1 files changed, 156 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/unresolved_module.rs b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/unresolved_module.rs
new file mode 100644
index 000000000..b8f2a9e94
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/ide-diagnostics/src/handlers/unresolved_module.rs
@@ -0,0 +1,156 @@
+use hir::db::AstDatabase;
+use ide_db::{assists::Assist, base_db::AnchoredPathBuf, source_change::FileSystemEdit};
+use itertools::Itertools;
+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",
+        match &*d.candidates {
+            [] => "unresolved module".to_string(),
+            [candidate] => format!("unresolved module, can't find module file: {}", candidate),
+            [candidates @ .., last] => {
+                format!(
+                    "unresolved module, can't find module file: {}, or {}",
+                    candidates.iter().format(", "),
+                    last
+                )
+            }
+        },
+        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(
+        d.candidates
+            .iter()
+            .map(|candidate| {
+                fix(
+                    "create_module",
+                    &format!("Create module at `{candidate}`"),
+                    FileSystemEdit::CreateFile {
+                        dst: AnchoredPathBuf {
+                            anchor: d.decl.file_id.original_file(ctx.sema.db),
+                            path: candidate.clone(),
+                        },
+                        initial_contents: "".to_string(),
+                    }
+                    .into(),
+                    unresolved_module.syntax().text_range(),
+                )
+            })
+            .collect(),
+    )
+}
+
+#[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;
+//^^^^^^^^ 💡 error: unresolved module, can't find module file: bar.rs, or bar/mod.rs
+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, can't find module file: foo.rs, or foo/mod.rs",
+                        range: 0..8,
+                        severity: Error,
+                        unused: false,
+                        experimental: false,
+                        fixes: Some(
+                            [
+                                Assist {
+                                    id: AssistId(
+                                        "create_module",
+                                        QuickFix,
+                                    ),
+                                    label: "Create module at `foo.rs`",
+                                    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,
+                                        },
+                                    ),
+                                    trigger_signature_help: false,
+                                },
+                                Assist {
+                                    id: AssistId(
+                                        "create_module",
+                                        QuickFix,
+                                    ),
+                                    label: "Create module at `foo/mod.rs`",
+                                    group: None,
+                                    target: 0..8,
+                                    source_change: Some(
+                                        SourceChange {
+                                            source_file_edits: {},
+                                            file_system_edits: [
+                                                CreateFile {
+                                                    dst: AnchoredPathBuf {
+                                                        anchor: FileId(
+                                                            0,
+                                                        ),
+                                                        path: "foo/mod.rs",
+                                                    },
+                                                    initial_contents: "",
+                                                },
+                                            ],
+                                            is_snippet: false,
+                                        },
+                                    ),
+                                    trigger_signature_help: false,
+                                },
+                            ],
+                        ),
+                    },
+                ]
+            "#]],
+        );
+    }
+}