Increase accuracy of if condition misparse suggestion

compiler/rustc_parse/src/parser/expr.rs

@@ -2683,6 +2683,13 @@ impl<'a> Parser<'a> {
                 //            ^^
                 //     }
                 //
+                // We account for macro calls that were meant as conditions as well.
+                //
+                //     if ... {
+                //     } else if macro! { foo bar } {
+                //            ^^
+                //     }
+                //
                 // If $cond is "statement-like" such as ExprKind::While then we
                 // want to suggest wrapping in braces.
                 //
@@ -2693,7 +2700,9 @@ impl<'a> Parser<'a> {
                 //     }
                 //     ^
                     if self.check(&TokenKind::OpenDelim(Delimiter::Brace))
-                        && classify::expr_requires_semi_to_be_stmt(&cond) =>
+                        && (classify::expr_requires_semi_to_be_stmt(&cond)
+                            || matches!(cond.kind, ExprKind::MacCall(..)))
+                    =>
                 {
                     self.dcx().emit_err(errors::ExpectedElseBlock {
                         first_tok_span,

compiler/rustc_parse/src/parser/stmt.rs

@@ -475,6 +475,7 @@ impl<'a> Parser<'a> {
     }
 
     fn error_block_no_opening_brace_msg(&mut self, msg: Cow<'static, str>) -> Diag<'a> {
+        let prev = self.prev_token.span;
         let sp = self.token.span;
         let mut e = self.dcx().struct_span_err(sp, msg);
         let do_not_suggest_help = self.token.is_keyword(kw::In) || self.token == token::Colon;
@@ -514,8 +515,97 @@ impl<'a> Parser<'a> {
                 } else {
                     stmt.span
                 };
+                self.suggest_fixes_misparsed_for_loop_head(
+                    &mut e,
+                    prev.between(sp),
+                    stmt_span,
+                    &stmt.kind,
+                );
+            }
+            Err(e) => {
+                self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
+                e.cancel();
+            }
+            _ => {}
+        }
+        e.span_label(sp, "expected `{`");
+        e
+    }
+
+    fn suggest_fixes_misparsed_for_loop_head(
+        &self,
+        e: &mut Diag<'_>,
+        between: Span,
+        stmt_span: Span,
+        stmt_kind: &StmtKind,
+    ) {
+        match (&self.token.kind, &stmt_kind) {
+            (token::OpenDelim(Delimiter::Brace), StmtKind::Expr(expr))
+                if let ExprKind::Call(..) = expr.kind =>
+            {
+                // for _ in x y() {}
+                e.span_suggestion_verbose(
+                    between,
+                    "you might have meant to write a method call",
+                    ".".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            (token::OpenDelim(Delimiter::Brace), StmtKind::Expr(expr))
+                if let ExprKind::Field(..) = expr.kind =>
+            {
+                // for _ in x y.z {}
+                e.span_suggestion_verbose(
+                    between,
+                    "you might have meant to write a field access",
+                    ".".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            (token::CloseDelim(Delimiter::Brace), StmtKind::Expr(expr))
+                if let ExprKind::Struct(expr) = &expr.kind
+                    && let None = expr.qself
+                    && expr.path.segments.len() == 1 =>
+            {
+                // This is specific to "mistyped `if` condition followed by empty body"
+                //
+                // for _ in x y {}
+                e.span_suggestion_verbose(
+                    between,
+                    "you might have meant to write a field access",
+                    ".".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            (token::OpenDelim(Delimiter::Brace), StmtKind::Expr(expr))
+                if let ExprKind::Lit(lit) = expr.kind
+                    && let None = lit.suffix
+                    && let token::LitKind::Integer | token::LitKind::Float = lit.kind =>
+            {
+                // for _ in x 0 {}
+                // for _ in x 0.0 {}
+                e.span_suggestion_verbose(
+                    between,
+                    format!("you might have meant to write a field access"),
+                    ".".to_string(),
+                    Applicability::MaybeIncorrect,
+                );
+            }
+            (token::OpenDelim(Delimiter::Brace), StmtKind::Expr(expr))
+                if let ExprKind::Loop(..)
+                | ExprKind::If(..)
+                | ExprKind::While(..)
+                | ExprKind::Match(..)
+                | ExprKind::ForLoop { .. }
+                | ExprKind::TryBlock(..)
+                | ExprKind::Ret(..)
+                | ExprKind::Closure(..)
+                | ExprKind::Struct(..)
+                | ExprKind::Try(..) = expr.kind =>
+            {
+                // These are more likely to have been meant as a block body.
                 e.multipart_suggestion(
-                    "try placing this code inside a block",
+                    "you might have meant to write this as part of a block",
                     vec![
                         (stmt_span.shrink_to_lo(), "{ ".to_string()),
                         (stmt_span.shrink_to_hi(), " }".to_string()),
@@ -524,14 +614,19 @@ impl<'a> Parser<'a> {
                     Applicability::MaybeIncorrect,
                 );
             }
-            Err(e) => {
-                self.recover_stmt_(SemiColonMode::Break, BlockMode::Ignore);
-                e.cancel();
+            (token::OpenDelim(Delimiter::Brace), _) => {}
+            (_, _) => {
+                e.multipart_suggestion(
+                    "you might have meant to write this as part of a block",
+                    vec![
+                        (stmt_span.shrink_to_lo(), "{ ".to_string()),
+                        (stmt_span.shrink_to_hi(), " }".to_string()),
+                    ],
+                    // Speculative; has been misleading in the past (#46836).
+                    Applicability::MaybeIncorrect,
+                );
             }
-            _ => {}
         }
-        e.span_label(sp, "expected `{`");
-        e
     }
 
     fn error_block_no_opening_brace<T>(&mut self) -> PResult<'a, T> {

tests/ui/issues/issue-39848.stderr

@@ -16,10 +16,10 @@ LL |         if $tgt.has_$field() {}
 LL |     get_opt!(bar, foo);
    |     ------------------ in this macro invocation
    = note: this error originates in the macro `get_opt` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: try placing this code inside a block
+help: you might have meant to write a method call
    |
-LL |         if $tgt.has_{ $field() } {}
-   |                     +          +
+LL |         if $tgt.has_.$field() {}
+   |                     +
 
 error: aborting due to 1 previous error
 

tests/ui/let-else/let-else-if.stderr

@@ -4,7 +4,7 @@ error: conditional `else if` is not supported for `let...else`
 LL |     let Some(_) = Some(()) else if true {
    |                                 ^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL ~     let Some(_) = Some(()) else { if true {
 LL |

tests/ui/lint/issue-104392.stderr

@@ -6,7 +6,7 @@ LL |     { unsafe 92 }
    |       |
    |       while parsing this `unsafe` expression
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     { unsafe { 92 } }
    |              +    +

tests/ui/missing/missing-block-hint.stderr

@@ -25,7 +25,7 @@ note: the `if` expression is missing a block after this condition
    |
 LL |         if (foo)
    |            ^^^^^
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |             { bar; }
    |             +      +

tests/ui/parser/bad-if-statements.stderr

@@ -29,7 +29,7 @@ note: the `if` expression is missing a block after this condition
    |
 LL |     if true x
    |        ^^^^
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     if true { x }
    |             +   +
@@ -65,7 +65,7 @@ note: the `if` expression is missing a block after this condition
    |
 LL |     if true x else {}
    |        ^^^^
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     if true { x } else {}
    |             +   +

tests/ui/parser/block-no-opening-brace.stderr

@@ -6,7 +6,7 @@ LL |     loop
 LL |         let x = 0;
    |         ^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |         { let x = 0; }
    |         +            +
@@ -21,7 +21,7 @@ LL |     while true
 LL |         let x = 0;
    |         ^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |         { let x = 0; }
    |         +            +
@@ -32,7 +32,7 @@ error: expected `{`, found keyword `let`
 LL |         let x = 0;
    |         ^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |         { let x = 0; }
    |         +            +

tests/ui/parser/closure-return-syntax.stderr

@@ -4,7 +4,7 @@ error: expected `{`, found `22`
 LL |     let x = || -> i32 22;
    |                       ^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     let x = || -> i32 { 22 };
    |                       +    +

tests/ui/parser/else-no-if.stderr

@@ -30,7 +30,7 @@ error: expected `{`, found `falsy`
 LL |     } else falsy();
    |            ^^^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     } else { falsy() };
    |            +         +
@@ -41,7 +41,7 @@ error: expected `{`, found keyword `loop`
 LL |     } else loop{}
    |            ^^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     } else { loop{} }
    |            +        +
@@ -65,7 +65,7 @@ error: expected `{`, found `falsy`
 LL |     } else falsy!();
    |            ^^^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     } else { falsy!() };
    |            +          +
@@ -74,20 +74,22 @@ error: expected `{`, found `falsy`
   --> $DIR/else-no-if.rs:47:12
    |
 LL |     } else falsy! {} {
-   |            ^^^^^ expected `{`
+   |       ---- ^^^^^
+   |       |
+   |       expected an `if` or a block after this `else`
    |
-help: try placing this code inside a block
+help: add an `if` if this is the condition of a chained `else if` statement
    |
-LL |     } else { falsy! {} } {
-   |            +           +
+LL |     } else if falsy! {} {
+   |            ++
 
 error: expected `{`, found `falsy`
   --> $DIR/else-no-if.rs:54:12
    |
 LL |     } else falsy! {};
    |            ^^^^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     } else { falsy! {} };
    |            +           +

tests/ui/parser/label-after-block-like.stderr

@@ -23,7 +23,7 @@ note: the `if` expression is missing a block after this condition
    |
 LL |     if let () = () 'a {}
    |        ^^^^^^^^^^^
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     if let () = () { 'a {} }
    |                    +       +
@@ -53,7 +53,7 @@ note: the `if` expression is missing a block after this condition
    |
 LL |     if true 'a {}
    |        ^^^^
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     if true { 'a {} }
    |             +       +
@@ -80,7 +80,7 @@ LL |     loop 'a {}
    |     |
    |     while parsing this `loop` expression
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     loop { 'a {} }
    |          +       +
@@ -108,7 +108,7 @@ LL |     while true 'a {}
    |     |     this `while` condition successfully parsed
    |     while parsing the body of this `while` expression
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     while true { 'a {} }
    |                +       +
@@ -136,7 +136,7 @@ LL |     while let () = () 'a {}
    |     |     this `while` condition successfully parsed
    |     while parsing the body of this `while` expression
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     while let () = () { 'a {} }
    |                       +       +
@@ -161,7 +161,7 @@ error: expected `{`, found `'a`
 LL |     for _ in 0..0 'a {}
    |                   ^^ expected `{`
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     for _ in 0..0 { 'a {} }
    |                   +       +
@@ -188,7 +188,7 @@ LL |     unsafe 'a {}
    |     |
    |     while parsing this `unsafe` expression
    |
-help: try placing this code inside a block
+help: you might have meant to write this as part of a block
    |
 LL |     unsafe { 'a {} }
    |            +       +