cfg_attr_multi: Basic implementation

Does not implement the warning or a feature flag.

Author: Havvy

src/libsyntax/config.rs

@@ -73,49 +73,76 @@ impl<'a> StripUnconfigured<'a> {
         if self.in_cfg(node.attrs()) { Some(node) } else { None }
     }
 
+    /// Parse and expand all `cfg_attr` attributes into a list of attributes
+    /// that are within each `cfg_attr` that has a true configuration predicate.
+    ///
+    /// Gives compiler warnigns if any `cfg_attr` does not contain any
+    /// attributes and is in the original source code. Gives compiler errors if
+    /// the syntax of any `cfg_attr` is incorrect.
     pub fn process_cfg_attrs<T: HasAttrs>(&mut self, node: T) -> T {
         node.map_attrs(|attrs| {
-            attrs.into_iter().filter_map(|attr| self.process_cfg_attr(attr)).collect()
+            attrs.into_iter().flat_map(|attr| self.process_cfg_attr(attr)).collect()
         })
     }
 
-    fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Option<ast::Attribute> {
+    /// Parse and expand a single `cfg_attr` attribute into a list of attributes
+    /// when the configuration predicate is true, or otherwise expand into an
+    /// empty list of attributes.
+    ///
+    /// Gives a compiler warning when the `cfg_attr` contains no attribtes and
+    /// is in the original source file. Gives a compiler error if the syntax of
+    /// the attribute is incorrect
+    fn process_cfg_attr(&mut self, attr: ast::Attribute) -> Vec<ast::Attribute> {
         if !attr.check_name("cfg_attr") {
-            return Some(attr);
+            return vec![attr];
         }
 
-        let (cfg, path, tokens, span) = match attr.parse(self.sess, |parser| {
+        let (cfg_predicate, expanded_attrs) = match attr.parse(self.sess, |parser| {
             parser.expect(&token::OpenDelim(token::Paren))?;
-            let cfg = parser.parse_meta_item()?;
+
+            let cfg_predicate = parser.parse_meta_item()?;
             parser.expect(&token::Comma)?;
-            let lo = parser.span.lo();
-            let (path, tokens) = parser.parse_meta_item_unrestricted()?;
-            parser.eat(&token::Comma); // Optional trailing comma
+
+            // Presumably, the majority of the time there will only be one attr.
+            let mut expanded_attrs = Vec::with_capacity(1);
+
+            while !parser.check(&token::CloseDelim(token::Paren)) {
+                let lo = parser.span.lo();
+                let (path, tokens) = parser.parse_meta_item_unrestricted()?;
+                expanded_attrs.push((path, tokens, parser.prev_span.with_lo(lo)));
+                parser.expect_one_of(&[token::Comma], &[token::CloseDelim(token::Paren)])?;
+            }
+
             parser.expect(&token::CloseDelim(token::Paren))?;
-            Ok((cfg, path, tokens, parser.prev_span.with_lo(lo)))
+            Ok((cfg_predicate, expanded_attrs))
         }) {
             Ok(result) => result,
             Err(mut e) => {
                 e.emit();
-                return None;
+                return Vec::new();
             }
         };
 
-        if attr::cfg_matches(&cfg, self.sess, self.features) {
-            self.process_cfg_attr(ast::Attribute {
+        if attr::cfg_matches(&cfg_predicate, self.sess, self.features) {
+            // We call `process_cfg_attr` recursively in case there's a
+            // `cfg_attr` inside of another `cfg_attr`. E.g.
+            //  `#[cfg_attr(false, cfg_attr(true, some_attr))]`.
+            expanded_attrs.into_iter()
+            .flat_map(|(path, tokens, span)| self.process_cfg_attr(ast::Attribute {
                 id: attr::mk_attr_id(),
                 style: attr.style,
                 path,
                 tokens,
                 is_sugared_doc: false,
                 span,
-            })
+            }))
+            .collect()
         } else {
-            None
+            Vec::new()
         }
     }
 
-    // Determine if a node with the given attributes should be included in this configuration.
+    /// Determine if a node with the given attributes should be included in this configuration.
     pub fn in_cfg(&mut self, attrs: &[ast::Attribute]) -> bool {
         attrs.iter().all(|attr| {
             if !is_cfg(attr) {
@@ -165,7 +192,7 @@ impl<'a> StripUnconfigured<'a> {
         })
     }
 
-    // Visit attributes on expression and statements (but not attributes on items in blocks).
+    /// Visit attributes on expression and statements (but not attributes on items in blocks).
     fn visit_expr_attrs(&mut self, attrs: &[ast::Attribute]) {
         // flag the offending attributes
         for attr in attrs.iter() {

src/libsyntax/parse/parser.rs

@@ -678,7 +678,7 @@ impl<'a> Parser<'a> {
     /// Expect next token to be edible or inedible token.  If edible,
     /// then consume it; if inedible, then return without consuming
     /// anything.  Signal a fatal error if next token is unexpected.
-    fn expect_one_of(&mut self,
+    pub fn expect_one_of(&mut self,
                          edible: &[token::Token],
                          inedible: &[token::Token]) -> PResult<'a,  ()>{
         fn tokens_to_string(tokens: &[TokenType]) -> String {

src/test/ui/cfg-attr-trailing-comma.rs

@@ -2,7 +2,7 @@ error[E0658]: no_core is experimental (see issue #29639)
   --> $DIR/cfg-attr-crate-2.rs:15:21
    |
 LL | #![cfg_attr(broken, no_core)] //~ ERROR no_core is experimental
-   |                     ^^^^^^^^
+   |                     ^^^^^^^
    |
    = help: add #![feature(no_core)] to the crate attributes to enable
 

src/test/ui/cfg-attr-trailing-comma.stderr

@@ -0,0 +1,19 @@
+// Test that cfg_attr doesn't emit any attributes when the
+// configuation variable is false. This mirrors `cfg-attr-multi-true.rs`
+
+// compile-pass
+
+#![warn(unused_must_use)]
+
+#[cfg_attr(any(), deprecated, must_use)]
+struct Struct {}
+
+impl Struct {
+    fn new() -> Struct {
+        Struct {}
+    }
+}
+
+fn main() {
+    Struct::new();
+}

src/test/ui/conditional-compilation/cfg-attr-crate-2.stderr

@@ -0,0 +1,15 @@
+// Copyright 2015 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.
+//
+// compile-flags: --cfg broken
+
+#![cfg_attr(broken, no_core, no_std)] //~ ERROR no_core is experimental
+
+fn main() { }

src/test/ui/conditional-compilation/cfg-attr-multi-false.rs

@@ -0,0 +1,11 @@
+error[E0658]: no_core is experimental (see issue #29639)
+  --> $DIR/cfg-attr-multi-invalid-1.rs:13:21
+   |
+LL | #![cfg_attr(broken, no_core, no_std)] //~ ERROR no_core is experimental
+   |                     ^^^^^^^
+   |
+   = help: add #![feature(no_core)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/conditional-compilation/cfg-attr-multi-invalid-1.rs

@@ -0,0 +1,15 @@
+// Copyright 2015 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.
+//
+// compile-flags: --cfg broken
+
+#![cfg_attr(broken, no_std, no_core)] //~ ERROR no_core is experimental
+
+fn main() { }

src/test/ui/conditional-compilation/cfg-attr-multi-invalid-1.stderr

@@ -0,0 +1,11 @@
+error[E0658]: no_core is experimental (see issue #29639)
+  --> $DIR/cfg-attr-multi-invalid-2.rs:13:29
+   |
+LL | #![cfg_attr(broken, no_std, no_core)] //~ ERROR no_core is experimental
+   |                             ^^^^^^^
+   |
+   = help: add #![feature(no_core)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/conditional-compilation/cfg-attr-multi-invalid-2.rs

@@ -0,0 +1,21 @@
+// Test that cfg_attr with multiple attributes actually emits both attributes.
+// This is done by emitting two attributes that cause new warnings, and then
+// triggering those warnings.
+
+// compile-pass
+
+#![warn(unused_must_use)]
+
+#[cfg_attr(all(), deprecated, must_use)]
+struct MustUseDeprecated {}
+
+impl MustUseDeprecated { //~ warning: use of deprecated item
+    fn new() -> MustUseDeprecated { //~ warning: use of deprecated item
+        MustUseDeprecated {} //~ warning: use of deprecated item
+    }
+}
+
+fn main() {
+    MustUseDeprecated::new(); //~ warning: use of deprecated item
+    //| warning: unused `MustUseDeprecated` which must be used
+}

src/test/ui/conditional-compilation/cfg-attr-multi-invalid-2.stderr

@@ -0,0 +1,38 @@
+warning: use of deprecated item 'MustUseDeprecated'
+  --> $DIR/cfg-attr-multi-true.rs:12:6
+   |
+LL | impl MustUseDeprecated { //~ warning: use of deprecated item
+   |      ^^^^^^^^^^^^^^^^^
+   |
+   = note: #[warn(deprecated)] on by default
+
+warning: use of deprecated item 'MustUseDeprecated'
+  --> $DIR/cfg-attr-multi-true.rs:19:5
+   |
+LL |     MustUseDeprecated::new(); //~ warning: use of deprecated item
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+warning: use of deprecated item 'MustUseDeprecated'
+  --> $DIR/cfg-attr-multi-true.rs:13:17
+   |
+LL |     fn new() -> MustUseDeprecated { //~ warning: use of deprecated item
+   |                 ^^^^^^^^^^^^^^^^^
+
+warning: use of deprecated item 'MustUseDeprecated'
+  --> $DIR/cfg-attr-multi-true.rs:14:9
+   |
+LL |         MustUseDeprecated {} //~ warning: use of deprecated item
+   |         ^^^^^^^^^^^^^^^^^
+
+warning: unused `MustUseDeprecated` which must be used
+  --> $DIR/cfg-attr-multi-true.rs:19:5
+   |
+LL |     MustUseDeprecated::new(); //~ warning: use of deprecated item
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/cfg-attr-multi-true.rs:7:9
+   |
+LL | #![warn(unused_must_use)]
+   |         ^^^^^^^^^^^^^^^
+

src/test/ui/conditional-compilation/cfg-attr-multi-true.rs

@@ -0,0 +1,45 @@
+// Parse `cfg_attr` with varying numbers of attributes and trailing commas
+
+#![feature(cfg_attr_multi)]
+
+// Completely empty `cfg_attr` input
+#[cfg_attr()] //~ error: expected identifier, found `)`
+struct NoConfigurationPredicate;
+
+// Zero attributes, zero trailing comma (comma manatory here)
+#[cfg_attr(all())] //~ error: expected `,`, found `)`
+struct A0C0;
+
+// Zero attributes, one trailing comma
+#[cfg_attr(all(),)] // Ok
+struct A0C1;
+
+// Zero attributes, two trailing commas
+#[cfg_attr(all(),,)] //~ ERROR expected identifier
+struct A0C2;
+
+// One attribute, no trailing comma
+#[cfg_attr(all(), must_use)] // Ok
+struct A1C0;
+
+// One attribute, one trailing comma
+#[cfg_attr(all(), must_use,)] // Ok
+struct A1C1;
+
+// One attribute, two trailing commas
+#[cfg_attr(all(), must_use,,)] //~ ERROR expected identifier
+struct A1C2;
+
+// Two attributes, no trailing comma
+#[cfg_attr(all(), must_use, deprecated)] // Ok
+struct A2C0;
+
+// Two attributes, one trailing comma
+#[cfg_attr(all(), must_use, deprecated,)] // Ok
+struct A2C1;
+
+// Two attributes, two trailing commas
+#[cfg_attr(all(), must_use, deprecated,,)] //~ ERROR expected identifier
+struct A2C2;
+
+fn main() {}

src/test/ui/conditional-compilation/cfg-attr-multi-true.stderr

@@ -0,0 +1,32 @@
+error: expected identifier, found `)`
+  --> $DIR/cfg-attr-parse.rs:6:12
+   |
+LL | #[cfg_attr()] //~ error: expected identifier, found `)`
+   |            ^ expected identifier
+
+error: expected `,`, found `)`
+  --> $DIR/cfg-attr-parse.rs:10:17
+   |
+LL | #[cfg_attr(all())] //~ error: expected `,`, found `)`
+   |                 ^ expected `,`
+
+error: expected identifier, found `,`
+  --> $DIR/cfg-attr-parse.rs:18:18
+   |
+LL | #[cfg_attr(all(),,)] //~ ERROR expected identifier
+   |                  ^ expected identifier
+
+error: expected identifier, found `,`
+  --> $DIR/cfg-attr-parse.rs:30:28
+   |
+LL | #[cfg_attr(all(), must_use,,)] //~ ERROR expected identifier
+   |                            ^ expected identifier
+
+error: expected identifier, found `,`
+  --> $DIR/cfg-attr-parse.rs:42:40
+   |
+LL | #[cfg_attr(all(), must_use, deprecated,,)] //~ ERROR expected identifier
+   |                                        ^ expected identifier
+
+error: aborting due to 5 previous errors
+