Change map-capacity-counting part of json_internal! macro to not report errors.

Since these errors are already reported by the part of the macro that actually parses the map,
it is unnecessary to report them twice, so the capacity-counting part can just return 0 if
it encounters an error.

Author: zachs18

src/macros.rs

@@ -254,9 +254,11 @@ macro_rules! json_internal {
         1 + json_internal!(@object_capacity () ($($rest)*) ($($rest)*))
     };
 
-    // Current entry followed by unexpected token.
+    // Current entry followed by unexpected token. The part that parses the values
+    // will trigger a reasonable error message; here, we just return 0
+    // so that there is not a duplicated error message.
     (@object_capacity entry $unexpected:tt $($rest:tt)*) => {
-        json_unexpected!($unexpected)
+        0
     };
 
     // Insert the last entry without trailing comma.
@@ -299,29 +301,32 @@ macro_rules! json_internal {
         json_internal!(@object_capacity entry)
     };
 
-    // Missing value for last entry. Trigger a reasonable error message.
+    // Missing value for last entry. The part that parses the values
+    // will trigger a reasonable error message; here, we just return 0
+    // so that there is not a duplicated error message.
     (@object_capacity ($($key:tt)+) (:) $copy:tt) => {
-        // "unexpected end of macro invocation"
-        json_internal!()
+        0
     };
 
-    // Missing colon and value for last entry. Trigger a reasonable error
-    // message.
+    // Missing colon and value for last entry. The part that parses the values
+    // will trigger a reasonable error message; here, we just return 0
+    // so that there is not a duplicated error message.
     (@object_capacity ($($key:tt)+) () $copy:tt) => {
-        // "unexpected end of macro invocation"
-        json_internal!()
+        0
     };
 
-    // Misplaced colon. Trigger a reasonable error message.
+    // Misplaced colon. The part that parses the values
+    // will trigger a reasonable error message; here, we just return 0
+    // so that there is not a duplicated error message.
     (@object_capacity () (: $($rest:tt)*) ($colon:tt $($copy:tt)*)) => {
-        // Takes no arguments so "no rules expected the token `:`".
-        json_unexpected!($colon)
+        0
     };
 
-    // Found a comma inside a key. Trigger a reasonable error message.
+    // Found a comma inside a key. The part that parses the values
+    // will trigger a reasonable error message; here, we just return 0
+    // so that there is not a duplicated error message.
     (@object_capacity ($($key:tt)*) (, $($rest:tt)*) ($comma:tt $($copy:tt)*)) => {
-        // Takes no arguments so "no rules expected the token `,`".
-        json_unexpected!($comma)
+        0
     };
 
     // Key is fully parenthesized. This is not necessary for counting capacity
@@ -331,8 +336,10 @@ macro_rules! json_internal {
     // };
 
     // Refuse to absorb colon token into key expression.
+    // The part that parses the values will trigger a reasonable error message;
+    // here, we just return 0 so that there is not a duplicated error message.
     (@object_capacity ($($key:tt)*) (: $($unexpected:tt)+) $copy:tt) => {
-        json_expect_expr_comma!($($unexpected)+)
+        0
     };
 
     // Munch a token into the current key.

tests/ui/missing_colon.stderr

@@ -5,11 +5,3 @@ error: unexpected end of macro invocation
   |     ^^^^^^^^^^^^^^ missing tokens in macro arguments
   |
   = note: this error originates in the macro `json_internal` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: unexpected end of macro invocation
- --> tests/ui/missing_colon.rs:4:5
-  |
-4 |     json!({ "a" });
-  |     ^^^^^^^^^^^^^^ missing tokens in macro arguments
-  |
-  = note: this error originates in the macro `json_internal` (in Nightly builds, run with -Z macro-backtrace for more info)

tests/ui/missing_value.stderr

@@ -5,11 +5,3 @@ error: unexpected end of macro invocation
   |     ^^^^^^^^^^^^^^^^ missing tokens in macro arguments
   |
   = note: this error originates in the macro `json_internal` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: unexpected end of macro invocation
- --> tests/ui/missing_value.rs:4:5
-  |
-4 |     json!({ "a" : });
-  |     ^^^^^^^^^^^^^^^^ missing tokens in macro arguments
-  |
-  = note: this error originates in the macro `json_internal` (in Nightly builds, run with -Z macro-backtrace for more info)