Rollup merge of #100667 - Xiretza:diag-structs-parser-ivd, r=davidtwco

Migrate "invalid variable declaration" errors to SessionDiagnostic

After seeing the great blog post on Inside Rust, I decided to try my hand at this. Just one diagnostic for now to get used to the workflow and to check if this is the way to do it or if there are any problems.

2 files changed, 41 insertions, 19 deletions

diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 93e70e9abda..eeedfd157be 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -334,6 +334,35 @@ struct InInTypo {
     sugg_span: Span,
 }
 
+#[derive(SessionDiagnostic)]
+#[error(parser::invalid_variable_declaration)]
+pub struct InvalidVariableDeclaration {
+    #[primary_span]
+    pub span: Span,
+    #[subdiagnostic]
+    pub sub: InvalidVariableDeclarationSub,
+}
+
+#[derive(SessionSubdiagnostic)]
+pub enum InvalidVariableDeclarationSub {
+    #[suggestion(
+        parser::switch_mut_let_order,
+        applicability = "maybe-incorrect",
+        code = "let mut"
+    )]
+    SwitchMutLetOrder(#[primary_span] Span),
+    #[suggestion(
+        parser::missing_let_before_mut,
+        applicability = "machine-applicable",
+        code = "let mut"
+    )]
+    MissingLet(#[primary_span] Span),
+    #[suggestion(parser::use_let_not_auto, applicability = "machine-applicable", code = "let")]
+    UseLetNotAuto(#[primary_span] Span),
+    #[suggestion(parser::use_let_not_var, applicability = "machine-applicable", code = "let")]
+    UseLetNotVar(#[primary_span] Span),
+}
+
 // SnapshotParser is used to create a snapshot of the parser
 // without causing duplicate errors being emitted when the `Parser`
 // is dropped.
diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index cac39f8f25f..875636bdc28 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -1,5 +1,7 @@
 use super::attr::DEFAULT_INNER_ATTR_FORBIDDEN;
-use super::diagnostics::{AttemptLocalParseRecovery, Error};
+use super::diagnostics::{
+    AttemptLocalParseRecovery, Error, InvalidVariableDeclaration, InvalidVariableDeclarationSub,
+};
 use super::expr::LhsExpr;
 use super::pat::RecoverComma;
 use super::path::PathStyle;
@@ -58,28 +60,22 @@ impl<'a> Parser<'a> {
         if self.token.is_keyword(kw::Mut) && self.is_keyword_ahead(1, &[kw::Let]) {
             self.bump();
             let mut_let_span = lo.to(self.token.span);
-            self.struct_span_err(mut_let_span, "invalid variable declaration")
-                .span_suggestion(
-                    mut_let_span,
-                    "switch the order of `mut` and `let`",
-                    "let mut",
-                    Applicability::MaybeIncorrect,
-                )
-                .emit();
+            self.sess.emit_err(InvalidVariableDeclaration {
+                span: mut_let_span,
+                sub: InvalidVariableDeclarationSub::SwitchMutLetOrder(mut_let_span),
+            });
         }
 
         Ok(Some(if self.token.is_keyword(kw::Let) {
             self.parse_local_mk(lo, attrs, capture_semi, force_collect)?
         } else if self.is_kw_followed_by_ident(kw::Mut) {
-            self.recover_stmt_local(lo, attrs, "missing keyword", "let mut")?
+            self.recover_stmt_local(lo, attrs, InvalidVariableDeclarationSub::MissingLet)?
         } else if self.is_kw_followed_by_ident(kw::Auto) {
             self.bump(); // `auto`
-            let msg = "write `let` instead of `auto` to introduce a new variable";
-            self.recover_stmt_local(lo, attrs, msg, "let")?
+            self.recover_stmt_local(lo, attrs, InvalidVariableDeclarationSub::UseLetNotAuto)?
         } else if self.is_kw_followed_by_ident(sym::var) {
             self.bump(); // `var`
-            let msg = "write `let` instead of `var` to introduce a new variable";
-            self.recover_stmt_local(lo, attrs, msg, "let")?
+            self.recover_stmt_local(lo, attrs, InvalidVariableDeclarationSub::UseLetNotVar)?
         } else if self.check_path() && !self.token.is_qpath_start() && !self.is_path_start_item() {
             // We have avoided contextual keywords like `union`, items with `crate` visibility,
             // or `auto trait` items. We aim to parse an arbitrary path `a::b` but not something
@@ -217,13 +213,10 @@ impl<'a> Parser<'a> {
         &mut self,
         lo: Span,
         attrs: AttrWrapper,
-        msg: &str,
-        sugg: &str,
+        subdiagnostic: fn(Span) -> InvalidVariableDeclarationSub,
     ) -> PResult<'a, Stmt> {
         let stmt = self.recover_local_after_let(lo, attrs)?;
-        self.struct_span_err(lo, "invalid variable declaration")
-            .span_suggestion(lo, msg, sugg, Applicability::MachineApplicable)
-            .emit();
+        self.sess.emit_err(InvalidVariableDeclaration { span: lo, sub: subdiagnostic(lo) });
         Ok(stmt)
     }