Pass --edition after --crate-name

This PR swaps the order of the --edition and --crate-name args in the
rustc invocation.

    Before: rustc --edition=2018 --crate-name cargo ...
    After: rustc --crate-name cargo --edition=2018 ...

The crate name is a lot more relevant when looking at processes in top
for example, and should appear first.

Author: dtolnay

src/cargo/core/compiler/compilation.rs

@@ -119,12 +119,7 @@ impl<'cfg> Compilation<'cfg> {
     }
 
     /// See `process`.
-    pub fn rustc_process(
-        &self,
-        pkg: &Package,
-        target: &Target,
-        is_primary: bool,
-    ) -> CargoResult<ProcessBuilder> {
+    pub fn rustc_process(&self, pkg: &Package, is_primary: bool) -> CargoResult<ProcessBuilder> {
         let rustc = if is_primary {
             self.primary_unit_rustc_process
                 .clone()
@@ -133,11 +128,7 @@ impl<'cfg> Compilation<'cfg> {
             self.rustc_process.clone()
         };
 
-        let mut p = self.fill_env(rustc, pkg, true)?;
-        if target.edition() != Edition::Edition2015 {
-            p.arg(format!("--edition={}", target.edition()));
-        }
-        Ok(p)
+        self.fill_env(rustc, pkg, true)
     }
 
     /// See `process`.

src/cargo/core/compiler/mod.rs

@@ -43,7 +43,7 @@ use self::unit_dependencies::UnitDep;
 pub use crate::core::compiler::unit::{Unit, UnitInterner};
 use crate::core::manifest::TargetSourcePath;
 use crate::core::profiles::{Lto, PanicStrategy, Profile};
-use crate::core::{Feature, InternedString, PackageId, Target};
+use crate::core::{Edition, Feature, InternedString, PackageId, Target};
 use crate::util::errors::{self, CargoResult, CargoResultExt, Internal, ProcessError};
 use crate::util::machine_message::Message;
 use crate::util::paths;
@@ -538,9 +538,7 @@ fn prepare_rustc<'a, 'cfg>(
 ) -> CargoResult<ProcessBuilder> {
     let is_primary = cx.is_primary_package(unit);
 
-    let mut base = cx
-        .compilation
-        .rustc_process(unit.pkg, unit.target, is_primary)?;
+    let mut base = cx.compilation.rustc_process(unit.pkg, is_primary)?;
     base.inherit_jobserver(&cx.jobserver);
     build_base_args(cx, &mut base, unit, crate_types)?;
     build_deps_args(&mut base, cx, unit)?;
@@ -714,6 +712,11 @@ fn build_base_args<'a, 'cfg>(
 
     cmd.arg("--crate-name").arg(&unit.target.crate_name());
 
+    let edition = unit.target.edition();
+    if edition != Edition::Edition2015 {
+        cmd.arg(format!("--edition={}", edition));
+    }
+
     add_path_args(bcx, unit, cmd);
     add_error_format_and_color(cx, cmd, cx.rmeta_required(unit))?;