macros: introduce `build_field_mapping`

Move the logic for building a field mapping (which is used by the
building of format strings in `suggestion` annotations) into a helper
function.

Signed-off-by: David Wood <david.wood@huawei.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/compiler/rustc_macros/src/diagnostics/utils.rs b/compiler/rustc_macros/src/diagnostics/utils.rs
index 636bcf1f7b1..24204556c98 100644
--- a/compiler/rustc_macros/src/diagnostics/utils.rs
+++ b/compiler/rustc_macros/src/diagnostics/utils.rs
@@ -2,10 +2,10 @@ use crate::diagnostics::error::{span_err, throw_span_err, SessionDiagnosticDeriv
 use proc_macro::Span;
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote, ToTokens};
-use std::collections::BTreeSet;
+use std::collections::{BTreeSet, HashMap};
 use std::str::FromStr;
 use syn::{spanned::Spanned, Attribute, Meta, Type, TypeTuple};
-use synstructure::BindingInfo;
+use synstructure::{BindingInfo, Structure};
 
 /// Checks whether the type name of `ty` matches `name`.
 ///
@@ -325,3 +325,20 @@ impl quote::ToTokens for Applicability {
         });
     }
 }
+
+/// Build the mapping of field names to fields. This allows attributes to peek values from
+/// other fields.
+pub(crate) fn build_field_mapping<'a>(structure: &Structure<'a>) -> HashMap<String, TokenStream> {
+    let mut fields_map = HashMap::new();
+
+    let ast = structure.ast();
+    if let syn::Data::Struct(syn::DataStruct { fields, .. }) = &ast.data {
+        for field in fields.iter() {
+            if let Some(ident) = &field.ident {
+                fields_map.insert(ident.to_string(), quote! { &self.#ident });
+            }
+        }
+    }
+
+    fields_map
+}