Add metadata suffix, close rust-lang/cargo#4028

Author: ishitatsuyuki

src/bootstrap/bin/rustc.rs

@@ -38,7 +38,24 @@ use std::path::PathBuf;
 use std::process::{Command, ExitStatus};
 
 fn main() {
-    let args = env::args_os().skip(1).collect::<Vec<_>>();
+    let mut args = env::args_os().skip(1).collect::<Vec<_>>();
+
+    // Append metadata suffix for internal crates. See the corresponding entry
+    // in bootstrap/lib.rs for details.
+    if let Ok(s) = env::var("RUSTC_METADATA_SUFFIX") {
+        for i in 1..args.len() {
+            // Dirty code for borrowing issues
+            let mut new = None;
+            if let Some(current_as_str) = args[i].to_str() {
+                if (&*args[i - 1] == "-C" && current_as_str.starts_with("metadata")) ||
+                   current_as_str.starts_with("-Cmetadata") {
+                    new = Some(format!("{}-{}", current_as_str, s));
+                }
+            }
+            if let Some(new) = new { args[i] = new.into(); }
+        }
+    }
+
     // Detect whether or not we're a build script depending on whether --target
     // is passed (a bit janky...)
     let target = args.windows(2)

src/bootstrap/lib.rs

@@ -475,12 +475,30 @@ impl Build {
              .env("RUSTDOC_REAL", self.rustdoc(compiler))
              .env("RUSTC_FLAGS", self.rustc_flags(target).join(" "));
 
-        // Tools don't get debuginfo right now, e.g. cargo and rls don't get
-        // compiled with debuginfo.
         if mode != Mode::Tool {
-             cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
-                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string())
-                  .env("RUSTC_FORCE_UNSTABLE", "1");
+            // Tools don't get debuginfo right now, e.g. cargo and rls don't
+            // get compiled with debuginfo.
+            cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
+                 .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string())
+                 .env("RUSTC_FORCE_UNSTABLE", "1");
+
+            // Currently the compiler depends on crates from crates.io, and
+            // then other crates can depend on the compiler (e.g. proc-macro
+            // crates). Let's say, for example that rustc itself depends on the
+            // bitflags crate. If an external crate then depends on the
+            // bitflags crate as well, we need to make sure they don't
+            // conflict, even if they pick the same verison of bitflags. We'll
+            // want to make sure that e.g. a plugin and rustc each get their
+            // own copy of bitflags.
+
+            // Cargo ensures that this works in general through the -C metadata
+            // flag. This flag will frob the symbols in the binary to make sure
+            // they're different, even though the source code is the exact
+            // same. To solve this problem for the compiler we extend Cargo's
+            // already-passed -C metadata flag with our own. Our rustc.rs
+            // wrapper around the actual rustc will detect -C metadata being
+            // passed and frob it with this extra string we're passing in.
+            cargo.env("RUSTC_METADATA_SUFFIX", "rustc");
         }
 
         // Enable usage of unstable features