Add dependents ("via ..." comments) in export command

crates/uv-cli/src/lib.rs

@@ -3851,6 +3851,13 @@ pub struct ExportArgs {
     #[arg(long, conflicts_with_all = ["only_group", "only_dev"])]
     pub all_groups: bool,
 
+    /// Exclude comment annotations indicating the source of each package.
+    #[arg(long, overrides_with("annotate"))]
+    pub no_annotate: bool,
+
+    #[arg(long, overrides_with("no_annotate"), hide = true)]
+    pub annotate: bool,
+
     /// Exclude the comment header at the top of the generated output file.
     #[arg(long, overrides_with("header"))]
     pub no_header: bool,

crates/uv-resolver/src/lock/requirements_txt.rs

@@ -5,6 +5,7 @@ use std::fmt::Formatter;
 use std::path::{Component, Path, PathBuf};
 
 use either::Either;
+use owo_colors::OwoColorize;
 use petgraph::graph::NodeIndex;
 use petgraph::prelude::EdgeRef;
 use petgraph::visit::IntoNodeReferences;
@@ -41,6 +42,7 @@ impl<'lock> RequirementsTxtExport<'lock> {
         prune: &[PackageName],
         extras: &ExtrasSpecification,
         dev: &DependencyGroupsWithDefaults,
+        annotate: bool,
         editable: EditableMode,
         hashes: bool,
         install_options: &'lock InstallOptions,
@@ -312,6 +314,21 @@ impl<'lock> RequirementsTxtExport<'lock> {
             .map(|(index, package)| Requirement {
                 package,
                 marker: reachability.remove(&index).unwrap_or_default(),
+                dependents: if annotate {
+                    let mut dependents = graph
+                        .edges_directed(index, Direction::Incoming)
+                        .map(|edge| &graph[edge.source()])
+                        .filter_map(|node| match node {
+                            Node::Package(package) => Some(*package),
+                            Node::Root => None,
+                        })
+                        .collect::<Vec<_>>();
+                    dependents.sort_unstable_by_key(|package| package.name());
+                    dependents.dedup_by_key(|package| package.name());
+                    dependents
+                } else {
+                    Vec::new()
+                },
             })
             .filter(|requirement| !requirement.marker.is_false())
             .collect::<Vec<_>>();
@@ -496,7 +513,12 @@ fn conflict_marker_reachability<'lock>(
 impl std::fmt::Display for RequirementsTxtExport<'_> {
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         // Write out each package.
-        for Requirement { package, marker } in &self.nodes {
+        for Requirement {
+            package,
+            marker,
+            dependents,
+        } in &self.nodes
+        {
             match &package.id.source {
                 Source::Registry(_) => {
                     let version = package
@@ -586,6 +608,20 @@ impl std::fmt::Display for RequirementsTxtExport<'_> {
             }
 
             writeln!(f)?;
+
+            // Add "via ..." comments for all dependents.
+            match dependents.as_slice() {
+                [] => {}
+                [dependent] => {
+                    writeln!(f, "{}", format!("    # via {}", dependent.id.name).green())?;
+                }
+                _ => {
+                    writeln!(f, "{}", "    # via".green())?;
+                    for &dependent in dependents {
+                        writeln!(f, "{}", format!("    #   {}", dependent.id.name).green())?;
+                    }
+                }
+            }
         }
 
         Ok(())
@@ -637,6 +673,7 @@ impl Reachable<MarkerTree> for Edge<'_> {
 struct Requirement<'lock> {
     package: &'lock Package,
     marker: MarkerTree,
+    dependents: Vec<&'lock Package>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]

crates/uv/src/commands/project/export.rs

@@ -63,6 +63,7 @@ pub(crate) async fn export(
     editable: EditableMode,
     locked: bool,
     frozen: bool,
+    include_annotations: bool,
     include_header: bool,
     script: Option<Pep723Script>,
     python: Option<String>,
@@ -259,6 +260,7 @@ pub(crate) async fn export(
                 &prune,
                 &extras,
                 &dev,
+                include_annotations,
                 editable,
                 hashes,
                 &install_options,

crates/uv/src/lib.rs

@@ -1916,6 +1916,7 @@ async fn run_project(
                 args.editable,
                 args.locked,
                 args.frozen,
+                args.include_annotations,
                 args.include_header,
                 script,
                 args.python,

crates/uv/src/settings.rs

@@ -1523,6 +1523,7 @@ pub(crate) struct ExportSettings {
     pub(crate) output_file: Option<PathBuf>,
     pub(crate) locked: bool,
     pub(crate) frozen: bool,
+    pub(crate) include_annotations: bool,
     pub(crate) include_header: bool,
     pub(crate) script: Option<PathBuf>,
     pub(crate) python: Option<String>,
@@ -1552,6 +1553,8 @@ impl ExportSettings {
             no_default_groups,
             only_group,
             all_groups,
+            annotate,
+            no_annotate,
             header,
             no_header,
             no_editable,
@@ -1604,6 +1607,7 @@ impl ExportSettings {
             output_file,
             locked,
             frozen,
+            include_annotations: flag(annotate, no_annotate).unwrap_or(true),
             include_header: flag(header, no_header).unwrap_or(true),
             script,
             python: python.and_then(Maybe::into_option),