1 files changed, 65 insertions, 0 deletions
diff --git a/compiler/rustc_ast_passes/src/show_span.rs b/compiler/rustc_ast_passes/src/show_span.rs
new file mode 100644
index 000000000..27637e311
--- /dev/null
+++ b/compiler/rustc_ast_passes/src/show_span.rs
@@ -0,0 +1,65 @@
+//! Span debugger
+//!
+//! This module shows spans for all expressions in the crate
+//! to help with compiler debugging.
+
+use std::str::FromStr;
+
+use rustc_ast as ast;
+use rustc_ast::visit;
+use rustc_ast::visit::Visitor;
+
+enum Mode {
+    Expression,
+    Pattern,
+    Type,
+}
+
+impl FromStr for Mode {
+    type Err = ();
+    fn from_str(s: &str) -> Result<Mode, ()> {
+        let mode = match s {
+            "expr" => Mode::Expression,
+            "pat" => Mode::Pattern,
+            "ty" => Mode::Type,
+            _ => return Err(()),
+        };
+        Ok(mode)
+    }
+}
+
+struct ShowSpanVisitor<'a> {
+    span_diagnostic: &'a rustc_errors::Handler,
+    mode: Mode,
+}
+
+impl<'a> Visitor<'a> for ShowSpanVisitor<'a> {
+    fn visit_expr(&mut self, e: &'a ast::Expr) {
+        if let Mode::Expression = self.mode {
+            self.span_diagnostic.span_warn(e.span, "expression");
+        }
+        visit::walk_expr(self, e);
+    }
+
+    fn visit_pat(&mut self, p: &'a ast::Pat) {
+        if let Mode::Pattern = self.mode {
+            self.span_diagnostic.span_warn(p.span, "pattern");
+        }
+        visit::walk_pat(self, p);
+    }
+
+    fn visit_ty(&mut self, t: &'a ast::Ty) {
+        if let Mode::Type = self.mode {
+            self.span_diagnostic.span_warn(t.span, "type");
+        }
+        visit::walk_ty(self, t);
+    }
+}
+
+pub fn run(span_diagnostic: &rustc_errors::Handler, mode: &str, krate: &ast::Crate) {
+    let Ok(mode) = mode.parse() else {
+        return;
+    };
+    let mut v = ShowSpanVisitor { span_diagnostic, mode };
+    visit::walk_crate(&mut v, krate);
+}