Set --dev to default for uv run and uv sync (#4118)

## Summary

Closes #4117.

crates/uv/src/cli.rs

@@ -1691,10 +1691,11 @@ pub(crate) struct RunArgs {
     pub(crate) no_all_extras: bool,
 
     /// Include development dependencies.
-    #[arg(long, overrides_with("no_dev"))]
+    #[arg(long, overrides_with("no_dev"), hide = true)]
     pub(crate) dev: bool,
 
-    #[arg(long, conflicts_with("offline"), overrides_with("dev"), hide = true)]
+    /// Omit development dependencies.
+    #[arg(long, overrides_with("dev"))]
     pub(crate) no_dev: bool,
 
     /// The command to run.
@@ -1779,10 +1780,11 @@ pub(crate) struct SyncArgs {
     pub(crate) no_all_extras: bool,
 
     /// Include development dependencies.
-    #[arg(long, overrides_with("no_dev"))]
+    #[arg(long, overrides_with("no_dev"), hide = true)]
     pub(crate) dev: bool,
 
-    #[arg(long, conflicts_with("offline"), overrides_with("dev"), hide = true)]
+    /// Omit development dependencies.
+    #[arg(long, overrides_with("dev"))]
     pub(crate) no_dev: bool,
 
     /// Refresh all cached data.

crates/uv/src/settings.rs

@@ -170,7 +170,7 @@ impl RunSettings {
                 flag(all_extras, no_all_extras).unwrap_or_default(),
                 extra.unwrap_or_default(),
             ),
-            dev: flag(dev, no_dev).unwrap_or(false),
+            dev: flag(dev, no_dev).unwrap_or(true),
             target,
             args,
             with,
@@ -278,7 +278,7 @@ impl SyncSettings {
                 flag(all_extras, no_all_extras).unwrap_or_default(),
                 extra.unwrap_or_default(),
             ),
-            dev: flag(dev, no_dev).unwrap_or(false),
+            dev: flag(dev, no_dev).unwrap_or(true),
             python,
         }
     }
@@ -445,7 +445,6 @@ impl PipCompileSettings {
                 PipOptions {
                     python,
                     system: flag(system, no_system),
-
                     index_url: index_args.index_url.and_then(Maybe::into_option),
                     extra_index_url: index_args.extra_index_url.map(|extra_index_urls| {
                         extra_index_urls

crates/uv/tests/lock.rs

@@ -1891,7 +1891,7 @@ fn lock_dev() -> Result<()> {
     });
 
     // Install from the lockfile, excluding development dependencies.
-    uv_snapshot!(context.filters(), context.sync(), @r###"
+    uv_snapshot!(context.filters(), context.sync().arg("--no-dev"), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -1904,8 +1904,8 @@ fn lock_dev() -> Result<()> {
      + project==0.1.0 (from file://[TEMP_DIR]/)
     "###);
 
-    // Install from the lockfile, including development dependencies.
-    uv_snapshot!(context.filters(), context.sync().arg("--dev"), @r###"
+    // Install from the lockfile, including development dependencies (the default).
+    uv_snapshot!(context.filters(), context.sync(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----