Auto merge of #53854 - davidtwco:issue-53668, r=nikomatsakis

if- and while-let-chains, take 2 - edition changes

Part of #53668.

r? @nikomatsakis

5 files changed, 261 insertions, 0 deletions

diff --git a/src/librustc_passes/ast_validation.rs b/src/librustc_passes/ast_validation.rs
index bca119660aa..52d61792ed2 100644
--- a/src/librustc_passes/ast_validation.rs
+++ b/src/librustc_passes/ast_validation.rs
@@ -22,6 +22,7 @@ use syntax::ast::*;
 use syntax::attr;
 use syntax::source_map::Spanned;
 use syntax::symbol::keywords;
+use syntax::ptr::P;
 use syntax::visit::{self, Visitor};
 use syntax_pos::Span;
 use errors;
@@ -167,11 +168,61 @@ impl<'a> AstValidator<'a> {
                 "only lifetime parameters can be used in this context");
         }
     }
+
+    /// With eRFC 2497, we need to check whether an expression is ambigious and warn or error
+    /// depending on the edition, this function handles that.
+    fn while_if_let_ambiguity(&self, expr: &P<Expr>) {
+        if let Some((span, op_kind)) = self.while_if_let_expr_ambiguity(&expr) {
+            let mut err = self.err_handler().struct_span_err(
+                span, &format!("ambigious use of `{}`", op_kind.to_string())
+            );
+
+            err.note(
+                "this will be a error until the `let_chains` feature is stabilized"
+            );
+            err.note(
+                "see rust-lang/rust#53668 for more information"
+            );
+
+            if let Ok(snippet) = self.session.source_map().span_to_snippet(span) {
+                err.span_suggestion(
+                    span, "consider adding parentheses", format!("({})", snippet),
+                );
+            }
+
+            err.emit();
+        }
+    }
+
+    /// With eRFC 2497 adding if-let chains, there is a requirement that the parsing of
+    /// `&&` and `||` in a if-let statement be unambigious. This function returns a span and
+    /// a `BinOpKind` (either `&&` or `||` depending on what was ambigious) if it is determined
+    /// that the current expression parsed is ambigious and will break in future.
+    fn while_if_let_expr_ambiguity(&self, expr: &P<Expr>) -> Option<(Span, BinOpKind)> {
+        debug!("while_if_let_expr_ambiguity: expr.node: {:?}", expr.node);
+        match &expr.node {
+            ExprKind::Binary(op, _, _) if op.node == BinOpKind::And || op.node == BinOpKind::Or => {
+                Some((expr.span, op.node))
+            },
+            ExprKind::Range(ref lhs, ref rhs, _) => {
+                let lhs_ambigious = lhs.as_ref()
+                    .and_then(|lhs| self.while_if_let_expr_ambiguity(lhs));
+                let rhs_ambigious = rhs.as_ref()
+                    .and_then(|rhs| self.while_if_let_expr_ambiguity(rhs));
+
+                lhs_ambigious.or(rhs_ambigious)
+            }
+            _ => None,
+        }
+    }
+
 }
 
 impl<'a> Visitor<'a> for AstValidator<'a> {
     fn visit_expr(&mut self, expr: &'a Expr) {
         match expr.node {
+            ExprKind::IfLet(_, ref expr, _, _) | ExprKind::WhileLet(_, ref expr, _, _) =>
+                self.while_if_let_ambiguity(&expr),
             ExprKind::InlineAsm(..) if !self.session.target.target.options.allow_asm => {
                 span_err!(self.session, expr.span, E0472, "asm! is unsupported on this target");
             }
diff --git a/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.rs b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.rs
new file mode 100644
index 00000000000..339d49104b0
--- /dev/null
+++ b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.rs
@@ -0,0 +1,49 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// edition:2015
+
+// Enabling `ireffutable_let_patterns` isn't necessary for what this tests, but it makes coming up
+// with examples easier.
+#![feature(irrefutable_let_patterns)]
+
+#[allow(irrefutable_let_patterns)]
+fn main() {
+    use std::ops::Range;
+
+    if let Range { start: _, end: _ } = true..true && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    if let Range { start: _, end: _ } = true..true || false { }
+    //~^ ERROR ambigious use of `||`
+
+    while let Range { start: _, end: _ } = true..true && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    while let Range { start: _, end: _ } = true..true || false { }
+    //~^ ERROR ambigious use of `||`
+
+    if let true = false && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    while let true = (1 == 2) && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    // The following cases are not an error as parenthesis are used to
+    // clarify intent:
+
+    if let Range { start: _, end: _ } = true..(true || false) { }
+
+    if let Range { start: _, end: _ } = true..(true && false) { }
+
+    while let Range { start: _, end: _ } = true..(true || false) { }
+
+    while let Range { start: _, end: _ } = true..(true && false) { }
+}
diff --git a/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.stderr b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.stderr
new file mode 100644
index 00000000000..8597294913f
--- /dev/null
+++ b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.stderr
@@ -0,0 +1,56 @@
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2015.rs:21:47
+   |
+LL |     if let Range { start: _, end: _ } = true..true && false { }
+   |                                               ^^^^^^^^^^^^^ help: consider adding parentheses: `(true && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `||`
+  --> $DIR/syntax-ambiguity-2015.rs:24:47
+   |
+LL |     if let Range { start: _, end: _ } = true..true || false { }
+   |                                               ^^^^^^^^^^^^^ help: consider adding parentheses: `(true || false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2015.rs:27:50
+   |
+LL |     while let Range { start: _, end: _ } = true..true && false { }
+   |                                                  ^^^^^^^^^^^^^ help: consider adding parentheses: `(true && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `||`
+  --> $DIR/syntax-ambiguity-2015.rs:30:50
+   |
+LL |     while let Range { start: _, end: _ } = true..true || false { }
+   |                                                  ^^^^^^^^^^^^^ help: consider adding parentheses: `(true || false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2015.rs:33:19
+   |
+LL |     if let true = false && false { }
+   |                   ^^^^^^^^^^^^^^ help: consider adding parentheses: `(false && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2015.rs:36:22
+   |
+LL |     while let true = (1 == 2) && false { }
+   |                      ^^^^^^^^^^^^^^^^^ help: consider adding parentheses: `((1 == 2) && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: aborting due to 6 previous errors
+
diff --git a/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.rs b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.rs
new file mode 100644
index 00000000000..baa90bcf8e9
--- /dev/null
+++ b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.rs
@@ -0,0 +1,49 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// edition:2018
+
+// Enabling `ireffutable_let_patterns` isn't necessary for what this tests, but it makes coming up
+// with examples easier.
+#![feature(irrefutable_let_patterns)]
+
+#[allow(irrefutable_let_patterns)]
+fn main() {
+    use std::ops::Range;
+
+    if let Range { start: _, end: _ } = true..true && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    if let Range { start: _, end: _ } = true..true || false { }
+    //~^ ERROR ambigious use of `||`
+
+    while let Range { start: _, end: _ } = true..true && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    while let Range { start: _, end: _ } = true..true || false { }
+    //~^ ERROR ambigious use of `||`
+
+    if let true = false && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    while let true = (1 == 2) && false { }
+    //~^ ERROR ambigious use of `&&`
+
+    // The following cases are not an error as parenthesis are used to
+    // clarify intent:
+
+    if let Range { start: _, end: _ } = true..(true || false) { }
+
+    if let Range { start: _, end: _ } = true..(true && false) { }
+
+    while let Range { start: _, end: _ } = true..(true || false) { }
+
+    while let Range { start: _, end: _ } = true..(true && false) { }
+}
diff --git a/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.stderr b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.stderr
new file mode 100644
index 00000000000..86ee04747b2
--- /dev/null
+++ b/src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.stderr
@@ -0,0 +1,56 @@
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2018.rs:21:47
+   |
+LL |     if let Range { start: _, end: _ } = true..true && false { }
+   |                                               ^^^^^^^^^^^^^ help: consider adding parentheses: `(true && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `||`
+  --> $DIR/syntax-ambiguity-2018.rs:24:47
+   |
+LL |     if let Range { start: _, end: _ } = true..true || false { }
+   |                                               ^^^^^^^^^^^^^ help: consider adding parentheses: `(true || false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2018.rs:27:50
+   |
+LL |     while let Range { start: _, end: _ } = true..true && false { }
+   |                                                  ^^^^^^^^^^^^^ help: consider adding parentheses: `(true && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `||`
+  --> $DIR/syntax-ambiguity-2018.rs:30:50
+   |
+LL |     while let Range { start: _, end: _ } = true..true || false { }
+   |                                                  ^^^^^^^^^^^^^ help: consider adding parentheses: `(true || false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2018.rs:33:19
+   |
+LL |     if let true = false && false { }
+   |                   ^^^^^^^^^^^^^^ help: consider adding parentheses: `(false && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: ambigious use of `&&`
+  --> $DIR/syntax-ambiguity-2018.rs:36:22
+   |
+LL |     while let true = (1 == 2) && false { }
+   |                      ^^^^^^^^^^^^^^^^^ help: consider adding parentheses: `((1 == 2) && false)`
+   |
+   = note: this will be a error until the `let_chains` feature is stabilized
+   = note: see rust-lang/rust#53668 for more information
+
+error: aborting due to 6 previous errors
+