Add `track_caller` attributes to trace origin of Clippy lints

This allows the use of `-Z track-diagnostics` to see the origin of
Clippy lints emission, as is already the case for lints coming from
rustc.

2 files changed, 51 insertions, 0 deletions

diff --git a/src/tools/clippy/tests/ui/track-diagnostics-clippy.rs b/src/tools/clippy/tests/ui/track-diagnostics-clippy.rs
new file mode 100644
index 00000000000..2e67fb65efc
--- /dev/null
+++ b/src/tools/clippy/tests/ui/track-diagnostics-clippy.rs
@@ -0,0 +1,22 @@
+//@compile-flags: -Z track-diagnostics
+//@no-rustfix
+
+// Normalize the emitted location so this doesn't need
+// updating everytime someone adds or removes a line.
+//@normalize-stderr-test: ".rs:\d+:\d+" -> ".rs:LL:CC"
+
+#![warn(clippy::let_and_return, clippy::unnecessary_cast)]
+
+fn main() {
+    // Check the provenance of a lint sent through `LintContext::span_lint()`
+    let a = 3u32;
+    let b = a as u32;
+    //~^ unnecessary_cast
+    
+    // Check the provenance of a lint sent through `TyCtxt::node_span_lint()`
+    let c = {
+        let d = 42;
+        d
+        //~^ let_and_return
+    };
+}
diff --git a/src/tools/clippy/tests/ui/track-diagnostics-clippy.stderr b/src/tools/clippy/tests/ui/track-diagnostics-clippy.stderr
new file mode 100644
index 00000000000..f3aca685417
--- /dev/null
+++ b/src/tools/clippy/tests/ui/track-diagnostics-clippy.stderr
@@ -0,0 +1,29 @@
+error: casting to the same type is unnecessary (`u32` -> `u32`)
+  --> tests/ui/track-diagnostics-clippy.rs:LL:CC
+   |
+LL |     let b = a as u32;
+   |             ^^^^^^^^ help: try: `a`
+-Ztrack-diagnostics: created at src/tools/clippy/clippy_lints/src/casts/unnecessary_cast.rs:LL:CC
+   |
+   = note: `-D clippy::unnecessary-cast` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unnecessary_cast)]`
+
+error: returning the result of a `let` binding from a block
+  --> tests/ui/track-diagnostics-clippy.rs:LL:CC
+   |
+LL |         let d = 42;
+   |         ----------- unnecessary `let` binding
+LL |         d
+   |         ^
+-Ztrack-diagnostics: created at src/tools/clippy/clippy_lints/src/returns.rs:LL:CC
+   |
+   = note: `-D clippy::let-and-return` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::let_and_return)]`
+help: return the expression directly
+   |
+LL ~         
+LL ~         42
+   |
+
+error: aborting due to 2 previous errors
+