1 files changed, 131 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs
new file mode 100644
index 000000000..9826e1c70
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/replace_filter_map_next_with_find_map.rs
@@ -0,0 +1,131 @@
+use hir::{db::AstDatabase, InFile};
+use ide_db::source_change::SourceChange;
+use syntax::{
+    ast::{self, HasArgList},
+    AstNode, TextRange,
+};
+use text_edit::TextEdit;
+
+use crate::{fix, Assist, Diagnostic, DiagnosticsContext, Severity};
+
+// Diagnostic: replace-filter-map-next-with-find-map
+//
+// This diagnostic is triggered when `.filter_map(..).next()` is used, rather than the more concise `.find_map(..)`.
+pub(crate) fn replace_filter_map_next_with_find_map(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::ReplaceFilterMapNextWithFindMap,
+) -> Diagnostic {
+    Diagnostic::new(
+        "replace-filter-map-next-with-find-map",
+        "replace filter_map(..).next() with find_map(..)",
+        ctx.sema.diagnostics_display_range(InFile::new(d.file, d.next_expr.clone().into())).range,
+    )
+    .severity(Severity::WeakWarning)
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::ReplaceFilterMapNextWithFindMap,
+) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.file)?;
+    let next_expr = d.next_expr.to_node(&root);
+    let next_call = ast::MethodCallExpr::cast(next_expr.syntax().clone())?;
+
+    let filter_map_call = ast::MethodCallExpr::cast(next_call.receiver()?.syntax().clone())?;
+    let filter_map_name_range = filter_map_call.name_ref()?.ident_token()?.text_range();
+    let filter_map_args = filter_map_call.arg_list()?;
+
+    let range_to_replace =
+        TextRange::new(filter_map_name_range.start(), next_expr.syntax().text_range().end());
+    let replacement = format!("find_map{}", filter_map_args.syntax().text());
+    let trigger_range = next_expr.syntax().text_range();
+
+    let edit = TextEdit::replace(range_to_replace, replacement);
+
+    let source_change = SourceChange::from_text_edit(d.file.original_file(ctx.sema.db), edit);
+
+    Some(vec![fix(
+        "replace_with_find_map",
+        "Replace filter_map(..).next() with find_map()",
+        source_change,
+        trigger_range,
+    )])
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tests::{check_diagnostics, check_fix};
+
+    #[test]
+    fn replace_filter_map_next_with_find_map2() {
+        check_diagnostics(
+            r#"
+//- minicore: iterators
+fn foo() {
+    let m = core::iter::repeat(()).filter_map(|()| Some(92)).next();
+}         //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 💡 weak: replace filter_map(..).next() with find_map(..)
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_without_next() {
+        check_diagnostics(
+            r#"
+//- minicore: iterators
+fn foo() {
+    let m = core::iter::repeat(())
+        .filter_map(|()| Some(92))
+        .count();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_with_intervening_methods() {
+        check_diagnostics(
+            r#"
+//- minicore: iterators
+fn foo() {
+    let m = core::iter::repeat(())
+        .filter_map(|()| Some(92))
+        .map(|x| x + 2)
+        .next();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_filter_map_next_with_find_map_no_diagnostic_if_not_in_chain() {
+        check_diagnostics(
+            r#"
+//- minicore: iterators
+fn foo() {
+    let m = core::iter::repeat(())
+        .filter_map(|()| Some(92));
+    let n = m.next();
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn replace_with_find_map() {
+        check_fix(
+            r#"
+//- minicore: iterators
+fn foo() {
+    let m = core::iter::repeat(()).$0filter_map(|()| Some(92)).next();
+}
+"#,
+            r#"
+fn foo() {
+    let m = core::iter::repeat(()).find_map(|()| Some(92));
+}
+"#,
+        )
+    }
+}