Significantly more glorious marks

Author: matklad

crates/ra_assists/src/handlers/add_turbo_fish.rs

@@ -1,11 +1,11 @@
 use ra_ide_db::defs::{classify_name_ref, Definition, NameRefClass};
 use ra_syntax::{ast, AstNode, SyntaxKind, T};
+use test_utils::mark;
 
 use crate::{
     assist_context::{AssistContext, Assists},
     AssistId,
 };
-use test_utils::tested_by;
 
 // Assist: add_turbo_fish
 //
@@ -28,7 +28,7 @@ pub(crate) fn add_turbo_fish(acc: &mut Assists, ctx: &AssistContext) -> Option<(
     let ident = ctx.find_token_at_offset(SyntaxKind::IDENT)?;
     let next_token = ident.next_token()?;
     if next_token.kind() == T![::] {
-        tested_by!(add_turbo_fish_one_fish_is_enough);
+        mark::hit!(add_turbo_fish_one_fish_is_enough);
         return None;
     }
     let name_ref = ast::NameRef::cast(ident.parent())?;
@@ -42,7 +42,7 @@ pub(crate) fn add_turbo_fish(acc: &mut Assists, ctx: &AssistContext) -> Option<(
     };
     let generics = hir::GenericDef::Function(fun).params(ctx.sema.db);
     if generics.is_empty() {
-        tested_by!(add_turbo_fish_non_generic);
+        mark::hit!(add_turbo_fish_non_generic);
         return None;
     }
     acc.add(AssistId("add_turbo_fish"), "Add `::<>`", ident.text_range(), |builder| {
@@ -58,7 +58,7 @@ mod tests {
     use crate::tests::{check_assist, check_assist_not_applicable};
 
     use super::*;
-    use test_utils::covers;
+    use test_utils::mark;
 
     #[test]
     fn add_turbo_fish_function() {
@@ -106,7 +106,7 @@ fn main() {
 
     #[test]
     fn add_turbo_fish_one_fish_is_enough() {
-        covers!(add_turbo_fish_one_fish_is_enough);
+        mark::check!(add_turbo_fish_one_fish_is_enough);
         check_assist_not_applicable(
             add_turbo_fish,
             r#"
@@ -120,7 +120,7 @@ fn main() {
 
     #[test]
     fn add_turbo_fish_non_generic() {
-        covers!(add_turbo_fish_non_generic);
+        mark::check!(add_turbo_fish_non_generic);
         check_assist_not_applicable(
             add_turbo_fish,
             r#"

crates/ra_assists/src/marks.rs

@@ -10,6 +10,4 @@ test_utils::marks![
     test_not_applicable_if_variable_unused
     change_visibility_field_false_positive
     test_add_from_impl_already_exists
-    add_turbo_fish_one_fish_is_enough
-    add_turbo_fish_non_generic
 ];

crates/test_utils/src/lib.rs

@@ -8,6 +8,8 @@
 
 #[macro_use]
 pub mod marks;
+#[macro_use]
+pub mod mark;
 
 use std::{
     fs,

crates/test_utils/src/mark.rs

@@ -0,0 +1,78 @@
+//! This module implements manually tracked test coverage, which is useful for
+//! quickly finding a test responsible for testing a particular bit of code.
+//!
+//! See <https://matklad.github.io/2018/06/18/a-trick-for-test-maintenance.html>
+//! for details, but the TL;DR is that you write your test as
+//!
+//! ```
+//! #[test]
+//! fn test_foo() {
+//!     mark::check!(test_foo);
+//! }
+//! ```
+//!
+//! and in the code under test you write
+//!
+//! ```
+//! # use test_utils::mark;
+//! # fn some_condition() -> bool { true }
+//! fn foo() {
+//!     if some_condition() {
+//!         mark::hit!(test_foo);
+//!     }
+//! }
+//! ```
+//!
+//! This module then checks that executing the test indeed covers the specified
+//! function. This is useful if you come back to the `foo` function ten years
+//! later and wonder where the test are: now you can grep for `test_foo`.
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+#[macro_export]
+macro_rules! _hit {
+    ($ident:ident) => {{
+        #[cfg(test)]
+        {
+            extern "C" {
+                #[no_mangle]
+                static $ident: std::sync::atomic::AtomicUsize;
+            }
+            unsafe {
+                $ident.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
+            }
+        }
+    }};
+}
+pub use _hit as hit;
+
+#[macro_export]
+macro_rules! _check {
+    ($ident:ident) => {
+        #[no_mangle]
+        static $ident: std::sync::atomic::AtomicUsize = std::sync::atomic::AtomicUsize::new(0);
+        let _checker = $crate::mark::MarkChecker::new(&$ident);
+    };
+}
+pub use _check as check;
+
+pub struct MarkChecker {
+    mark: &'static AtomicUsize,
+    value_on_entry: usize,
+}
+
+impl MarkChecker {
+    pub fn new(mark: &'static AtomicUsize) -> MarkChecker {
+        let value_on_entry = mark.load(Ordering::SeqCst);
+        MarkChecker { mark, value_on_entry }
+    }
+}
+
+impl Drop for MarkChecker {
+    fn drop(&mut self) {
+        if std::thread::panicking() {
+            return;
+        }
+        let value_on_exit = self.mark.load(Ordering::SeqCst);
+        assert!(value_on_exit > self.value_on_entry, "mark was not hit")
+    }
+}