Auto merge of #52355 - pietroalbini:zfeature, r=eddyb

Add the -Zcrate-attr=foo unstable rustc option

This PR adds a new unstable option to `rustc`: `-Zcrate-attr=foo`. The option can be used to inject crate-level attributes from the CLI, and it's meant to be used by tools like Crater that needs to add their own attributes to a crate without changing the source code.

The exact reason I need this is to implement "edition runs" in Crater: we need to add the preview feature flag to every crate, and editing the crates' source code on the fly might produce unexpected results, while a compiler flag is more reliable.

cc rust-lang/crater#282 @Mark-Simulacrum

src/librustc/ich/impls_syntax.rs

@@ -423,6 +423,7 @@ impl_stable_hash_for!(enum ::syntax_pos::FileName {
     Anon,
     MacroExpansion,
     ProcMacroSourceCode,
+    CliCrateAttr,
     CfgSpec,
     Custom(s)
 });

src/librustc/session/config.rs

@@ -1367,6 +1367,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "don't run LLVM in parallel (while keeping codegen-units and ThinLTO)"),
     no_leak_check: bool = (false, parse_bool, [UNTRACKED],
         "disables the 'leak check' for subtyping; unsound, but useful for tests"),
+    crate_attr: Vec<String> = (Vec::new(), parse_string_push, [TRACKED],
+        "inject the given attribute in the crate"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_driver/driver.rs

@@ -798,7 +798,7 @@ where
 pub fn phase_2_configure_and_expand_inner<'a, F>(
     sess: &'a Session,
     cstore: &'a CStore,
-    krate: ast::Crate,
+    mut krate: ast::Crate,
     registry: Option<Registry>,
     crate_name: &str,
     addl_plugins: Option<Vec<String>>,
@@ -810,6 +810,10 @@ pub fn phase_2_configure_and_expand_inner<'a, F>(
 where
     F: FnOnce(&ast::Crate) -> CompileResult,
 {
+    krate = time(sess, "attributes injection", || {
+        syntax::attr::inject(krate, &sess.parse_sess, &sess.opts.debugging_opts.crate_attr)
+    });
+
     let (mut krate, features) = syntax::config::features(
         krate,
         &sess.parse_sess,

src/libsyntax/attr/mod.rs

@@ -22,11 +22,11 @@ pub use self::ReprAttr::*;
 pub use self::StabilityLevel::*;
 
 use ast;
-use ast::{AttrId, Attribute, Name, Ident, Path, PathSegment};
+use ast::{AttrId, Attribute, AttrStyle, Name, Ident, Path, PathSegment};
 use ast::{MetaItem, MetaItemKind, NestedMetaItem, NestedMetaItemKind};
 use ast::{Lit, LitKind, Expr, ExprKind, Item, Local, Stmt, StmtKind, GenericParam};
 use codemap::{BytePos, Spanned, respan, dummy_spanned};
-use syntax_pos::Span;
+use syntax_pos::{FileName, Span};
 use parse::lexer::comments::{doc_comment_style, strip_doc_comment_decoration};
 use parse::parser::Parser;
 use parse::{self, ParseSess, PResult};
@@ -821,3 +821,33 @@ derive_has_attrs! {
     Item, Expr, Local, ast::ForeignItem, ast::StructField, ast::ImplItem, ast::TraitItem, ast::Arm,
     ast::Field, ast::FieldPat, ast::Variant_
 }
+
+pub fn inject(mut krate: ast::Crate, parse_sess: &ParseSess, attrs: &[String]) -> ast::Crate {
+    for raw_attr in attrs {
+        let mut parser = parse::new_parser_from_source_str(
+            parse_sess,
+            FileName::CliCrateAttr,
+            raw_attr.clone(),
+        );
+
+        let start_span = parser.span;
+        let (path, tokens) = panictry!(parser.parse_path_and_tokens());
+        let end_span = parser.span;
+        if parser.token != token::Eof {
+            parse_sess.span_diagnostic
+                .span_err(start_span.to(end_span), "invalid crate attribute");
+            continue;
+        }
+
+        krate.attrs.push(Attribute {
+            id: mk_attr_id(),
+            style: AttrStyle::Inner,
+            path,
+            tokens,
+            is_sugared_doc: false,
+            span: start_span.to(end_span),
+        });
+    }
+
+    krate
+}

src/libsyntax_pos/lib.rs

@@ -98,6 +98,8 @@ pub enum FileName {
     ProcMacroSourceCode,
     /// Strings provided as --cfg [cfgspec] stored in a crate_cfg
     CfgSpec,
+    /// Strings provided as crate attributes in the CLI
+    CliCrateAttr,
     /// Custom sources for explicit parser calls from plugins and drivers
     Custom(String),
 }
@@ -113,6 +115,7 @@ impl std::fmt::Display for FileName {
             Anon => write!(fmt, "<anon>"),
             ProcMacroSourceCode => write!(fmt, "<proc-macro source code>"),
             CfgSpec => write!(fmt, "cfgspec"),
+            CliCrateAttr => write!(fmt, "<crate attribute>"),
             Custom(ref s) => write!(fmt, "<{}>", s),
         }
     }
@@ -135,6 +138,7 @@ impl FileName {
             MacroExpansion |
             ProcMacroSourceCode |
             CfgSpec |
+            CliCrateAttr |
             Custom(_) |
             QuoteExpansion => false,
         }
@@ -148,6 +152,7 @@ impl FileName {
             MacroExpansion |
             ProcMacroSourceCode |
             CfgSpec |
+            CliCrateAttr |
             Custom(_) |
             QuoteExpansion => false,
             Macros(_) => true,

src/test/run-pass/z-crate-attr.rs

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// This test checks if an unstable feature is enabled with the -Zcrate-attr=feature(foo) flag. If
+// the exact feature used here is causing problems feel free to replace it with another
+// perma-unstable feature.
+
+// compile-flags: -Zcrate-attr=feature(abi_unadjusted)
+
+#![allow(dead_code)]
+
+extern "unadjusted" fn foo() {}
+
+fn main() {}