Detect missing `.` in method chain in let bindings and statements

On parse errors where an ident is found where one wasn't expected, see if the next elements might have been meant as method call or field access.

```
error: expected one of `.`, `;`, `?`, `else`, or an operator, found `map`
  --> $DIR/missing-dot-on-statement-expression.rs:7:29
   |
LL |     let _ = [1, 2, 3].iter()map(|x| x);
   |                             ^^^ expected one of `.`, `;`, `?`, `else`, or an operator
   |
help: you might have meant to write a method call
   |
LL |     let _ = [1, 2, 3].iter().map(|x| x);
   |                             +
```

7 files changed, 165 insertions, 2 deletions

diff --git a/compiler/rustc_parse/src/parser/stmt.rs b/compiler/rustc_parse/src/parser/stmt.rs
index 151abf0be95..259bc3dcd36 100644
--- a/compiler/rustc_parse/src/parser/stmt.rs
+++ b/compiler/rustc_parse/src/parser/stmt.rs
@@ -745,6 +745,42 @@ impl<'a> Parser<'a> {
         Ok(self.mk_block(stmts, s, lo.to(self.prev_token.span)))
     }
 
+    fn recover_missing_dot(&mut self, err: &mut Diag<'_>) {
+        if !self.token.is_ident() {
+            return;
+        }
+        if self.token.is_reserved_ident() && !self.token.is_ident_named(kw::Await) {
+            return;
+        }
+        if self.prev_token.is_reserved_ident() && self.prev_token.is_ident_named(kw::Await) {
+            // Likely `foo.await bar`
+        } else if !self.prev_token.is_reserved_ident() && self.prev_token.is_ident() {
+            // Likely `foo bar`
+        } else if self.prev_token.kind == token::Question {
+            // `foo? bar`
+        } else if self.prev_token.kind == token::CloseDelim(Delimiter::Parenthesis) {
+            // `foo() bar`
+        } else {
+            return;
+        }
+        if self.look_ahead(1, |t| [token::Semi, token::Question, token::Dot].contains(&t.kind)) {
+            err.span_suggestion_verbose(
+                self.prev_token.span.between(self.token.span),
+                "you might have meant to write a field access",
+                ".".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+        if self.look_ahead(1, |t| t.kind == token::OpenDelim(Delimiter::Parenthesis)) {
+            err.span_suggestion_verbose(
+                self.prev_token.span.between(self.token.span),
+                "you might have meant to write a method call",
+                ".".to_string(),
+                Applicability::MaybeIncorrect,
+            );
+        }
+    }
+
     /// Parses a statement, including the trailing semicolon.
     pub fn parse_full_stmt(
         &mut self,
@@ -851,7 +887,8 @@ impl<'a> Parser<'a> {
                             Some(if recover.no() {
                                 res?
                             } else {
-                                res.unwrap_or_else(|e| {
+                                res.unwrap_or_else(|mut e| {
+                                    self.recover_missing_dot(&mut e);
                                     let guar = e.emit();
                                     self.recover_stmt();
                                     guar
@@ -872,7 +909,12 @@ impl<'a> Parser<'a> {
                 // We might be at the `,` in `let x = foo<bar, baz>;`. Try to recover.
                 match &mut local.kind {
                     LocalKind::Init(expr) | LocalKind::InitElse(expr, _) => {
-                        self.check_mistyped_turbofish_with_multiple_type_params(e, expr)?;
+                        self.check_mistyped_turbofish_with_multiple_type_params(e, expr).map_err(
+                            |mut e| {
+                                self.recover_missing_dot(&mut e);
+                                e
+                            },
+                        )?;
                         // We found `foo<bar, baz>`, have we fully recovered?
                         self.expect_semi()?;
                     }
diff --git a/tests/ui/parser/raw/raw-literal-keywords.stderr b/tests/ui/parser/raw/raw-literal-keywords.stderr
index f7b6c894a90..c7d63672661 100644
--- a/tests/ui/parser/raw/raw-literal-keywords.stderr
+++ b/tests/ui/parser/raw/raw-literal-keywords.stderr
@@ -9,12 +9,22 @@ error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found
    |
 LL |     r#struct Test;
    |              ^^^^ expected one of 8 possible tokens
+   |
+help: you might have meant to write a field access
+   |
+LL |     r#struct.Test;
+   |             +
 
 error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `Test`
   --> $DIR/raw-literal-keywords.rs:10:13
    |
 LL |     r#union Test;
    |             ^^^^ expected one of 8 possible tokens
+   |
+help: you might have meant to write a field access
+   |
+LL |     r#union.Test;
+   |            +
 
 error[E0425]: cannot find value `r#if` in this scope
   --> $DIR/raw-literal-keywords.rs:14:13
diff --git a/tests/ui/parser/recover/missing-dot-on-statement-expression.fixed b/tests/ui/parser/recover/missing-dot-on-statement-expression.fixed
new file mode 100644
index 00000000000..1be4485b474
--- /dev/null
+++ b/tests/ui/parser/recover/missing-dot-on-statement-expression.fixed
@@ -0,0 +1,28 @@
+//@ run-rustfix
+#![allow(unused_must_use, dead_code)]
+struct S {
+    field: (),
+}
+fn main() {
+    let _ = [1, 2, 3].iter().map(|x| x); //~ ERROR expected one of `.`, `;`, `?`, `else`, or an operator, found `map`
+    //~^ HELP you might have meant to write a method call
+}
+fn foo() {
+    let baz = S {
+        field: ()
+    };
+    let _ = baz.field; //~ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `else`, `{`, or an operator, found `field`
+    //~^ HELP you might have meant to write a field
+}
+
+fn bar() {
+    [1, 2, 3].iter().map(|x| x); //~ ERROR expected one of `.`, `;`, `?`, `}`, or an operator, found `map`
+    //~^ HELP you might have meant to write a method call
+}
+fn baz() {
+    let baz = S {
+        field: ()
+    };
+    baz.field; //~ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `field`
+    //~^ HELP you might have meant to write a field
+}
diff --git a/tests/ui/parser/recover/missing-dot-on-statement-expression.rs b/tests/ui/parser/recover/missing-dot-on-statement-expression.rs
new file mode 100644
index 00000000000..5e2b545f414
--- /dev/null
+++ b/tests/ui/parser/recover/missing-dot-on-statement-expression.rs
@@ -0,0 +1,28 @@
+//@ run-rustfix
+#![allow(unused_must_use, dead_code)]
+struct S {
+    field: (),
+}
+fn main() {
+    let _ = [1, 2, 3].iter()map(|x| x); //~ ERROR expected one of `.`, `;`, `?`, `else`, or an operator, found `map`
+    //~^ HELP you might have meant to write a method call
+}
+fn foo() {
+    let baz = S {
+        field: ()
+    };
+    let _ = baz field; //~ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `else`, `{`, or an operator, found `field`
+    //~^ HELP you might have meant to write a field
+}
+
+fn bar() {
+    [1, 2, 3].iter()map(|x| x); //~ ERROR expected one of `.`, `;`, `?`, `}`, or an operator, found `map`
+    //~^ HELP you might have meant to write a method call
+}
+fn baz() {
+    let baz = S {
+        field: ()
+    };
+    baz field; //~ ERROR expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `field`
+    //~^ HELP you might have meant to write a field
+}
diff --git a/tests/ui/parser/recover/missing-dot-on-statement-expression.stderr b/tests/ui/parser/recover/missing-dot-on-statement-expression.stderr
new file mode 100644
index 00000000000..a04d8bd34e2
--- /dev/null
+++ b/tests/ui/parser/recover/missing-dot-on-statement-expression.stderr
@@ -0,0 +1,46 @@
+error: expected one of `.`, `;`, `?`, `else`, or an operator, found `map`
+  --> $DIR/missing-dot-on-statement-expression.rs:7:29
+   |
+LL |     let _ = [1, 2, 3].iter()map(|x| x);
+   |                             ^^^ expected one of `.`, `;`, `?`, `else`, or an operator
+   |
+help: you might have meant to write a method call
+   |
+LL |     let _ = [1, 2, 3].iter().map(|x| x);
+   |                             +
+
+error: expected one of `!`, `.`, `::`, `;`, `?`, `else`, `{`, or an operator, found `field`
+  --> $DIR/missing-dot-on-statement-expression.rs:14:17
+   |
+LL |     let _ = baz field;
+   |                 ^^^^^ expected one of 8 possible tokens
+   |
+help: you might have meant to write a field access
+   |
+LL |     let _ = baz.field;
+   |                +
+
+error: expected one of `.`, `;`, `?`, `}`, or an operator, found `map`
+  --> $DIR/missing-dot-on-statement-expression.rs:19:21
+   |
+LL |     [1, 2, 3].iter()map(|x| x);
+   |                     ^^^ expected one of `.`, `;`, `?`, `}`, or an operator
+   |
+help: you might have meant to write a method call
+   |
+LL |     [1, 2, 3].iter().map(|x| x);
+   |                     +
+
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `field`
+  --> $DIR/missing-dot-on-statement-expression.rs:26:9
+   |
+LL |     baz field;
+   |         ^^^^^ expected one of 8 possible tokens
+   |
+help: you might have meant to write a field access
+   |
+LL |     baz.field;
+   |        +
+
+error: aborting due to 4 previous errors
+
diff --git a/tests/ui/proc-macro/raw-ident.stderr b/tests/ui/proc-macro/raw-ident.stderr
index a72067021cb..32b36c6d989 100644
--- a/tests/ui/proc-macro/raw-ident.stderr
+++ b/tests/ui/proc-macro/raw-ident.stderr
@@ -5,6 +5,10 @@ LL |     make_bad_struct!(S);
    |     ^^^^^^^^^^^^^^^^^^^ expected one of 8 possible tokens
    |
    = note: this error originates in the macro `make_bad_struct` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: you might have meant to write a field access
+   |
+LL |     .;
+   |     ~
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/suggestions/type-ascription-and-other-error.stderr b/tests/ui/suggestions/type-ascription-and-other-error.stderr
index 4efddca4b47..7f8b8b7470e 100644
--- a/tests/ui/suggestions/type-ascription-and-other-error.stderr
+++ b/tests/ui/suggestions/type-ascription-and-other-error.stderr
@@ -3,6 +3,11 @@ error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found
    |
 LL |     not rust;
    |         ^^^^ expected one of 8 possible tokens
+   |
+help: you might have meant to write a field access
+   |
+LL |     not.rust;
+   |        +
 
 error: aborting due to 1 previous error