WIP: fix(config): Improve the error for partial-struct

src/cargo/util/context/mod.rs

@@ -1939,7 +1939,7 @@ impl GlobalContext {
             key: ConfigKey::from_str(key),
             env_prefix_ok: true,
         };
-        T::deserialize(d).map_err(|e| e.into())
+        T::deserialize(d).with_context(|| format!("failed to read `{key}` config field"))
     }
 
     /// Obtain a [`Path`] from a [`Filesystem`], verifying that the

tests/testsuite/config.rs

@@ -1801,3 +1801,71 @@ fn trim_paths_parsing() {
     let trim_paths: TomlTrimPaths = gctx.get("profile.dev.trim-paths").unwrap();
     assert_eq!(trim_paths, expected, "failed to parse {val}");
 }
+
+#[cargo_test]
+fn incomplete_cli() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            edition = "2015"
+            authors = []
+            rust-version = "1.1.1"
+            [[bin]]
+            name = "foo"
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("check")
+        .arg("--config=term.progress.width=2")
+        .with_status(101)
+        .with_stdout("")
+        .with_stderr(
+            "\
+error: failed to read `term` config field
+
+Caused by:
+  missing field `when`
+",
+        )
+        .run();
+}
+
+#[cargo_test]
+fn incomplete_env() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            edition = "2015"
+            authors = []
+            rust-version = "1.1.1"
+            [[bin]]
+            name = "foo"
+        "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("check")
+        .env("CARGO_TERM_PROGRESS_WIDTH", "2")
+        .with_status(101)
+        .with_stdout("")
+        .with_stderr(
+            "\
+error: failed to read `term` config field
+
+Caused by:
+  missing field `when`
+",
+        )
+        .run();
+}