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Rollup merge of rust-lang#62928 - Centril:recover-parens-around-for-h…
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…ead, r=estebank

Syntax: Recover on `for ( $pat in $expr ) $block`

Fixes rust-lang#62724 by adding some recovery:

```
error: unexpected closing `)`
  --> $DIR/recover-for-loop-parens-around-head.rs:10:23
   |
LL |     for ( elem in vec ) {
   |         --------------^
   |         |
   |         opening `(`
   |         help: remove parenthesis in `for` loop: `elem in vec`
```

The last 2 commits are drive-by cleanups.

r? @estebank
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@Centril
Centril authored Jul 30, 2019
2 parents d436b66 + 56b39fb commit 022f7a7
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Showing 4 changed files with 259 additions and 162 deletions.
118 changes: 81 additions & 37 deletions src/libsyntax/parse/diagnostics.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ use crate::ThinVec;
use crate::util::parser::AssocOp;
use errors::{Applicability, DiagnosticBuilder, DiagnosticId};
use rustc_data_structures::fx::FxHashSet;
use syntax_pos::{Span, DUMMY_SP, MultiSpan};
use syntax_pos::{Span, DUMMY_SP, MultiSpan, SpanSnippetError};
use log::{debug, trace};
use std::mem;

Expand Down Expand Up @@ -199,6 +199,10 @@ impl<'a> Parser<'a> {
&self.sess.span_diagnostic
}

crate fn span_to_snippet(&self, span: Span) -> Result<String, SpanSnippetError> {
self.sess.source_map().span_to_snippet(span)
}

crate fn expected_ident_found(&self) -> DiagnosticBuilder<'a> {
let mut err = self.struct_span_err(
self.token.span,
Expand Down Expand Up @@ -549,8 +553,10 @@ impl<'a> Parser<'a> {
ExprKind::Binary(op, _, _) if op.node.is_comparison() => {
// respan to include both operators
let op_span = op.span.to(self.token.span);
let mut err = self.diagnostic().struct_span_err(op_span,
"chained comparison operators require parentheses");
let mut err = self.struct_span_err(
op_span,
"chained comparison operators require parentheses",
);
if op.node == BinOpKind::Lt &&
*outer_op == AssocOp::Less || // Include `<` to provide this recommendation
*outer_op == AssocOp::Greater // even in a case like the following:
Expand Down Expand Up @@ -717,8 +723,6 @@ impl<'a> Parser<'a> {
path.span = ty_span.to(self.prev_span);

let ty_str = self
.sess
.source_map()
.span_to_snippet(ty_span)
.unwrap_or_else(|_| pprust::ty_to_string(&ty));
self.diagnostic()
Expand Down Expand Up @@ -889,7 +893,7 @@ impl<'a> Parser<'a> {
err.span_label(await_sp, "while parsing this incorrect await expression");
err
})?;
let expr_str = self.sess.source_map().span_to_snippet(expr.span)
let expr_str = self.span_to_snippet(expr.span)
.unwrap_or_else(|_| pprust::expr_to_string(&expr));
let suggestion = format!("{}.await{}", expr_str, if is_question { "?" } else { "" });
let sp = lo.to(expr.span);
Expand Down Expand Up @@ -923,6 +927,48 @@ impl<'a> Parser<'a> {
}
}

/// Recover a situation like `for ( $pat in $expr )`
/// and suggest writing `for $pat in $expr` instead.
///
/// This should be called before parsing the `$block`.
crate fn recover_parens_around_for_head(
&mut self,
pat: P<Pat>,
expr: &Expr,
begin_paren: Option<Span>,
) -> P<Pat> {
match (&self.token.kind, begin_paren) {
(token::CloseDelim(token::Paren), Some(begin_par_sp)) => {
self.bump();

let pat_str = self
// Remove the `(` from the span of the pattern:
.span_to_snippet(pat.span.trim_start(begin_par_sp).unwrap())
.unwrap_or_else(|_| pprust::pat_to_string(&pat));

self.struct_span_err(self.prev_span, "unexpected closing `)`")
.span_label(begin_par_sp, "opening `(`")
.span_suggestion(
begin_par_sp.to(self.prev_span),
"remove parenthesis in `for` loop",
format!("{} in {}", pat_str, pprust::expr_to_string(&expr)),
// With e.g. `for (x) in y)` this would replace `(x) in y)`
// with `x) in y)` which is syntactically invalid.
// However, this is prevented before we get here.
Applicability::MachineApplicable,
)
.emit();

// Unwrap `(pat)` into `pat` to avoid the `unused_parens` lint.
pat.and_then(|pat| match pat.node {
PatKind::Paren(pat) => pat,
_ => P(pat),
})
}
_ => pat,
}
}

crate fn could_ascription_be_path(&self, node: &ast::ExprKind) -> bool {
self.token.is_ident() &&
if let ast::ExprKind::Path(..) = node { true } else { false } &&
Expand Down Expand Up @@ -1105,17 +1151,14 @@ impl<'a> Parser<'a> {
crate fn check_for_for_in_in_typo(&mut self, in_span: Span) {
if self.eat_keyword(kw::In) {
// a common typo: `for _ in in bar {}`
let mut err = self.sess.span_diagnostic.struct_span_err(
self.prev_span,
"expected iterable, found keyword `in`",
);
err.span_suggestion_short(
in_span.until(self.prev_span),
"remove the duplicated `in`",
String::new(),
Applicability::MachineApplicable,
);
err.emit();
self.struct_span_err(self.prev_span, "expected iterable, found keyword `in`")
.span_suggestion_short(
in_span.until(self.prev_span),
"remove the duplicated `in`",
String::new(),
Applicability::MachineApplicable,
)
.emit();
}
}

Expand All @@ -1128,12 +1171,12 @@ impl<'a> Parser<'a> {

crate fn eat_incorrect_doc_comment_for_arg_type(&mut self) {
if let token::DocComment(_) = self.token.kind {
let mut err = self.diagnostic().struct_span_err(
self.struct_span_err(
self.token.span,
"documentation comments cannot be applied to a function parameter's type",
);
err.span_label(self.token.span, "doc comments are not allowed here");
err.emit();
)
.span_label(self.token.span, "doc comments are not allowed here")
.emit();
self.bump();
} else if self.token == token::Pound && self.look_ahead(1, |t| {
*t == token::OpenDelim(token::Bracket)
Expand All @@ -1145,12 +1188,12 @@ impl<'a> Parser<'a> {
}
let sp = lo.to(self.token.span);
self.bump();
let mut err = self.diagnostic().struct_span_err(
self.struct_span_err(
sp,
"attributes cannot be applied to a function parameter's type",
);
err.span_label(sp, "attributes are not allowed here");
err.emit();
)
.span_label(sp, "attributes are not allowed here")
.emit();
}
}

Expand Down Expand Up @@ -1206,18 +1249,19 @@ impl<'a> Parser<'a> {
self.expect(&token::Colon)?;
let ty = self.parse_ty()?;

let mut err = self.diagnostic().struct_span_err_with_code(
pat.span,
"patterns aren't allowed in methods without bodies",
DiagnosticId::Error("E0642".into()),
);
err.span_suggestion_short(
pat.span,
"give this argument a name or use an underscore to ignore it",
"_".to_owned(),
Applicability::MachineApplicable,
);
err.emit();
self.diagnostic()
.struct_span_err_with_code(
pat.span,
"patterns aren't allowed in methods without bodies",
DiagnosticId::Error("E0642".into()),
)
.span_suggestion_short(
pat.span,
"give this argument a name or use an underscore to ignore it",
"_".to_owned(),
Applicability::MachineApplicable,
)
.emit();

// Pretend the pattern is `_`, to avoid duplicate errors from AST validation.
let pat = P(Pat {
Expand Down
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