Revert removing log and changes to on_error

We still want the `log` feature to exist until all buildpacks have
transitioned over to `build_output`, since:
1. It will ease the transition for repositories where there are
   multiple buildpacks, since each buildpack can be migrated
   to `build_output` individually, rather than needing to do
   all of them at once.
2. It means any buildpacks that cannot switch to `build_output`
   right away, can still stay up to date with other libcnb changes.

The change to `on_error` has also been reverted, since:
1. It's a change that's standalone from introducing the
   `build_output` module (ie: lets first introduce a new thing,
   then afterwards handle migrating things to use it)
2. It's otherwise yet another thing we need to review in this
   already very-long lived PR, and it would be best to avoid
   further delays. (I can see at least one issue with the change
   that would need fixing, and I haven't even reviewed it fully
  yet.)

CHANGELOG.md

@@ -9,11 +9,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-### Changed
-
-- `libherokubuildpack`:
-  - Removed the `log` module in favor of `buildpack_output`. ([#721](https://github.com/heroku/libcnb.rs/pull/721))
-
 ### Added
 
 - `libherokubuildpack`:

libherokubuildpack/Cargo.toml

@@ -18,10 +18,11 @@ all-features = true
 workspace = true
 
 [features]
-default = ["command", "download", "digest", "tar", "toml", "fs", "write", "buildpack_output"]
+default = ["command", "download", "digest", "error", "log", "tar", "toml", "fs", "write", "buildpack_output"]
 download = ["dep:ureq", "dep:thiserror"]
 digest = ["dep:sha2"]
-error = ["buildpack_output", "dep:libcnb"]
+error = ["log", "dep:libcnb"]
+log = ["dep:termcolor"]
 tar = ["dep:tar", "dep:flate2"]
 toml = ["dep:toml"]
 fs = ["dep:pathdiff"]
@@ -41,6 +42,7 @@ libcnb = { workspace = true, optional = true }
 pathdiff = { version = "0.2.1", optional = true }
 sha2 = { version = "0.10.8", optional = true }
 tar = { version = "0.4.40", default-features = false, optional = true }
+termcolor = { version = "1.4.1", optional = true }
 thiserror = { version = "1.0.57", optional = true }
 toml = { workspace = true, optional = true }
 ureq = { version = "2.9.5", default-features = false, features = ["tls"], optional = true }

libherokubuildpack/src/error.rs

@@ -1,11 +1,11 @@
-use crate::buildpack_output::BuildpackOutput;
+use crate::log::log_error;
 use std::fmt::Debug;
 
 /// Handles a given [`libcnb::Error`] in a consistent style.
 ///
 /// This function is intended to be used inside [`libcnb::Buildpack::on_error`].
 ///
-/// It outputs generic libcnb errors in a consistent style using [`BuildpackOutput`] from this
+/// It outputs generic libcnb errors in a consistent style using the [logging functions](log_error) from this
 /// crate. Buildpack specific errors are handled by the passed custom handler.
 ///
 /// # Example:
@@ -14,7 +14,7 @@ use std::fmt::Debug;
 /// use libcnb::Buildpack;
 /// use libcnb::detect::{DetectContext, DetectResult};
 /// use libcnb::generic::{GenericMetadata, GenericPlatform};
-/// use libherokubuildpack::buildpack_output::BuildpackOutput;
+/// use libherokubuildpack::log::log_error;
 /// use libherokubuildpack::error::on_error;
 ///
 /// #[derive(Debug)]
@@ -24,13 +24,12 @@ use std::fmt::Debug;
 /// }
 ///
 /// fn on_foo_buildpack_error(e: FooBuildpackError) {
-///     let output = BuildpackOutput::new(std::io::stdout()).start_silent();
 ///     match e {
 ///         FooBuildpackError::InvalidFooDescriptorToml => {
-///             output.error("Invalid foo.toml\n\nYour app's foo.toml is invalid!");
+///             log_error("Invalid foo.toml", "Your app's foo.toml is invalid!");
 ///         }
 ///         FooBuildpackError::CannotExecuteFooBuildTool(inner) => {
-///             output.error(format!("Couldn't execute foo build tool\n\nYour app's foo.toml is invalid!\n\nCause: {}", &inner));
+///             log_error("Couldn't execute foo build tool", format!("Cause: {}", &inner));
 ///         }
 ///     }
 /// }
@@ -64,9 +63,7 @@ where
     match error {
         libcnb::Error::BuildpackError(buildpack_error) => f(buildpack_error),
         libcnb_error => {
-            BuildpackOutput::new(std::io::stdout())
-                .start_silent()
-                .error(format!("Internal Buildpack Error\n\n{libcnb_error}"));
+            log_error("Internal Buildpack Error", libcnb_error.to_string());
         }
     }
 }

libherokubuildpack/src/lib.rs

@@ -12,6 +12,8 @@ pub mod download;
 pub mod error;
 #[cfg(feature = "fs")]
 pub mod fs;
+#[cfg(feature = "log")]
+pub mod log;
 #[cfg(feature = "tar")]
 pub mod tar;
 #[cfg(feature = "toml")]

libherokubuildpack/src/log.rs

@@ -0,0 +1,74 @@
+use std::io::Write;
+use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
+
+/// # Panics
+///
+/// Will panic if there was a problem setting the color settings, or all bytes could
+/// not be written due to either I/O errors or EOF being reached.
+// TODO: Replace `.unwrap()` usages with `.expect()` to give a clearer error message:
+// https://github.com/heroku/libcnb.rs/issues/712
+#[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();
+
+    stream
+        .set_color(ColorSpec::new().set_fg(Some(Color::Red)))
+        .unwrap();
+    writeln!(&mut stream, "{}", body.as_ref()).unwrap();
+    stream.flush().unwrap();
+}
+
+/// # Panics
+///
+/// Will panic if there was a problem setting the color settings, or all bytes could
+/// not be written due to either I/O errors or EOF being reached.
+// TODO: Replace `.unwrap()` usages with `.expect()` to give a clearer error message:
+// https://github.com/heroku/libcnb.rs/issues/712
+#[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();
+
+    stream
+        .set_color(ColorSpec::new().set_fg(Some(Color::Yellow)))
+        .unwrap();
+    writeln!(&mut stream, "{}", body.as_ref()).unwrap();
+    stream.flush().unwrap();
+}
+
+/// # Panics
+///
+/// Will panic if there was a problem setting the color settings, or all bytes could
+/// not be written due to either I/O errors or EOF being reached.
+// TODO: Replace `.unwrap()` usages with `.expect()` to give a clearer error message:
+// https://github.com/heroku/libcnb.rs/issues/712
+#[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();
+    stream.flush().unwrap();
+}
+
+/// # Panics
+///
+/// Will panic if all bytes could not be written due to I/O errors or EOF being reached.
+// TODO: Replace `.unwrap()` usages with `.expect()` to give a clearer error message:
+// https://github.com/heroku/libcnb.rs/issues/712
+#[allow(clippy::unwrap_used)]
+pub fn log_info(message: impl AsRef<str>) {
+    println!("{}", message.as_ref());
+    std::io::stdout().flush().unwrap();
+}