1 files changed, 113 insertions, 0 deletions

diff --git a/crates/ide/src/diagnostics/inactive_code.rs b/crates/ide/src/diagnostics/inactive_code.rs
new file mode 100644
index 000000000..52f97cb4c
--- /dev/null
+++ b/crates/ide/src/diagnostics/inactive_code.rs
@@ -0,0 +1,113 @@
+use cfg::DnfExpr;
+use stdx::format_to;
+
+use crate::diagnostics::{Diagnostic, DiagnosticsContext};
+
+// Diagnostic: inactive-code
+//
+// This diagnostic is shown for code with inactive `#[cfg]` attributes.
+pub(super) fn inactive_code(
+    ctx: &DiagnosticsContext<'_>,
+    d: &hir::InactiveCode,
+) -> Option<Diagnostic> {
+    // If there's inactive code somewhere in a macro, don't propagate to the call-site.
+    if d.node.file_id.expansion_info(ctx.sema.db).is_some() {
+        return None;
+    }
+
+    let inactive = DnfExpr::new(d.cfg.clone()).why_inactive(&d.opts);
+    let mut message = "code is inactive due to #[cfg] directives".to_string();
+
+    if let Some(inactive) = inactive {
+        format_to!(message, ": {}", inactive);
+    }
+
+    let res = Diagnostic::new(
+        "inactive-code",
+        message,
+        ctx.sema.diagnostics_display_range(d.node.clone()).range,
+    )
+    .with_unused(true);
+    Some(res)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostics::tests::check_diagnostics_with_inactive_code;
+
+    #[test]
+    fn cfg_diagnostics() {
+        check_diagnostics_with_inactive_code(
+            r#"
+fn f() {
+    // The three g̶e̶n̶d̶e̶r̶s̶ statements:
+
+    #[cfg(a)] fn f() {}  // Item statement
+  //^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] {}         // Expression statement
+  //^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    #[cfg(a)] let x = 0; // let statement
+  //^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+
+    abc(#[cfg(a)] 0);
+      //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    let x = Struct {
+        #[cfg(a)] f: 0,
+      //^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    };
+    match () {
+        () => (),
+        #[cfg(a)] () => (),
+      //^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+    }
+
+    #[cfg(a)] 0          // Trailing expression of block
+  //^^^^^^^^^^^ code is inactive due to #[cfg] directives: a is disabled
+}
+        "#,
+            true,
+        );
+    }
+
+    #[test]
+    fn inactive_item() {
+        // Additional tests in `cfg` crate. This only tests disabled cfgs.
+
+        check_diagnostics_with_inactive_code(
+            r#"
+    #[cfg(no)] pub fn f() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no is disabled
+
+    #[cfg(no)] #[cfg(no2)] mod m;
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no and no2 are disabled
+
+    #[cfg(all(not(a), b))] enum E {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: b is disabled
+
+    #[cfg(feature = "std")] use std;
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: feature = "std" is disabled
+"#,
+            true,
+        );
+    }
+
+    /// Tests that `cfg` attributes behind `cfg_attr` is handled properly.
+    #[test]
+    fn inactive_via_cfg_attr() {
+        cov_mark::check!(cfg_attr_active);
+        check_diagnostics_with_inactive_code(
+            r#"
+    #[cfg_attr(not(never), cfg(no))] fn f() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no is disabled
+
+    #[cfg_attr(not(never), cfg(not(no)))] fn f() {}
+
+    #[cfg_attr(never, cfg(no))] fn g() {}
+
+    #[cfg_attr(not(never), inline, cfg(no))] fn h() {}
+  //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no is disabled
+"#,
+            true,
+        );
+    }
+}