub(1);
             continue;
         }
@@ -484,8 +538,7 @@ fn process_utf8_line<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> URes
             } else {
                 *ctx.last_space = None;
             }
-            ctx.output
-                .extend_from_slice(&line_bytes[byte_idx..next_idx]);
+            push_bytes(ctx, &line_bytes[byte_idx..next_idx])?;
             continue;
         }
 
@@ -506,8 +559,7 @@ fn process_utf8_line<W: Write>(line: &str, ctx: &mut FoldContext<'_, W>) -> URes
             *ctx.last_space = Some(ctx.output.len());
         }
 
-        ctx.output
-            .extend_from_slice(&line_bytes[byte_idx..next_idx]);
+        push_bytes(ctx, &line_bytes[byte_idx..next_idx])?;
         *ctx.col_count = ctx.col_count.saturating_add(added);
     }
 
@@ -519,7 +571,7 @@ fn process_non_utf8_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) ->
         if byte == NL {
             *ctx.last_space = None;
             emit_output(ctx)?;
-            break;
+            continue;
         }
 
         if *ctx.col_count >= ctx.width {
@@ -539,7 +591,7 @@ fn process_non_utf8_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) ->
                 } else {
                     None
                 };
-                ctx.output.push(byte);
+                push_byte(ctx, byte)?;
                 continue;
             }
             0x08 => *ctx.col_count = ctx.col_count.saturating_sub(1),
@@ -550,7 +602,46 @@ fn process_non_utf8_line<W: Write>(line: &[u8], ctx: &mut FoldContext<'_, W>) ->
             _ => *ctx.col_count = ctx.col_count.saturating_add(1),
         }
 
-        ctx.output.push(byte);
+        push_byte(ctx, byte)?;
+    }
+
+    Ok(())
+}
+
+/// Process buffered bytes, emitting output for valid UTF-8 prefixes and
+/// deferring incomplete sequences until more input arrives.
+///
+/// If the buffer contains invalid UTF-8, it is handled in non-UTF-8 mode and
+/// the buffer is fully consumed.
+fn process_pending_chunk<W: Write>(
+    pending: &mut Vec<u8>,
+    ctx: &mut FoldContext<'_, W>,
+) -> UResult<()> {
+    while !pending.is_empty() {
+        match std::str::from_utf8(pending) {
+            Ok(valid) => {
+                process_utf8_line(valid, ctx)?;
+                pending.clear();
+                break;
+            }
+            Err(err) => {
+                if err.error_len().is_some() {
+                    let res = process_non_utf8_line(pending, ctx);
+                    pending.clear();
+                    res?;
+                    break;
+                }
+
+                let valid_up_to = err.valid_up_to();
+                if valid_up_to == 0 {
+                    break;
+                }
+
+                let valid = std::str::from_utf8(&pending[..valid_up_to]).expect("valid prefix");
+                process_utf8_line(valid, ctx)?;
+                pending.drain(..valid_up_to);
+            }
+        }
     }
 
     Ok(())
@@ -572,20 +663,12 @@ fn fold_file<T: Read, W: Write>(
     mode: WidthMode,
     writer: &mut W,
 ) -> UResult<()> {
-    let mut line = Vec::new();
     let mut output = Vec::new();
     let mut col_count = 0;
     let mut last_space = None;
+    let mut pending = Vec::with_capacity(8 * 1024);
 
-    loop {
-        if file
-            .read_until(NL, &mut line)
-            .map_err_context(|| translate!("fold-error-readline"))?
-            == 0
-        {
-            break;
-        }
-
+    {
         let mut ctx = FoldContext {
             spaces,
             width,
@@ -596,17 +679,32 @@ fn fold_file<T: Read, W: Write>(
             last_space: &mut last_space,
         };
 
-        match std::str::from_utf8(&line) {
-            Ok(s) => process_utf8_line(s, &mut ctx)?,
-            Err(_) => process_non_utf8_line(&line, &mut ctx)?,
+        loop {
+            let buffer = file
+                .fill_buf()
+                .map_err_context(|| translate!("fold-error-readline"))?;
+            if buffer.is_empty() {
+                break;
+            }
+            pending.extend_from_slice(buffer);
+            let consumed = buffer.len();
+            file.consume(consumed);
+
+            process_pending_chunk(&mut pending, &mut ctx)?;
         }
 
-        line.clear();
-    }
+        if !pending.is_empty() {
+            match std::str::from_utf8(&pending) {
+                Ok(s) => process_utf8_line(s, &mut ctx)?,
+                Err(_) => process_non_utf8_line(&pending, &mut ctx)?,
+            }
+            pending.clear();
+        }
 
-    if !output.is_empty() {
-        writer.write_all(&output)?;
-        output.clear();
+        if !ctx.output.is_empty() {
+            ctx.writer.write_all(ctx.output)?;
+            ctx.output.clear();
+        }
     }
 
     Ok(())