Migrate "function cannot return without recursing" diagnostic

Cargo.lock

@@ -4070,6 +4070,7 @@ dependencies = [
  "rustc_hir",
  "rustc_index",
  "rustc_infer",
+ "rustc_macros",
  "rustc_middle",
  "rustc_serialize",
  "rustc_session",

compiler/rustc_error_messages/locales/en-US/mir_build.ftl

@@ -0,0 +1,5 @@
+mir_build_unconditional_recursion = function cannot return without recursing
+    .label = cannot return without recursing
+    .help = a `loop` may express intention better if this is on purpose
+
+mir_build_unconditional_recursion_call_site_label = recursive call site

compiler/rustc_error_messages/src/lib.rs

@@ -58,6 +58,7 @@
     metadata => "../locales/en-US/metadata.ftl",
     middle => "../locales/en-US/middle.ftl",
     mir_dataflow => "../locales/en-US/mir_dataflow.ftl",
+    mir_build => "../locales/en-US/mir_build.ftl",
     monomorphize => "../locales/en-US/monomorphize.ftl",
     parse => "../locales/en-US/parse.ftl",
     passes => "../locales/en-US/passes.ftl",

compiler/rustc_mir_build/Cargo.toml

@@ -17,6 +17,7 @@ rustc_index = { path = "../rustc_index" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_infer = { path = "../rustc_infer" }
+rustc_macros = { path = "../rustc_macros" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_session = { path = "../rustc_session" }
 rustc_span = { path = "../rustc_span" }

compiler/rustc_mir_build/src/errors.rs

@@ -0,0 +1,13 @@
+use rustc_macros::LintDiagnostic;
+use rustc_span::Span;
+
+#[derive(LintDiagnostic)]
+#[lint(mir_build::unconditional_recursion)]
+#[help]
+pub struct UnconditionalRecursion {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    #[label(mir_build::unconditional_recursion_call_site_label)]
+    pub call_sites: Vec<Span>,
+}

compiler/rustc_mir_build/src/lib.rs

@@ -19,6 +19,7 @@
 
 mod build;
 mod check_unsafety;
+mod errors;
 mod lints;
 pub mod thir;
 

compiler/rustc_mir_build/src/lints.rs

@@ -1,3 +1,4 @@
+use crate::errors::UnconditionalRecursion;
 use rustc_data_structures::graph::iterate::{
     NodeStatus, TriColorDepthFirstSearch, TriColorVisitor,
 };
@@ -36,20 +37,10 @@ pub(crate) fn check<'tcx>(tcx: TyCtxt<'tcx>, body: &Body<'tcx>) {
 
         let sp = tcx.def_span(def_id);
         let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
-        tcx.struct_span_lint_hir(
-            UNCONDITIONAL_RECURSION,
-            hir_id,
-            sp,
-            "function cannot return without recursing",
-            |lint| {
-                lint.span_label(sp, "cannot return without recursing");
-                // offer some help to the programmer.
-                for call_span in vis.reachable_recursive_calls {
-                    lint.span_label(call_span, "recursive call site");
-                }
-                lint.help("a `loop` may express intention better if this is on purpose")
-            },
-        );
+        tcx.emit_spanned_lint(UNCONDITIONAL_RECURSION, hir_id, sp, UnconditionalRecursion {
+            span: sp,
+            call_sites: vis.reachable_recursive_calls,
+        });
     }
 }