From ddb225f1f57882c4f87d99d585fab982461d1fd9 Mon Sep 17 00:00:00 2001
From: yukang <moorekang@gmail.com>
Date: Wed, 7 Sep 2022 12:26:50 +0800
Subject: [PATCH] fixes #101477: Recover from typo where == is used in place of
 =

---
 .../locales/en-US/parser.ftl                     |  3 +++
 compiler/rustc_parse/src/parser/diagnostics.rs   | 16 ++++++++++++++++
 src/test/ui/parser/issue-101477-enum.fixed       | 10 ++++++++++
 src/test/ui/parser/issue-101477-enum.rs          | 10 ++++++++++
 src/test/ui/parser/issue-101477-enum.stderr      | 14 ++++++++++++++
 src/test/ui/parser/issue-101477-let.fixed        |  6 ++++++
 src/test/ui/parser/issue-101477-let.rs           |  6 ++++++
 src/test/ui/parser/issue-101477-let.stderr       |  8 ++++++++
 8 files changed, 73 insertions(+)
 create mode 100644 src/test/ui/parser/issue-101477-enum.fixed
 create mode 100644 src/test/ui/parser/issue-101477-enum.rs
 create mode 100644 src/test/ui/parser/issue-101477-enum.stderr
 create mode 100644 src/test/ui/parser/issue-101477-let.fixed
 create mode 100644 src/test/ui/parser/issue-101477-let.rs
 create mode 100644 src/test/ui/parser/issue-101477-let.stderr

diff --git a/compiler/rustc_error_messages/locales/en-US/parser.ftl b/compiler/rustc_error_messages/locales/en-US/parser.ftl
index bc17754c56ae3..f74df3d9746ae 100644
--- a/compiler/rustc_error_messages/locales/en-US/parser.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/parser.ftl
@@ -153,3 +153,6 @@ parser_left_arrow_operator = unexpected token: `<-`
 
 parser_remove_let = expected pattern, found `let`
     .suggestion = remove the unnecessary `let` keyword
+
+parser_use_eq_instead = unexpected `==`
+    .suggestion = try using `=` instead
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index ad49227222b2c..be524db785bc0 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -713,6 +713,14 @@ pub(crate) struct RemoveLet {
     pub span: Span,
 }
 
+#[derive(SessionDiagnostic)]
+#[diag(parser::use_eq_instead)]
+pub(crate) struct UseEqInstead {
+    #[primary_span]
+    #[suggestion_short(applicability = "machine-applicable", code = "=")]
+    pub span: Span,
+}
+
 // SnapshotParser is used to create a snapshot of the parser
 // without causing duplicate errors being emitted when the `Parser`
 // is dropped.
@@ -957,6 +965,14 @@ impl<'a> Parser<'a> {
             }
         }
 
+        if self.token.kind == TokenKind::EqEq
+            && self.prev_token.is_ident()
+            && expected.iter().any(|tok| matches!(tok, TokenType::Token(TokenKind::Eq)))
+        {
+            // Likely typo: `=` → `==` in let expr or enum item
+            return Err(self.sess.create_err(UseEqInstead { span: self.token.span }));
+        }
+
         let expect = tokens_to_string(&expected);
         let actual = super::token_descr(&self.token);
         let (msg_exp, (label_sp, label_exp)) = if expected.len() > 1 {
diff --git a/src/test/ui/parser/issue-101477-enum.fixed b/src/test/ui/parser/issue-101477-enum.fixed
new file mode 100644
index 0000000000000..1dfeae22aea2f
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.fixed
@@ -0,0 +1,10 @@
+// run-rustfix
+
+#[allow(dead_code)]
+enum Demo {
+    A = 1,
+    B = 2 //~ ERROR unexpected `==`
+    //~^ expected item, found `==`
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-101477-enum.rs b/src/test/ui/parser/issue-101477-enum.rs
new file mode 100644
index 0000000000000..ea7051d69a4c7
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.rs
@@ -0,0 +1,10 @@
+// run-rustfix
+
+#[allow(dead_code)]
+enum Demo {
+    A = 1,
+    B == 2 //~ ERROR unexpected `==`
+    //~^ expected item, found `==`
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-101477-enum.stderr b/src/test/ui/parser/issue-101477-enum.stderr
new file mode 100644
index 0000000000000..bffc881bdc84b
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-enum.stderr
@@ -0,0 +1,14 @@
+error: unexpected `==`
+  --> $DIR/issue-101477-enum.rs:6:7
+   |
+LL |     B == 2
+   |       ^^ help: try using `=` instead
+
+error: expected item, found `==`
+  --> $DIR/issue-101477-enum.rs:6:7
+   |
+LL |     B == 2
+   |       ^^ expected item
+
+error: aborting due to 2 previous errors
+
diff --git a/src/test/ui/parser/issue-101477-let.fixed b/src/test/ui/parser/issue-101477-let.fixed
new file mode 100644
index 0000000000000..9989ad81524e1
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.fixed
@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let x = 2; //~ ERROR unexpected `==`
+    println!("x: {}", x)
+}
diff --git a/src/test/ui/parser/issue-101477-let.rs b/src/test/ui/parser/issue-101477-let.rs
new file mode 100644
index 0000000000000..8b0e8bee1799d
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.rs
@@ -0,0 +1,6 @@
+// run-rustfix
+
+fn main() {
+    let x == 2; //~ ERROR unexpected `==`
+    println!("x: {}", x)
+}
diff --git a/src/test/ui/parser/issue-101477-let.stderr b/src/test/ui/parser/issue-101477-let.stderr
new file mode 100644
index 0000000000000..1b30d4b17861a
--- /dev/null
+++ b/src/test/ui/parser/issue-101477-let.stderr
@@ -0,0 +1,8 @@
+error: unexpected `==`
+  --> $DIR/issue-101477-let.rs:4:11
+   |
+LL |     let x == 2;
+   |           ^^ help: try using `=` instead
+
+error: aborting due to previous error
+