fix: Check enum categories when reading csv

crates/polars-core/src/chunked_array/logical/categorical/builder.rs

@@ -54,6 +54,48 @@ impl CategoricalChunkedBuilder {
         }
     }
 
+    fn try_get_cat_idx(&mut self, s: &str, h: u64) -> Option<u32> {
+        // SAFETY: index in hashmap are within bounds of categories
+        unsafe {
+            let r = self.local_mapping.entry(
+                h,
+                |k| self.categories.value_unchecked(*k as usize) == s,
+                |k| {
+                    self.local_hasher
+                        .hash_one(self.categories.value_unchecked(*k as usize))
+                },
+            );
+
+            match r {
+                HTEntry::Occupied(v) => Some(*v.get()),
+                HTEntry::Vacant(_) => None,
+            }
+        }
+    }
+
+    /// Append a new category, but fail if it didn't exist yet in the category state.
+    /// You can register categories up front with `register_value`, or via `append`.
+    #[inline]
+    pub fn try_append_value(&mut self, s: &str) -> PolarsResult<()> {
+        let h = self.local_hasher.hash_one(s);
+        let idx = self.try_get_cat_idx(s, h).ok_or_else(
+            || polars_err!(ComputeError: "category {} doesn't exist in Enum dtype", s),
+        )?;
+        self.cat_builder.push(Some(idx));
+        Ok(())
+    }
+
+    /// Append a new category, but fail if it didn't exist yet in the category state.
+    /// You can register categories up front with `register_value`, or via `append`.
+    #[inline]
+    pub fn try_append(&mut self, opt_s: Option<&str>) -> PolarsResult<()> {
+        match opt_s {
+            None => self.append_null(),
+            Some(s) => self.try_append_value(s)?,
+        }
+        Ok(())
+    }
+
     /// Registers a value to a categorical index without pushing it.
     /// Returns the index and if the value was new.
     #[inline]

crates/polars-io/src/csv/read/buffer.rs

@@ -309,7 +309,6 @@ impl CategoricalField {
             self.builder.append_null();
             return Ok(());
         }
-
         if validate_utf8(bytes) {
             if needs_escaping {
                 polars_ensure!(bytes.len() > 1, ComputeError: "invalid csv file\n\nField `{}` is not properly escaped.", std::str::from_utf8(bytes).map_err(to_compute_err)?);
@@ -329,13 +328,19 @@ impl CategoricalField {
                 // SAFETY:
                 // just did utf8 check
                 let key = unsafe { std::str::from_utf8_unchecked(&self.escape_scratch) };
-                self.builder.append_value(key);
+                if self.is_enum {
+                    self.builder.try_append_value(key)?;
+                } else {
+                    self.builder.append_value(key);
+                }
             } else {
                 // SAFETY:
                 // just did utf8 check
-                unsafe {
-                    self.builder
-                        .append_value(std::str::from_utf8_unchecked(bytes))
+                let key = unsafe { std::str::from_utf8_unchecked(bytes) };
+                if self.is_enum {
+                    self.builder.try_append_value(key)?
+                } else {
+                    self.builder.append_value(key)
                 }
             }
         } else if ignore_errors {

py-polars/tests/unit/io/test_csv.py

@@ -2526,3 +2526,17 @@ def test_header_only_column_selection_17173() -> None:
     result = pl.read_csv(io.StringIO(csv), columns=["B"])
     expected = pl.Series("B", [], pl.String()).to_frame()
     assert_frame_equal(result, expected)
+
+
+def test_csv_enum_raise() -> None:
+    ENUM_DTYPE = pl.Enum(["foo", "bar"])
+    with (
+        io.StringIO("col\nfoo\nbaz\n") as csv,
+        pytest.raises(
+            pl.exceptions.ComputeError, match="category baz doesn't exist in Enum dtype"
+        ),
+    ):
+        pl.read_csv(
+            csv,
+            schema={"col": ENUM_DTYPE},
+        )