libherokubuildpack: Fix colour resetting for the log_* macros

CHANGELOG.md

@@ -9,13 +9,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- `libherokubuildpack`:
+  - Fixed `log_header`, `log_error` and `log_warning` to correctly reset the ANSI colour styles at the end of each line. ([#890](https://github.com/heroku/libcnb.rs/pull/890))
 
 ## [0.26.0] - 2024-11-18
 
 ### Changed
 
 - `libherokubuildpack`:
-  - Removed `buildpack_output` module. This functionality from ([#721](https://github.com/heroku/libcnb.rs/pull/721)) was experimental. The API was not stable and it is being removed. A similar API is available at [bullet_stream](https://crates.io/crates/bullet_stream). ([#852](https://github.com/heroku/libcnb.rs/pull/852)
+  - Removed `buildpack_output` module. This functionality from ([#721](https://github.com/heroku/libcnb.rs/pull/721)) was experimental. The API was not stable and it is being removed. A similar API is available at [bullet_stream](https://crates.io/crates/bullet_stream). ([#852](https://github.com/heroku/libcnb.rs/pull/852))
 
 ## [0.25.0] - 2024-10-23
 

libherokubuildpack/src/log.rs

@@ -1,4 +1,4 @@
-use std::io::Write;
+use std::io::{self, Write};
 use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
 
 /// # Panics
@@ -10,16 +10,14 @@ use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
 #[allow(clippy::unwrap_used)]
 pub fn log_error(header: impl AsRef<str>, body: impl AsRef<str>) {
     let mut stream = StandardStream::stderr(ColorChoice::Always);
-    stream
-        .set_color(ColorSpec::new().set_fg(Some(Color::Red)).set_bold(true))
-        .unwrap();
-    writeln!(&mut stream, "\n[Error: {}]", header.as_ref()).unwrap();
-    stream.reset().unwrap();
+    write_styled_message(
+        &mut stream,
+        format!("\n[Error: {}]", header.as_ref()),
+        ColorSpec::new().set_fg(Some(Color::Red)).set_bold(true),
+    )
+    .unwrap();
 
-    stream
-        .set_color(ColorSpec::new().set_fg(Some(Color::Red)))
-        .unwrap();
-    writeln!(&mut stream, "{}", body.as_ref()).unwrap();
+    write_styled_message(&mut stream, body, ColorSpec::new().set_fg(Some(Color::Red))).unwrap();
     stream.flush().unwrap();
 }
 
@@ -32,16 +30,19 @@ pub fn log_error(header: impl AsRef<str>, body: impl AsRef<str>) {
 #[allow(clippy::unwrap_used)]
 pub fn log_warning(header: impl AsRef<str>, body: impl AsRef<str>) {
     let mut stream = StandardStream::stderr(ColorChoice::Always);
-    stream
-        .set_color(ColorSpec::new().set_fg(Some(Color::Yellow)).set_bold(true))
-        .unwrap();
-    writeln!(&mut stream, "\n[Warning: {}]", header.as_ref()).unwrap();
-    stream.reset().unwrap();
+    write_styled_message(
+        &mut stream,
+        format!("\n[Warning: {}]", header.as_ref()),
+        ColorSpec::new().set_fg(Some(Color::Yellow)).set_bold(true),
+    )
+    .unwrap();
 
-    stream
-        .set_color(ColorSpec::new().set_fg(Some(Color::Yellow)))
-        .unwrap();
-    writeln!(&mut stream, "{}", body.as_ref()).unwrap();
+    write_styled_message(
+        &mut stream,
+        body,
+        ColorSpec::new().set_fg(Some(Color::Yellow)),
+    )
+    .unwrap();
     stream.flush().unwrap();
 }
 
@@ -54,11 +55,12 @@ pub fn log_warning(header: impl AsRef<str>, body: impl AsRef<str>) {
 #[allow(clippy::unwrap_used)]
 pub fn log_header(title: impl AsRef<str>) {
     let mut stream = StandardStream::stdout(ColorChoice::Always);
-    stream
-        .set_color(ColorSpec::new().set_fg(Some(Color::Magenta)).set_bold(true))
-        .unwrap();
-    writeln!(&mut stream, "\n[{}]", title.as_ref()).unwrap();
-    stream.reset().unwrap();
+    write_styled_message(
+        &mut stream,
+        format!("\n[{}]", title.as_ref()),
+        ColorSpec::new().set_fg(Some(Color::Magenta)).set_bold(true),
+    )
+    .unwrap();
     stream.flush().unwrap();
 }
 
@@ -72,3 +74,22 @@ pub fn log_info(message: impl AsRef<str>) {
     println!("{}", message.as_ref());
     std::io::stdout().flush().unwrap();
 }
+
+// Styles each line of text separately, so that when buildpack output is streamed to the
+// user (and prefixes like `remote:` added) the line colour doesn't leak into the prefixes.
+fn write_styled_message(
+    stream: &mut StandardStream,
+    message: impl AsRef<str>,
+    spec: &ColorSpec,
+) -> io::Result<()> {
+    // Using `.split('\n')` rather than `.lines()` since the latter eats trailing newlines in
+    // the passed message, which would (a) prevent the caller from being able to add spacing at
+    // the end of their message and (b) differ from the `println!` / `writeln!` behaviour.
+    for line in message.as_ref().split('\n') {
+        stream.set_color(spec)?;
+        write!(stream, "{line}")?;
+        stream.reset()?;
+        writeln!(stream)?;
+    }
+    Ok(())
+}