1 files changed, 110 insertions, 0 deletions

diff --git a/crates/ide_diagnostics/src/handlers/unresolved_module.rs b/crates/ide_diagnostics/src/handlers/unresolved_module.rs
new file mode 100644
index 000000000..17166a0c6
--- /dev/null
+++ b/crates/ide_diagnostics/src/handlers/unresolved_module.rs
@@ -0,0 +1,110 @@
+use hir::db::AstDatabase;
+use ide_db::{assists::Assist, base_db::AnchoredPathBuf, source_change::FileSystemEdit};
+use syntax::AstNode;
+
+use crate::{fix, Diagnostic, DiagnosticsContext};
+
+// Diagnostic: unresolved-module
+//
+// This diagnostic is triggered if rust-analyzer is unable to discover referred module.
+pub(crate) fn unresolved_module(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::UnresolvedModule,
+) -> Diagnostic {
+    Diagnostic::new(
+        "unresolved-module",
+        "unresolved module",
+        ctx.sema.diagnostics_display_range(d.decl.clone().map(|it| it.into())).range,
+    )
+    .with_fixes(fixes(ctx, d))
+}
+
+fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::UnresolvedModule) -> Option<Vec<Assist>> {
+    let root = ctx.sema.db.parse_or_expand(d.decl.file_id)?;
+    let unresolved_module = d.decl.value.to_node(&root);
+    Some(vec![fix(
+        "create_module",
+        "Create module",
+        FileSystemEdit::CreateFile {
+            dst: AnchoredPathBuf {
+                anchor: d.decl.file_id.original_file(ctx.sema.db),
+                path: d.candidate.clone(),
+            },
+            initial_contents: "".to_string(),
+        }
+        .into(),
+        unresolved_module.syntax().text_range(),
+    )])
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::expect;
+
+    use crate::tests::{check_diagnostics, check_expect};
+
+    #[test]
+    fn unresolved_module() {
+        check_diagnostics(
+            r#"
+//- /lib.rs
+mod foo;
+  mod bar;
+//^^^^^^^^ unresolved module
+mod baz {}
+//- /foo.rs
+"#,
+        );
+    }
+
+    #[test]
+    fn test_unresolved_module_diagnostic() {
+        check_expect(
+            r#"mod foo;"#,
+            expect![[r#"
+                [
+                    Diagnostic {
+                        code: DiagnosticCode(
+                            "unresolved-module",
+                        ),
+                        message: "unresolved module",
+                        range: 0..8,
+                        severity: Error,
+                        unused: false,
+                        experimental: false,
+                        fixes: Some(
+                            [
+                                Assist {
+                                    id: AssistId(
+                                        "create_module",
+                                        QuickFix,
+                                    ),
+                                    label: "Create module",
+                                    group: None,
+                                    target: 0..8,
+                                    source_change: Some(
+                                        SourceChange {
+                                            source_file_edits: {},
+                                            file_system_edits: [
+                                                CreateFile {
+                                                    dst: AnchoredPathBuf {
+                                                        anchor: FileId(
+                                                            0,
+                                                        ),
+                                                        path: "foo.rs",
+                                                    },
+                                                    initial_contents: "",
+                                                },
+                                            ],
+                                            is_snippet: false,
+                                        },
+                                    ),
+                                },
+                            ],
+                        ),
+                    },
+                ]
+            "#]],
+        );
+    }
+}