fix: non-mergeable list from config cli merge the same way

Before we iterated key values directly for config cli values,
so top level table name of config key is never tracked.
And that resulted in
`registries.example.credential-provider` becoming
`example.credential-provider`,
making `is_nonmergable_list` return false.

This fix replaces the manual traversal
with a direct `ConfigValue::merge` call.

Now we unify how config values merge, regardless theird sources.

Author: weihanglo

src/cargo/util/context/mod.rs

@@ -1546,24 +1546,18 @@ impl GlobalContext {
 
     /// Add config arguments passed on the command line.
     fn merge_cli_args(&mut self) -> CargoResult<()> {
-        let CV::Table(loaded_map, _def) = self.cli_args_as_table()? else {
-            unreachable!()
-        };
-        let values = self.values_mut()?;
-        for (key, value) in loaded_map.into_iter() {
-            match values.entry(key) {
-                Vacant(entry) => {
-                    entry.insert(value);
-                }
-                Occupied(mut entry) => entry.get_mut().merge(value, true).with_context(|| {
-                    format!(
-                        "failed to merge --config key `{}` into `{}`",
-                        entry.key(),
-                        entry.get().definition(),
-                    )
-                })?,
-            };
-        }
+        let cv_from_cli = self.cli_args_as_table()?;
+        assert!(cv_from_cli.is_table(), "cv from CLI must be a table");
+
+        let root_cv = mem::take(self.values_mut()?);
+        // This definition path is ignored, this is just a temporary container
+        // representing the entire file.
+        let mut root_cv = CV::Table(root_cv, Definition::Path(PathBuf::from(".")));
+        root_cv.merge(cv_from_cli, true)?;
+
+        // Put it back to gctx
+        mem::swap(self.values_mut()?, root_cv.table_mut("<root>")?.0);
+
         Ok(())
     }
 
@@ -2299,6 +2293,20 @@ impl ConfigValue {
         }
     }
 
+    pub fn table_mut(
+        &mut self,
+        key: &str,
+    ) -> CargoResult<(&mut HashMap<String, ConfigValue>, &mut Definition)> {
+        match self {
+            CV::Table(table, def) => Ok((table, def)),
+            _ => self.expected("table", key),
+        }
+    }
+
+    pub fn is_table(&self) -> bool {
+        matches!(self, CV::Table(_table, _def))
+    }
+
     pub fn string_list(&self, key: &str) -> CargoResult<Vec<(String, Definition)>> {
         match self {
             CV::List(list, _) => list

tests/testsuite/config.rs

@@ -652,7 +652,7 @@ Caused by:
     assert_error(
         gctx.unwrap_err(),
         str![[r#"
-failed to merge --config key `a` into `[ROOT]/.cargo/config.toml`
+failed to merge key `a` between [ROOT]/.cargo/config.toml and --config cli option
 
 Caused by:
   failed to merge config value from `--config cli option` into `[ROOT]/.cargo/config.toml`: expected boolean, but found array
@@ -2222,8 +2222,8 @@ credential-provider = ['c', 'd']
         .credential_provider
         .unwrap();
     // expect: no merge happens; config CLI takes precedence
-    assert_eq!(provider.path.raw_value(), "c");
-    assert_eq!(provider.args, ["d", "cli", "cli-arg"]);
+    assert_eq!(provider.path.raw_value(), "cli");
+    assert_eq!(provider.args, ["cli-arg"]);
 }
 
 #[cargo_test]

tests/testsuite/config_include.rs

@@ -459,7 +459,7 @@ fn cli_merge_failed() {
     assert_error(
         gctx.unwrap_err(),
         str![[r#"
-failed to merge --config key `foo` into `[ROOT]/.cargo/config.toml`
+failed to merge key `foo` between [ROOT]/.cargo/config.toml and [ROOT]/.cargo/other.toml
 
 Caused by:
   failed to merge config value from `[ROOT]/.cargo/other.toml` into `[ROOT]/.cargo/config.toml`: expected array, but found string