1 files changed, 240 insertions, 0 deletions

diff --git a/crates/ide_assists/src/handlers/generate_enum_match_method.rs b/crates/ide_assists/src/handlers/generate_enum_match_method.rs
new file mode 100644
index 000000000..aeb887e71
--- /dev/null
+++ b/crates/ide_assists/src/handlers/generate_enum_match_method.rs
@@ -0,0 +1,240 @@
+use stdx::{format_to, to_lower_snake_case};
+use syntax::ast::VisibilityOwner;
+use syntax::ast::{self, AstNode, NameOwner};
+use test_utils::mark;
+
+use crate::{
+    utils::{find_impl_block_end, find_struct_impl, generate_impl_text},
+    AssistContext, AssistId, AssistKind, Assists,
+};
+
+// Assist: generate_enum_match_method
+//
+// Generate an `is_` method for an enum variant.
+//
+// ```
+// enum Version {
+//  Undefined,
+//  Minor$0,
+//  Major,
+// }
+// ```
+// ->
+// ```
+// enum Version {
+//  Undefined,
+//  Minor,
+//  Major,
+// }
+//
+// impl Version {
+//     /// Returns `true` if the version is [`Minor`].
+//     fn is_minor(&self) -> bool {
+//         matches!(self, Self::Minor)
+//     }
+// }
+// ```
+pub(crate) fn generate_enum_match_method(acc: &mut Assists, ctx: &AssistContext) -> Option<()> {
+    let variant = ctx.find_node_at_offset::<ast::Variant>()?;
+    let variant_name = variant.name()?;
+    let parent_enum = variant.parent_enum();
+    if !matches!(variant.kind(), ast::StructKind::Unit) {
+        mark::hit!(test_gen_enum_match_on_non_unit_variant_not_implemented);
+        return None;
+    }
+
+    let enum_lowercase_name = to_lower_snake_case(&parent_enum.name()?.to_string());
+    let fn_name = to_lower_snake_case(&variant_name.to_string());
+
+    // Return early if we've found an existing new fn
+    let impl_def = find_struct_impl(
+        &ctx,
+        &ast::Adt::Enum(parent_enum.clone()),
+        format!("is_{}", fn_name).as_str(),
+    )?;
+
+    let target = variant.syntax().text_range();
+    acc.add(
+        AssistId("generate_enum_match_method", AssistKind::Generate),
+        "Generate an `is_` method for an enum variant",
+        target,
+        |builder| {
+            let mut buf = String::with_capacity(512);
+
+            if impl_def.is_some() {
+                buf.push('\n');
+            }
+
+            let vis = parent_enum.visibility().map_or(String::new(), |v| format!("{} ", v));
+            format_to!(
+                buf,
+                "    /// Returns `true` if the {} is [`{}`].
+    {}fn is_{}(&self) -> bool {{
+        matches!(self, Self::{})
+    }}",
+                enum_lowercase_name,
+                variant_name,
+                vis,
+                fn_name,
+                variant_name
+            );
+
+            let start_offset = impl_def
+                .and_then(|impl_def| find_impl_block_end(impl_def, &mut buf))
+                .unwrap_or_else(|| {
+                    buf = generate_impl_text(&ast::Adt::Enum(parent_enum.clone()), &buf);
+                    parent_enum.syntax().text_range().end()
+                });
+
+            builder.insert(start_offset, buf);
+        },
+    )
+}
+
+#[cfg(test)]
+mod tests {
+    use test_utils::mark;
+
+    use crate::tests::{check_assist, check_assist_not_applicable};
+
+    use super::*;
+
+    fn check_not_applicable(ra_fixture: &str) {
+        check_assist_not_applicable(generate_enum_match_method, ra_fixture)
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant() {
+        check_assist(
+            generate_enum_match_method,
+            r#"
+enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}"#,
+            r#"enum Variant {
+    Undefined,
+    Minor,
+    Major,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_already_implemented() {
+        check_not_applicable(
+            r#"
+enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}
+
+impl Variant {
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_add_from_impl_no_element() {
+        mark::check!(test_gen_enum_match_on_non_unit_variant_not_implemented);
+        check_not_applicable(
+            r#"
+enum Variant {
+    Undefined,
+    Minor(u32)$0,
+    Major,
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant_with_one_variant() {
+        check_assist(
+            generate_enum_match_method,
+            r#"enum Variant { Undefi$0ned }"#,
+            r#"
+enum Variant { Undefined }
+
+impl Variant {
+    /// Returns `true` if the variant is [`Undefined`].
+    fn is_undefined(&self) -> bool {
+        matches!(self, Self::Undefined)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_generate_enum_match_from_variant_with_visibility_marker() {
+        check_assist(
+            generate_enum_match_method,
+            r#"
+pub(crate) enum Variant {
+    Undefined,
+    Minor$0,
+    Major,
+}"#,
+            r#"pub(crate) enum Variant {
+    Undefined,
+    Minor,
+    Major,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    pub(crate) fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+        );
+    }
+
+    #[test]
+    fn test_multiple_generate_enum_match_from_variant() {
+        check_assist(
+            generate_enum_match_method,
+            r#"
+enum Variant {
+    Undefined,
+    Minor,
+    Major$0,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+}"#,
+            r#"enum Variant {
+    Undefined,
+    Minor,
+    Major,
+}
+
+impl Variant {
+    /// Returns `true` if the variant is [`Minor`].
+    fn is_minor(&self) -> bool {
+        matches!(self, Self::Minor)
+    }
+
+    /// Returns `true` if the variant is [`Major`].
+    fn is_major(&self) -> bool {
+        matches!(self, Self::Major)
+    }
+}"#,
+        );
+    }
+}