Invalidate cache when --config-settings change (#7139)

## Summary

If `--config-settings` are provided, we cache the built wheels under one
more subdirectory.

We _don't_ invalidate the actual source (i.e., trigger a re-download) or
metadata, though -- those can be reused even when `--config-settings`
change.

Closes https://github.com/astral-sh/uv/issues/7028.

crates/uv-distribution/src/source/mod.rs

@@ -426,6 +426,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
         // freshness, since entries have to be fresher than the revision itself.
         let cache_shard = cache_shard.shard(revision.id());
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // If the cache contains a compatible wheel, return it.
         if let Some(built_wheel) = BuiltWheelMetadata::find_in_cache(tags, &cache_shard) {
             return Ok(built_wheel.with_hashes(revision.into_hashes()));
@@ -519,6 +527,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
             });
         }
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // Otherwise, we either need to build the metadata.
         // If the backend supports `prepare_metadata_for_build_wheel`, use it.
         if let Some(metadata) = self
@@ -671,6 +687,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
         // freshness, since entries have to be fresher than the revision itself.
         let cache_shard = cache_shard.shard(revision.id());
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // If the cache contains a compatible wheel, return it.
         if let Some(built_wheel) = BuiltWheelMetadata::find_in_cache(tags, &cache_shard) {
             return Ok(built_wheel);
@@ -781,6 +805,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
             });
         }
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // Otherwise, we need to build a wheel.
         let task = self
             .reporter
@@ -897,6 +929,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
         // freshness, since entries have to be fresher than the revision itself.
         let cache_shard = cache_shard.shard(revision.id());
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // If the cache contains a compatible wheel, return it.
         if let Some(built_wheel) = BuiltWheelMetadata::find_in_cache(tags, &cache_shard) {
             return Ok(built_wheel);
@@ -1020,6 +1060,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
             ));
         }
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // Otherwise, we need to build a wheel.
         let task = self
             .reporter
@@ -1131,6 +1179,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
 
         let _lock = lock_shard(&cache_shard).await?;
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // If the cache contains a compatible wheel, return it.
         if let Some(built_wheel) = BuiltWheelMetadata::find_in_cache(tags, &cache_shard) {
             return Ok(built_wheel);
@@ -1257,6 +1313,14 @@ impl<'a, T: BuildContext> SourceDistributionBuilder<'a, T> {
             ));
         }
 
+        // If there are build settings, we need to scope to a cache shard.
+        let config_settings = self.build_context.config_settings();
+        let cache_shard = if config_settings.is_empty() {
+            cache_shard
+        } else {
+            cache_shard.shard(cache_key::cache_digest(config_settings))
+        };
+
         // Otherwise, we need to build a wheel.
         let task = self
             .reporter