Warn when the build cache is inside the source directory

crates/uv/src/commands/build_frontend.rs

@@ -39,6 +39,7 @@ use uv_requirements::RequirementsSource;
 use uv_resolver::{ExcludeNewer, FlatIndex};
 use uv_settings::PythonInstallMirrors;
 use uv_types::{AnyErrorBuild, BuildContext, BuildStack, HashStrategy, SourceTreeEditablePolicy};
+use uv_warnings::warn_user;
 use uv_workspace::pyproject::ExtraBuildDependencies;
 use uv_workspace::{DiscoveryOptions, Workspace, WorkspaceCache, WorkspaceError};
 
@@ -372,16 +373,17 @@ async fn build_impl(
     };
 
     // Build backends can include arbitrary files from the source directory in the distribution.
-    // Reject an active cache within the source to avoid including cache contents in the build.
+    // Warn if the active cache is within the source since cache contents may be included in the
+    // build.
     for source in &packages {
         if let Source::Directory(source_dir) = &source.source
             && is_path_within(cache.root(), source_dir)
         {
-            return Err(anyhow::anyhow!(
-                "The cache directory `{}` is inside the build source directory `{}`",
+            warn_user!(
+                "The cache directory `{}` is inside the build source directory `{}` and may be included in distributions",
                 cache.root().user_display(),
                 source_dir.user_display()
-            ));
+            );
         }
     }
 

crates/uv/tests/build/cache.rs

@@ -7,10 +7,10 @@ use std::process::Command;
 use uv_fs::create_symlink;
 use uv_test::{get_bin, uv_snapshot};
 
-/// When the active cache directory is inside an explicit build source, we should error before
-/// invoking the build backend or creating the output directory.
+/// When the active cache directory is inside an explicit build source, we should warn and continue
+/// the build.
 #[test]
-fn build_rejects_cache_inside_source() -> Result<()> {
+fn build_warns_cache_inside_source() -> Result<()> {
     let mut context = uv_test::test_context!("3.12");
     let project = context.temp_dir.child("project");
 
@@ -31,24 +31,28 @@ fn build_rejects_cache_inside_source() -> Result<()> {
     context.cache_dir = project.child(".uv-cache");
 
     uv_snapshot!(context.filters(), context.build().arg("--sdist").arg("project"), @"
-    success: false
-    exit_code: 2
+    success: true
+    exit_code: 0
     ----- stdout -----
 
     ----- stderr -----
-    error: The cache directory `project/.uv-cache` is inside the build source directory `project`
+    warning: The cache directory `project/.uv-cache` is inside the build source directory `project` and may be included in distributions
+    Building source distribution (uv build backend)...
+    Successfully built project/dist/project-0.1.0.tar.gz
     ");
 
-    project.child("dist").assert(predicate::path::missing());
+    project
+        .child("dist/project-0.1.0.tar.gz")
+        .assert(predicate::path::is_file());
 
     Ok(())
 }
 
-/// When the canonical cache directory is inside an explicit build source, we should error even if
+/// When the canonical cache directory is inside an explicit build source, we should warn even if
 /// the configured cache path itself is outside the source.
 #[test]
 #[cfg(unix)]
-fn build_rejects_symlinked_cache_inside_source() -> Result<()> {
+fn build_warns_symlinked_cache_inside_source() -> Result<()> {
     let context = uv_test::test_context!("3.12");
     let project = context.temp_dir.child("project");
 
@@ -82,15 +86,19 @@ fn build_rejects_symlinked_cache_inside_source() -> Result<()> {
     command.current_dir(context.temp_dir.path());
 
     uv_snapshot!(context.filters(), command, @"
-    success: false
-    exit_code: 2
+    success: true
+    exit_code: 0
     ----- stdout -----
 
     ----- stderr -----
-    error: The cache directory `cache-link` is inside the build source directory `project`
+    warning: The cache directory `cache-link` is inside the build source directory `project` and may be included in distributions
+    Building source distribution (uv build backend)...
+    Successfully built project/dist/project-0.1.0.tar.gz
     ");
 
-    project.child("dist").assert(predicate::path::missing());
+    project
+        .child("dist/project-0.1.0.tar.gz")
+        .assert(predicate::path::is_file());
 
     Ok(())
 }