Recommend [project] table in uv add for non-project directories

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

@@ -201,13 +201,14 @@ pub(crate) async fn add(
         };
 
         // For non-project workspace roots, allow dev dependencies, but nothing else.
+        // TODO(charlie): Automatically "upgrade" the project by adding a `[project]` table.
         if project.is_non_project() {
             match dependency_type {
                 DependencyType::Production => {
-                    bail!("Found a non-project workspace root; production dependencies are unsupported (instead, use: `{}`)", "uv add --dev".green())
+                    bail!("Project is missing a `[project]` table; add a `[project]` table to support production dependencies, or use `{}`", "uv add --dev".green())
                 }
                 DependencyType::Optional(_) => {
-                    bail!("Found a non-project workspace root; optional dependencies are unsupported (instead, use: `{}`)", "uv add --dev".green())
+                    bail!("Project is missing a `[project]` table; add a `[project]` table to support optional dependencies, or use `{}`", "uv add --dev".green())
                 }
                 DependencyType::Dev => (),
             }

crates/uv/tests/edit.rs

@@ -3530,7 +3530,7 @@ fn add_non_project() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    error: Found a non-project workspace root; production dependencies are unsupported (instead, use: `uv add --dev`)
+    error: Project is missing a `[project]` table; add a `[project]` table to support production dependencies, or use `uv add --dev`
     "###);
 
     // Adding `iniconfig` as optional should fail, since virtual workspace roots don't support
@@ -3541,7 +3541,7 @@ fn add_non_project() -> Result<()> {
     ----- stdout -----
 
     ----- stderr -----
-    error: Found a non-project workspace root; optional dependencies are unsupported (instead, use: `uv add --dev`)
+    error: Project is missing a `[project]` table; add a `[project]` table to support optional dependencies, or use `uv add --dev`
     "###);
 
     // Adding `iniconfig` as a dev dependency should succeed.