Allow defining subtables of tables created via dotted keys (#14)

* Fix the `invalid!` macro

* Rewrite `deserialize_table`

Previously, defining subtables of tables created via dotted keys was not
allowed, even though it is valid according to the spec. For example, the
following valid TOML was incorrectly rejected:
  a.b = 0
  [a.c]

Author: hacrvlq

integ-tests/data/array_within_dotted.toml

@@ -0,0 +1,5 @@
+[fruit]
+apple.color = "red"
+
+[[fruit.apple.seeds]]
+size = 2

integ-tests/data/table_9_invalid.toml

@@ -0,0 +1,9 @@
+[fruit]
+apple.color = "red"
+apple.taste.sweet = true
+
+# [fruit.apple]  # INVALID
+[fruit.apple.taste]  # INVALID
+
+[fruit.apple.texture]  # you can add sub-tables
+smooth = true

integ-tests/data/table_9_reverse_invalid.toml

@@ -0,0 +1,9 @@
+# [fruit.apple]  # INVALID
+[fruit.apple.taste]  # INVALID
+
+[fruit]
+apple.color = "red"
+apple.taste.sweet = true
+
+[fruit.apple.texture]  # you can add sub-tables
+smooth = true

integ-tests/data/table_9_reverse_valid.toml

@@ -0,0 +1,9 @@
+[fruit.apple.texture]  # you can add sub-tables
+smooth = true
+
+[fruit]
+apple.color = "red"
+apple.taste.sweet = true
+
+# [fruit.apple]  # INVALID
+# [fruit.apple.taste]  # INVALID

integ-tests/data/table_9_valid.toml

@@ -0,0 +1,9 @@
+[fruit]
+apple.color = "red"
+apple.taste.sweet = true
+
+# [fruit.apple]  # INVALID
+# [fruit.apple.taste]  # INVALID
+
+[fruit.apple.texture]  # you can add sub-tables
+smooth = true

integ-tests/src/lib.rs

@@ -221,8 +221,8 @@ macro_rules! invalid {
             let toml_str =
                 std::fs::read_to_string(dbg!(concat!("data/", stringify!($name), ".toml")))
                     .expect(concat!("failed to load ", stringify!($name), ".toml"));
-            let error = toml_span::parse(toml_str).unwrap_err();
-            $crate::error_snapshot!($name, error, &toml_str);
+            let error = toml_span::parse(&toml_str).unwrap_err();
+            $crate::error_snapshot!($name, Some(error.to_diagnostic(())), &toml_str);
         }
     };
     ($name:ident, $toml:expr) => {

integ-tests/tests/parser.rs

@@ -49,6 +49,12 @@ name = "Born in the USA"
 "#
 );
 
+valid!(table_9_valid);
+valid!(table_9_reverse_valid);
+invalid!(table_9_invalid);
+invalid!(table_9_reverse_invalid);
+valid!(array_within_dotted);
+
 mod stray_cr {
     use super::invalid;
 

integ-tests/tests/snapshots/parser__array_within_dotted-2.snap

@@ -0,0 +1,54 @@
+---
+source: integ-tests/tests/parser.rs
+expression: spans
+---
+note[string]: root_fruit_apple_color
+  ┌─ array_within_dotted:2:16
+  │
+2 │ apple.color = "red"
+  │                ^^^
+
+note[integer]: root_fruit_apple_seeds_0_size
+  ┌─ array_within_dotted:5:8
+  │
+5 │ size = 2
+  │        ^
+
+note[table]: root_fruit_apple_seeds_0
+  ┌─ array_within_dotted:4:1
+  │  
+4 │ ╭ [[fruit.apple.seeds]]
+5 │ │ size = 2
+  │ ╰────────^
+
+note[array]: root_fruit_apple_seeds
+  ┌─ array_within_dotted:4:1
+  │  
+4 │ ╭ [[fruit.apple.seeds]]
+5 │ │ size = 2
+  │ ╰────────^
+
+note[table]: root_fruit_apple
+  ┌─ array_within_dotted:4:1
+  │  
+4 │ ╭ [[fruit.apple.seeds]]
+5 │ │ size = 2
+  │ ╰────────^
+
+note[table]: root_fruit
+  ┌─ array_within_dotted:1:1
+  │  
+1 │ ╭ [fruit]
+2 │ │ apple.color = "red"
+  │ ╰───────────────────^
+
+note[table]: root
+  ┌─ array_within_dotted:1:1
+  │  
+1 │ ╭ [fruit]
+2 │ │ apple.color = "red"
+3 │ │ 
+4 │ │ [[fruit.apple.seeds]]
+5 │ │ size = 2
+6 │ │ 
+  │ ╰^

integ-tests/tests/snapshots/parser__array_within_dotted.snap

@@ -0,0 +1,16 @@
+---
+source: integ-tests/tests/parser.rs
+expression: valid_toml
+---
+{
+  "fruit": {
+    "apple": {
+      "color": "red",
+      "seeds": [
+        {
+          "size": 2
+        }
+      ]
+    }
+  }
+}

integ-tests/tests/snapshots/parser__table_9_invalid.snap

@@ -0,0 +1,12 @@
+---
+source: integ-tests/tests/parser.rs
+expression: error
+---
+error[duplicate-key]: 
+  ┌─ table_9_invalid:6:14
+  │
+3 │ apple.taste.sweet = true
+  │       ----- first key instance
+  ·
+6 │ [fruit.apple.taste]  # INVALID
+  │              ^^^^^ duplicate key