feat(config-include): support inline and array of tables

Both are now supported

```
include = ['simple.toml', { path = 'other.toml' }]
```

```
[[include]]
path = 'first.toml'

[[include]]
path = 'second.toml'
```

So in the future we can extend field like `optional` or `if`
in the include table

On the implementation side,
`ConfigInclude` intentionally doesn't derive serde deserialization
to avoid any misuse of `GlobalContext::get::<ConfigInclude>()`,
which might lead to wrong config loading order.

Author: weihanglo

src/cargo/util/context/mod.rs

@@ -1400,8 +1400,20 @@ impl GlobalContext {
                 .enumerate()
                 .map(|(idx, cv)| match cv {
                     CV::String(s, def) => Ok(ConfigInclude::new(s, def)),
+                    CV::Table(mut table, def) => {
+                        // Extract `include.path`
+                        let s = match table.remove("path") {
+                            Some(CV::String(s, _)) => s,
+                            Some(other) => bail!(
+                                "expected a string, but found {} at `include[{idx}].path` in `{def}`",
+                                other.desc()
+                            ),
+                            None => bail!("missing field `path` at `include[{idx}]` in `{def}`"),
+                        };
+                        Ok(ConfigInclude::new(s, def))
+                    }
                     other => bail!(
-                        "expected a string, but found {} at `include[{idx}]` in `{}",
+                        "expected a string or table, but found {} at `include[{idx}]` in {}",
                         other.desc(),
                         other.definition(),
                     ),
@@ -2473,6 +2485,11 @@ pub fn save_credentials(
     }
 }
 
+/// Represents a config-include value in the configuration.
+///
+/// This intentionally doesn't derive serde deserialization
+/// to avoid any misuse of `GlobalContext::get::<ConfigInclude>()`,
+/// which might lead to wrong config loading order.
 struct ConfigInclude {
     /// Path to a config-include configuration file.
     /// Could be either relative or absolute.

tests/testsuite/config_include.rs

@@ -520,19 +520,13 @@ fn inline_table_style() {
         ",
     );
 
-    // Currently this fails with an error
     let gctx = GlobalContextBuilder::new()
         .unstable_flag("config-include")
-        .build_err();
-    assert_error(
-        gctx.unwrap_err(),
-        str![[r#"
-could not load Cargo configuration
-
-Caused by:
-  expected a string, but found table at `include[1]` in `[ROOT]/.cargo/config.toml
-"#]],
-    );
+        .build();
+    assert_eq!(gctx.get::<i32>("key1").unwrap(), 1);
+    assert_eq!(gctx.get::<i32>("key2").unwrap(), 2);
+    assert_eq!(gctx.get::<i32>("key3").unwrap(), 5);
+    assert_eq!(gctx.get::<i32>("key4").unwrap(), 6);
 }
 
 #[cargo_test]
@@ -565,19 +559,13 @@ fn array_of_tables_style() {
         ",
     );
 
-    // Currently this also fails with an error
     let gctx = GlobalContextBuilder::new()
         .unstable_flag("config-include")
-        .build_err();
-    assert_error(
-        gctx.unwrap_err(),
-        str![[r#"
-could not load Cargo configuration
-
-Caused by:
-  expected a string, but found table at `include[0]` in `[ROOT]/.cargo/config.toml
-"#]],
-    );
+        .build();
+    assert_eq!(gctx.get::<i32>("key1").unwrap(), 1);
+    assert_eq!(gctx.get::<i32>("key2").unwrap(), 2);
+    assert_eq!(gctx.get::<i32>("key3").unwrap(), 5);
+    assert_eq!(gctx.get::<i32>("key4").unwrap(), 6);
 }
 
 #[cargo_test]
@@ -603,16 +591,9 @@ fn table_with_unknown_fields() {
 
     let gctx = GlobalContextBuilder::new()
         .unstable_flag("config-include")
-        .build_err();
-    assert_error(
-        gctx.unwrap_err(),
-        str![[r#"
-could not load Cargo configuration
-
-Caused by:
-  expected a string, but found table at `include[0]` in `[ROOT]/.cargo/config.toml
-"#]],
-    );
+        .build();
+    assert_eq!(gctx.get::<i32>("key1").unwrap(), 1);
+    assert_eq!(gctx.get::<i32>("key2").unwrap(), 2);
 }
 
 #[cargo_test]
@@ -636,7 +617,7 @@ fn table_missing_required_field() {
 could not load Cargo configuration
 
 Caused by:
-  expected a string, but found table at `include[0]` in `[ROOT]/.cargo/config.toml
+  missing field `path` at `include[0]` in `[ROOT]/.cargo/config.toml`
 "#]],
     );
 }