Switch to using --edition

Fixes #5406

Author: dwijnand

src/cargo/core/compiler/mod.rs

@@ -911,7 +911,7 @@ fn build_base_args<'a, 'cfg>(
     let manifest = unit.pkg.manifest();
 
     if manifest.features().is_enabled(Feature::edition()) {
-        cmd.arg(format!("-Zedition={}", manifest.edition()));
+        cmd.arg(format!("--edition={}", manifest.edition()));
     }
 
     // Disable LTO for host builds as prefer_dynamic and it are mutually

tests/testsuite/package.rs

@@ -1125,7 +1125,7 @@ fn test_edition() {
                 .with_stderr_contains(format!("\
 [COMPILING] foo v0.0.1 ({url})
 [RUNNING] `rustc --crate-name foo src[/]lib.rs --crate-type lib \
-        --emit=dep-info,link -Zedition=2018 -C debuginfo=2 \
+        --emit=dep-info,link --edition=2018 -C debuginfo=2 \
         -C metadata=[..] \
         --out-dir [..] \
         -L dependency={dir}[/]target[/]debug[/]deps`
@@ -1159,7 +1159,7 @@ fn test_edition_missing() {
                 .with_stderr_contains(format!("\
 [COMPILING] foo v0.0.1 ({url})
 [RUNNING] `rustc --crate-name foo src[/]lib.rs --crate-type lib \
-        --emit=dep-info,link -Zedition=2015 -C debuginfo=2 \
+        --emit=dep-info,link --edition=2015 -C debuginfo=2 \
         -C metadata=[..] \
         --out-dir [..] \
         -L dependency={dir}[/]target[/]debug[/]deps`