Reject `--editable` flag on non-directory requirements (#10994)

## Summary

Closes https://github.com/astral-sh/uv/issues/10992.

crates/uv-workspace/src/pyproject.rs

@@ -1312,6 +1312,10 @@ pub enum SourceError {
     UnusedTag(String, String),
     #[error("`{0}` did not resolve to a Git repository, but a Git reference (`--branch {1}`) was provided.")]
     UnusedBranch(String, String),
+    #[error("`{0}` did not resolve to a local directory, but the `--editable` flag was provided. Editable installs are only supported for local directories.")]
+    UnusedEditable(String),
+    #[error("Workspace dependency `{0}` was marked as `--no-editable`, but workspace dependencies are always added in editable mode. Pass `--no-editable` to `uv sync` or `uv run` to install workspace dependencies in non-editable mode.")]
+    UnusedNoEditable(String),
     #[error("Failed to resolve absolute path")]
     Absolute(#[from] std::io::Error),
     #[error("Path contains invalid characters: `{}`", _0.display())]
@@ -1349,6 +1353,20 @@ impl Source {
             }
         }
 
+        if workspace {
+            // If a workspace source is added with `--no-editable`, error.
+            if editable == Some(false) {
+                return Err(SourceError::UnusedNoEditable(name.to_string()));
+            }
+        } else {
+            // If we resolved a non-path source, and user specified an `--editable` flag, error.
+            if !matches!(source, RequirementSource::Directory { .. }) {
+                if editable == Some(true) {
+                    return Err(SourceError::UnusedEditable(name.to_string()));
+                }
+            }
+        }
+
         // If the source is a workspace package, error if the user tried to specify a source.
         if workspace {
             return match source {

crates/uv/tests/it/edit.rs

@@ -875,6 +875,37 @@ fn add_raw_error() -> Result<()> {
     Ok(())
 }
 
+#[test]
+#[cfg(feature = "git")]
+fn add_editable_error() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(indoc! {r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = []
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+    "#})?;
+
+    // Provide `--editable` with a non-source tree.
+    uv_snapshot!(context.filters(), context.add().arg("flask @ https://files.pythonhosted.org/packages/61/80/ffe1da13ad9300f87c93af113edd0638c75138c42a0994becfacac078c06/flask-3.0.3-py3-none-any.whl").arg("--editable"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: `flask` did not resolve to a local directory, but the `--editable` flag was provided. Editable installs are only supported for local directories.
+    "###);
+
+    Ok(())
+}
+
 /// Add an unnamed requirement.
 #[test]
 #[cfg(feature = "git")]
@@ -2186,6 +2217,24 @@ fn add_workspace_editable() -> Result<()> {
     "#})?;
 
     let child1 = context.temp_dir.join("child1");
+
+    // `--no-editable` should error.
+    let mut add_cmd = context.add();
+    add_cmd
+        .arg("child2")
+        .arg("--no-editable")
+        .current_dir(&child1);
+
+    uv_snapshot!(context.filters(), add_cmd, @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    error: Workspace dependency `child2` was marked as `--no-editable`, but workspace dependencies are always added in editable mode. Pass `--no-editable` to `uv sync` or `uv run` to install workspace dependencies in non-editable mode.
+    "###);
+
+    // `--editable` should not.
     let mut add_cmd = context.add();
     add_cmd.arg("child2").arg("--editable").current_dir(&child1);