Bump MSRV to 1.53

This resolves some lint name problems and provides BTreeMap::retain

Author: rnarubin

.github/workflows/hedwig.yml

@@ -48,14 +48,14 @@ jobs:
           command: doc
           args: --all-features --manifest-path=Cargo.toml
         env:
-          RUSTDOCFLAGS: --cfg docsrs -Dmissing_docs -Dbroken_intra_doc_links
+          RUSTDOCFLAGS: --cfg docsrs -Dmissing_docs -Drustdoc::broken_intra_doc_links
 
   test:
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
-        rust_toolchain: [nightly, stable, 1.49.0]
+        rust_toolchain: [nightly, stable, 1.53.0]
         os: [ubuntu-latest, windows-latest, macOS-latest]
     timeout-minutes: 20
     steps:

src/backends/googlepubsub/mod.rs

@@ -43,14 +43,14 @@ macro_rules! match_fields {
         // nested cfg_attr prevents older compilers from parsing the new doc = EXPR syntax
         #[cfg_attr(docsrs, cfg_attr(docsrs,
             doc = "", // newline
-            doc = concat!("This is a more ergonomic wrapper over [`", match_fields!(@stringify_path $target), "`]")
+            doc = concat!("This is a more ergonomic wrapper over [`", stringify!($target), "`]")
         ))]
         #[cfg_attr(not(docsrs), allow(missing_docs))]
         pub struct $struct_name $(<$struct_generics>)? {
             $(
                 #[cfg_attr(docsrs, cfg_attr(docsrs, doc = concat!(
                     "See [`", stringify!($field_name), "`]",
-                    "(", match_fields!(@stringify_path $target::$field_name), ")"
+                    "(", stringify!($target), "::", stringify!($field_name), ")"
                 )))]
                 $(#[$field_attr])*
                 pub $field_name : $field_type,
@@ -73,13 +73,6 @@ macro_rules! match_fields {
             };
         }
     };
-
-    // directly calling `stringify!` on a path will put spaces inbetween the :: separators, which
-    // then breaks doc linking.
-    // For whatever reason (expansion order maybe?), a macro indirection makes the path space-less
-    (@stringify_path $p:path) => {
-        stringify!($p)
-    };
 }
 
 mod consumer;