Add an autogeneration header to pip-compile (#145)

Closes https://github.com/astral-sh/puffin/issues/132.

Cargo.lock

@@ -2136,6 +2136,7 @@ version = "0.0.1"
 dependencies = [
  "anyhow",
  "bitflags 2.4.1",
+ "colored",
  "futures",
  "once_cell",
  "pep440_rs 0.3.12",

crates/puffin-cli/src/commands/pip_compile.rs

@@ -1,3 +1,4 @@
+use std::env;
 use std::fmt::Write;
 use std::io::{stdout, BufWriter};
 use std::path::Path;
@@ -19,6 +20,8 @@ use crate::commands::{elapsed, ExitStatus};
 use crate::printer::Printer;
 use crate::requirements::RequirementsSource;
 
+const VERSION: &str = env!("CARGO_PKG_VERSION");
+
 /// Resolve a set of requirements into a set of pinned versions.
 pub(crate) async fn pip_compile(
     requirements: &[RequirementsSource],
@@ -91,11 +94,24 @@ pub(crate) async fn pip_compile(
         .dimmed()
     )?;
 
-    if let Some(output_file) = output_file {
+    let mut writer: Box<dyn std::io::Write> = if let Some(output_file) = output_file {
-        resolution.write_requirement_format(&mut BufWriter::new(File::create(output_file)?))?;
+        Box::new(BufWriter::new(File::create(output_file)?))
     } else {
-        resolution.write_requirement_format(&mut stdout().lock())?;
+        Box::new(stdout())
     };
 
+    writeln!(
+        writer,
+        "{}",
+        format!("# This file was autogenerated by Puffin v{VERSION} via the following command:")
+            .green()
+    )?;
+    writeln!(
+        writer,
+        "{}",
+        format!("#    {}", env::args().join(" ")).green()
+    )?;
+    writeln!(writer, "{resolution}")?;
+
     Ok(ExitStatus::Success)
 }

crates/puffin-resolver/Cargo.toml

@@ -21,6 +21,7 @@ wheel-filename = { path = "../wheel-filename" }
 
 anyhow = { workspace = true }
 bitflags = { workspace = true }
+colored = { workspace = true }
 futures = { workspace = true }
 once_cell = { workspace = true }
 thiserror = { workspace = true }

crates/puffin-resolver/src/resolution.rs

@@ -1,6 +1,4 @@
 use std::collections::BTreeMap;
-use std::io;
-use std::io::Write;
 
 use pep440_rs::Version;
 use puffin_client::File;
@@ -34,16 +32,9 @@ impl Resolution {
     pub fn is_empty(&self) -> bool {
         self.0.is_empty()
     }
-
-    /// Write the resolution in the `{name}=={version}` format of requirements.txt that pip uses.
-    pub fn write_requirement_format(&self, writer: &mut impl Write) -> io::Result<()> {
-        for (name, package) in self.iter() {
-            writeln!(writer, "{}=={}", name, package.version())?;
-        }
-        Ok(())
-    }
 }
 
+/// Write the resolution in the `{name}=={version}` format of requirements.txt that pip uses.
 impl std::fmt::Display for Resolution {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut first = true;