1 files changed, 181 insertions, 0 deletions

diff --git a/crates/ra_assists/src/assists/auto_import.rs b/crates/ra_assists/src/assists/auto_import.rs
new file mode 100644
index 000000000..fe226521e
--- /dev/null
+++ b/crates/ra_assists/src/assists/auto_import.rs
@@ -0,0 +1,181 @@
+use hir::db::HirDatabase;
+use ra_syntax::{
+    ast::{self, AstNode},
+    SmolStr, SyntaxElement,
+    SyntaxKind::{NAME_REF, USE_ITEM},
+    SyntaxNode,
+};
+
+use crate::{
+    assist_ctx::{ActionBuilder, Assist, AssistCtx},
+    auto_import_text_edit, AssistId, ImportsLocator,
+};
+
+// Assist: auto_import
+//
+// If the name is unresolved, provides all possible imports for it.
+//
+// ```
+// fn main() {
+//     let map = HashMap<|>::new();
+// }
+// ```
+// ->
+// ```
+// use std::collections::HashMap;
+//
+// fn main() {
+//     let map = HashMap<|>::new();
+// }
+// ```
+pub(crate) fn auto_import<'a, F: ImportsLocator<'a>>(
+    ctx: AssistCtx<impl HirDatabase>,
+    imports_locator: &mut F,
+) -> Option<Assist> {
+    let path: ast::Path = ctx.find_node_at_offset()?;
+    let module = path.syntax().ancestors().find_map(ast::Module::cast);
+    let position = match module.and_then(|it| it.item_list()) {
+        Some(item_list) => item_list.syntax().clone(),
+        None => {
+            let current_file = path.syntax().ancestors().find_map(ast::SourceFile::cast)?;
+            current_file.syntax().clone()
+        }
+    };
+
+    let module_with_name_to_import = ctx.source_analyzer(&position, None).module()?;
+    let name_to_import = hir::InFile {
+        file_id: ctx.frange.file_id.into(),
+        value: &find_applicable_name_ref(ctx.covering_element())?,
+    };
+
+    let proposed_imports =
+        imports_locator.find_imports(name_to_import, module_with_name_to_import)?;
+    if proposed_imports.is_empty() {
+        return None;
+    }
+
+    ctx.add_assist_group(AssistId("auto_import"), "auto import", || {
+        proposed_imports
+            .into_iter()
+            .map(|import| import_to_action(import.to_string(), &position, &path))
+            .collect()
+    })
+}
+
+fn find_applicable_name_ref(element: SyntaxElement) -> Option<ast::NameRef> {
+    if element.ancestors().find(|ancestor| ancestor.kind() == USE_ITEM).is_some() {
+        None
+    } else if element.kind() == NAME_REF {
+        Some(element.as_node().cloned().and_then(ast::NameRef::cast)?)
+    } else {
+        let parent = element.parent()?;
+        if parent.kind() == NAME_REF {
+            Some(ast::NameRef::cast(parent)?)
+        } else {
+            None
+        }
+    }
+}
+
+fn import_to_action(import: String, position: &SyntaxNode, path: &ast::Path) -> ActionBuilder {
+    let mut action_builder = ActionBuilder::default();
+    action_builder.label(format!("Import `{}`", &import));
+    auto_import_text_edit(
+        position,
+        &path.syntax().clone(),
+        &[SmolStr::new(import)],
+        action_builder.text_edit_builder(),
+    );
+    action_builder
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::helpers::{
+        check_assist_with_imports_locator, check_assist_with_imports_locator_not_applicable,
+    };
+    use hir::Name;
+
+    #[derive(Clone)]
+    struct TestImportsLocator<'a> {
+        import_path: &'a [Name],
+    }
+
+    impl<'a> TestImportsLocator<'a> {
+        fn new(import_path: &'a [Name]) -> Self {
+            TestImportsLocator { import_path }
+        }
+    }
+
+    impl<'a> ImportsLocator<'_> for TestImportsLocator<'_> {
+        fn find_imports(
+            &mut self,
+            _: hir::InFile<&ast::NameRef>,
+            _: hir::Module,
+        ) -> Option<Vec<hir::ModPath>> {
+            if self.import_path.is_empty() {
+                None
+            } else {
+                Some(vec![hir::ModPath {
+                    kind: hir::PathKind::Plain,
+                    segments: self.import_path.to_owned(),
+                }])
+            }
+        }
+    }
+
+    #[test]
+    fn applicable_when_found_an_import() {
+        let import_path = &[hir::name::known::std, hir::name::known::ops, hir::name::known::Debug];
+        let mut imports_locator = TestImportsLocator::new(import_path);
+        check_assist_with_imports_locator(
+            auto_import,
+            &mut imports_locator,
+            "
+            fn main() {
+            }
+
+            Debug<|>",
+            &format!(
+                "
+            use {};
+
+            fn main() {{
+            }}
+
+            Debug<|>",
+                import_path
+                    .into_iter()
+                    .map(|name| name.to_string())
+                    .collect::<Vec<String>>()
+                    .join("::")
+            ),
+        );
+    }
+
+    #[test]
+    fn not_applicable_when_no_imports_found() {
+        let mut imports_locator = TestImportsLocator::new(&[]);
+        check_assist_with_imports_locator_not_applicable(
+            auto_import,
+            &mut imports_locator,
+            "
+            fn main() {
+            }
+
+            Debug<|>",
+        );
+    }
+
+    #[test]
+    fn not_applicable_in_import_statements() {
+        let import_path = &[hir::name::known::std, hir::name::known::ops, hir::name::known::Debug];
+        let mut imports_locator = TestImportsLocator::new(import_path);
+        check_assist_with_imports_locator_not_applicable(
+            auto_import,
+            &mut imports_locator,
+            "use Debug<|>;",
+        );
+    }
+}