Add regression test for config delimiters

testing/operator-paren-config.toml

@@ -0,0 +1,4 @@
+[[syntax]]
+name = "paren"
+expr_start = "<)"
+expr_end = "(>"

testing/operator-plus-config.toml

@@ -0,0 +1,4 @@
+[[syntax]]
+name = "plus"
+expr_start = "<+"
+expr_end = "+>"

testing/tests/ui/broken-config.rs

@@ -16,4 +16,12 @@ struct DelimClash;
 #[template(source = "", ext = "txt", config = "delim-too-short.toml")]
 struct DelimTooShort;
 
+#[derive(Template)]
+#[template(source = "<+a+> and <+b+>", config = "operator-plus-config.toml", syntax = "plus", ext = "txt")]
+struct PlusOperator;
+
+#[derive(Template)]
+#[template(source = "<)a(> and <)b(>", config = "operator-paren-config.toml", syntax = "paren", ext = "txt")]
+struct ParenOperator;
+
 fn main() {}

testing/tests/ui/broken-config.stderr

@@ -23,3 +23,17 @@ error: delimiters must be at least two characters long. The opening block delimi
    |
 16 | #[template(source = "", ext = "txt", config = "delim-too-short.toml")]
    |                                               ^^^^^^^^^^^^^^^^^^^^^^
+
+error: closing delimiters may not start with operators. The closing expression delimiter ("+>") starts with operator `+`
+        --> testing/operator-plus-config.toml
+  --> tests/ui/broken-config.rs:20:49
+   |
+20 | #[template(source = "<+a+> and <+b+>", config = "operator-plus-config.toml", syntax = "plus", ext = "txt")]
+   |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: closing delimiters may not start with operators. The closing expression delimiter ("(>") starts with operator `(`
+        --> testing/operator-paren-config.toml
+  --> tests/ui/broken-config.rs:24:49
+   |
+24 | #[template(source = "<)a(> and <)b(>", config = "operator-paren-config.toml", syntax = "paren", ext = "txt")]
+   |                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

testing/tests/ui/terminator-operator.stderr

@@ -1,11 +1,11 @@
-error: a closing delimiter must not start with an operator. The expression delimiter (">>") is also an operator
+error: closing delimiters may not start with operators. The closing expression delimiter (">>") starts with operator `>`
         --> testing/issue-128.toml
  --> tests/ui/terminator-operator.rs:4:49
   |
 4 | #[template(source = "<<a>> and <<b>>", config = "issue-128.toml", syntax = "mwe", ext="")]
   |                                                 ^^^^^^^^^^^^^^^^
 
-error: a closing delimiter must not start an with operator. The expression delimiter (">>>") starts with the ">>" operator
+error: closing delimiters may not start with operators. The closing expression delimiter (">>>") starts with operator `>`
         --> testing/issue-128-2.toml
   --> tests/ui/terminator-operator.rs:11:49
    |