Fix serialization bug in edition field of TomlProject.

src/cargo/util/toml/mod.rs

@@ -568,8 +568,15 @@ impl<'de> de::Deserialize<'de> for VecStringOrBool {
     }
 }
 
+/// Represents the `package`/`project` sections of a `Cargo.toml`.
+///
+/// Note that the order of the fields matters, since this is the order they
+/// are serialized to a TOML file.  For example, you cannot have values after
+/// the field `metadata`, since it is a table and values cannot appear after
+/// tables.
 #[derive(Deserialize, Serialize, Clone, Debug)]
 pub struct TomlProject {
+    edition: Option<String>,
     name: String,
     version: semver::Version,
     authors: Option<Vec<String>>,
@@ -604,7 +611,6 @@ pub struct TomlProject {
     license_file: Option<String>,
     repository: Option<String>,
     metadata: Option<toml::Value>,
-    edition: Option<String>,
 }
 
 #[derive(Debug, Deserialize, Serialize)]

tests/testsuite/package.rs

@@ -967,6 +967,32 @@ fn test_edition() {
     );
 }
 
+#[test]
+fn edition_with_metadata() {
+    if !is_nightly() { // --edition is nightly-only
+        return;
+    }
+
+    let p = project()
+        .file("Cargo.toml", r#"
+            cargo-features = ["edition"]
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+            edition = "2018"
+            [package.metadata.docs.rs]
+            features = ["foobar"]
+        "#)
+        .file("src/lib.rs", "")
+        .build();
+
+    assert_that(
+        p.cargo("package").masquerade_as_nightly_cargo(),
+        execs(),
+    );
+}
+
 #[test]
 fn test_edition_missing() {
     // no edition = 2015