Add checks for a block before a unary plus. Fix failing tests

compiler/rustc_parse/src/parser/expr.rs

@@ -165,9 +165,12 @@ impl<'a> Parser<'a> {
             if [token::DotDot, token::DotDotDot, token::DotDotEq].contains(&self.token.kind) {
                 return self.parse_prefix_range_expr(attrs);
             } else {
-                self.parse_prefix_expr(attrs)?
+                let result = self.parse_prefix_expr(attrs);
+                debug!("parse_prefix_expr result: {:?}", &result);
+                result?
             }
         };
+        debug!("parse_assoc_expr_with(lhs = {:?})", &lhs);
         let last_type_ascription_set = self.last_type_ascription.is_some();
 
         if !self.should_continue_as_assoc_expr(&lhs) {
@@ -175,8 +178,11 @@ impl<'a> Parser<'a> {
             return Ok(lhs);
         }
 
+        debug!("continue_as_assoc_expr");
+
         self.expected_tokens.push(TokenType::Operator);
         while let Some(op) = self.check_assoc_op() {
+            debug!("op: {:?}", op);
             // Adjust the span for interpolated LHS to point to the `$lhs` token
             // and not to what it refers to.
             let lhs_span = match self.prev_token.kind {
@@ -520,17 +526,25 @@ impl<'a> Parser<'a> {
                 make_it!(this, attrs, |this, _| this.parse_borrow_expr(lo))
             }
             token::BinOp(token::Plus) => {
-                this.struct_span_err(lo, "leading `+` is not supported")
+                debug!("leading + detected: {:?}", lo);
-                    .span_label(lo, "unexpected `+`")
+                let mut err = this.struct_span_err(lo, "leading `+` is not supported");
-                    .span_suggestion_short(
+                err.span_label(lo, "unexpected `+`");
+
+                // a block on the LHS might have been intended to be an expression instead
+                let sp = this.sess.source_map().start_point(lo);
+                if let Some(sp) = this.sess.ambiguous_block_expr_parse.borrow().get(&sp) {
+                    this.sess.expr_parentheses_needed(&mut err, *sp);
+                } else {
+                   err.span_suggestion(
                         lo,
-                        "remove the `+`",
+                        "try removing the `+`",
                         "".to_string(),
                         Applicability::MachineApplicable,
-                    )
+                    );
-                    .emit();
+                }
-                this.bump();
+                err.emit();
 
+                this.bump();
                 this.parse_prefix_expr(None)
             } // `+expr`
             token::Ident(..) if this.token.is_keyword(kw::Box) => {

compiler/rustc_parse/src/parser/stmt.rs

@@ -21,6 +21,8 @@ use rustc_span::symbol::{kw, sym};
 
 use std::mem;
 
+use tracing::debug;
+
 impl<'a> Parser<'a> {
     /// Parses a statement. This stops just before trailing semicolons on everything but items.
     /// e.g., a `StmtKind::Semi` parses to a `StmtKind::Expr`, leaving the trailing `;` unconsumed.
@@ -418,6 +420,7 @@ impl<'a> Parser<'a> {
             if self.token == token::Eof {
                 break;
             }
+            debug!("parsing statements, stmts: {:?}", &stmts);
             let stmt = match self.parse_full_stmt(recover) {
                 Err(mut err) if recover.yes() => {
                     self.maybe_annotate_with_ascription(&mut err, false);

src/test/ui/associated-types/issue-36499.stderr

@@ -1,8 +1,11 @@
-error: expected expression, found `+`
+error: leading `+` is not supported
   --> $DIR/issue-36499.rs:4:9
    |
 LL |     2 + +2;
-   |         ^ expected expression
+   |         ^
+   |         |
+   |         unexpected `+`
+   |         help: try removing the `+`
 
 error: aborting due to previous error
 

src/test/ui/parser/expr-as-stmt.fixed

@@ -5,18 +5,18 @@
 #![allow(unused_must_use)]
 
 fn foo() -> i32 {
-    ({2}) + {2} //~ ERROR expected expression, found `+`
+    ({2}) + {2} //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
 }
 
 fn bar() -> i32 {
-    ({2}) + 2 //~ ERROR expected expression, found `+`
+    ({2}) + 2 //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
 }
 
 fn zul() -> u32 {
     let foo = 3;
-    ({ 42 }) + foo; //~ ERROR expected expression, found `+`
+    ({ 42 }) + foo; //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
     32
 }

src/test/ui/parser/expr-as-stmt.rs

@@ -5,18 +5,18 @@
 #![allow(unused_must_use)]
 
 fn foo() -> i32 {
-    {2} + {2} //~ ERROR expected expression, found `+`
+    {2} + {2} //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
 }
 
 fn bar() -> i32 {
-    {2} + 2 //~ ERROR expected expression, found `+`
+    {2} + 2 //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
 }
 
 fn zul() -> u32 {
     let foo = 3;
-    { 42 } + foo; //~ ERROR expected expression, found `+`
+    { 42 } + foo; //~ ERROR leading `+` is not supported
     //~^ ERROR mismatched types
     32
 }

src/test/ui/parser/expr-as-stmt.stderr

@@ -1,30 +1,30 @@
-error: expected expression, found `+`
+error: leading `+` is not supported
   --> $DIR/expr-as-stmt.rs:8:9
    |
 LL |     {2} + {2}
-   |         ^ expected expression
+   |         ^ unexpected `+`
    |
 help: parentheses are required to parse this as an expression
    |
 LL |     ({2}) + {2}
    |     +   +
 
-error: expected expression, found `+`
+error: leading `+` is not supported
   --> $DIR/expr-as-stmt.rs:13:9
    |
 LL |     {2} + 2
-   |         ^ expected expression
+   |         ^ unexpected `+`
    |
 help: parentheses are required to parse this as an expression
    |
 LL |     ({2}) + 2
    |     +   +
 
-error: expected expression, found `+`
+error: leading `+` is not supported
   --> $DIR/expr-as-stmt.rs:19:12
    |
 LL |     { 42 } + foo;
-   |            ^ expected expression
+   |            ^ unexpected `+`
    |
 help: parentheses are required to parse this as an expression
    |

src/test/ui/parser/issue-88276-unary-plus.fixed

@@ -3,10 +3,10 @@
 fn main() {
     let _ = 1; //~ ERROR leading `+` is not supported
     let _ = -(1+2)*3; //~ ERROR leading `+` is not supported
-    let _ = -(1+2)*3; //~ ERROR leading `+` is not supported
-                        //~| ERROR leading `+` is not supported
     let _ = --(1+2)*3; //~ ERROR leading `+` is not supported
                          //~| ERROR leading `+` is not supported
+    let _ = (1 + 2) * 3; //~ ERROR leading `+` is not supported
+                           //~| ERROR leading `+` is not supported
     let _ = (&"hello"); //~ ERROR leading `+` is not supported
     let _ = [3, 4+6]; //~ ERROR leading `+` is not supported
                         //~| ERROR leading `+` is not supported

src/test/ui/parser/issue-88276-unary-plus.rs

@@ -3,10 +3,10 @@
 fn main() {
     let _ = +1; //~ ERROR leading `+` is not supported
     let _ = -+(1+2)*3; //~ ERROR leading `+` is not supported
-    let _ = +-+(1+2)*3; //~ ERROR leading `+` is not supported
-                        //~| ERROR leading `+` is not supported
     let _ = -+-+(1+2)*3; //~ ERROR leading `+` is not supported
                          //~| ERROR leading `+` is not supported
+    let _ = (1 + +2) * +3; //~ ERROR leading `+` is not supported
+                           //~| ERROR leading `+` is not supported
     let _ = (+&"hello"); //~ ERROR leading `+` is not supported
     let _ = +[+3, 4+6]; //~ ERROR leading `+` is not supported
                         //~| ERROR leading `+` is not supported

src/test/ui/parser/issue-88276-unary-plus.stderr

@@ -5,7 +5,7 @@ LL |     let _ = +1;
    |             ^
    |             |
    |             unexpected `+`
-   |             help: remove the `+`
+   |             help: try removing the `+`
 
 error: leading `+` is not supported
   --> $DIR/issue-88276-unary-plus.rs:5:14
@@ -14,43 +14,43 @@ LL |     let _ = -+(1+2)*3;
    |              ^
    |              |
    |              unexpected `+`
-   |              help: remove the `+`
+   |              help: try removing the `+`
 
 error: leading `+` is not supported
-  --> $DIR/issue-88276-unary-plus.rs:6:13
+  --> $DIR/issue-88276-unary-plus.rs:6:14
-   |
-LL |     let _ = +-+(1+2)*3;
-   |             ^
-   |             |
-   |             unexpected `+`
-   |             help: remove the `+`
-
-error: leading `+` is not supported
-  --> $DIR/issue-88276-unary-plus.rs:6:15
-   |
-LL |     let _ = +-+(1+2)*3;
-   |               ^
-   |               |
-   |               unexpected `+`
-   |               help: remove the `+`
-
-error: leading `+` is not supported
-  --> $DIR/issue-88276-unary-plus.rs:8:14
    |
 LL |     let _ = -+-+(1+2)*3;
    |              ^
    |              |
    |              unexpected `+`
-   |              help: remove the `+`
+   |              help: try removing the `+`
 
 error: leading `+` is not supported
-  --> $DIR/issue-88276-unary-plus.rs:8:16
+  --> $DIR/issue-88276-unary-plus.rs:6:16
    |
 LL |     let _ = -+-+(1+2)*3;
    |                ^
    |                |
    |                unexpected `+`
-   |                help: remove the `+`
+   |                help: try removing the `+`
+
+error: leading `+` is not supported
+  --> $DIR/issue-88276-unary-plus.rs:8:18
+   |
+LL |     let _ = (1 + +2) * +3;
+   |                  ^
+   |                  |
+   |                  unexpected `+`
+   |                  help: try removing the `+`
+
+error: leading `+` is not supported
+  --> $DIR/issue-88276-unary-plus.rs:8:24
+   |
+LL |     let _ = (1 + +2) * +3;
+   |                        ^
+   |                        |
+   |                        unexpected `+`
+   |                        help: try removing the `+`
 
 error: leading `+` is not supported
   --> $DIR/issue-88276-unary-plus.rs:10:14
@@ -59,7 +59,7 @@ LL |     let _ = (+&"hello");
    |              ^
    |              |
    |              unexpected `+`
-   |              help: remove the `+`
+   |              help: try removing the `+`
 
 error: leading `+` is not supported
   --> $DIR/issue-88276-unary-plus.rs:11:13
@@ -68,7 +68,7 @@ LL |     let _ = +[+3, 4+6];
    |             ^
    |             |
    |             unexpected `+`
-   |             help: remove the `+`
+   |             help: try removing the `+`
 
 error: leading `+` is not supported
   --> $DIR/issue-88276-unary-plus.rs:11:15
@@ -77,7 +77,7 @@ LL |     let _ = +[+3, 4+6];
    |               ^
    |               |
    |               unexpected `+`
-   |               help: remove the `+`
+   |               help: try removing the `+`
 
 error: aborting due to 9 previous errors