add constant string concatenation (#126)

Author: giacomocavalieri

grammar.js

@@ -131,7 +131,8 @@ module.exports = grammar({
         alias($._constant_bit_string, $.bit_string),
         alias($.constant_record, $.record),
         $.identifier,
-        alias($.constant_field_access, $.field_access)
+        alias($.constant_field_access, $.field_access),
+        alias($.constant_binary_expression, $.binary_expression)
       ),
     constant_tuple: ($) =>
       seq("#", "(", optional(series_of($._constant_value, ",")), ")"),
@@ -159,6 +160,8 @@ module.exports = grammar({
         ),
         seq(field("label", $.label), ":")
       ),
+    constant_binary_expression: ($) =>
+      choice(binaryExpr(prec.left, 7, "<>", $._constant_value)),
     // This rule exists to parse remote function references which are generally
     // indistinguishable from field accesses and so share an AST node.
     constant_field_access: ($) =>

test/corpus/constants.txt

@@ -463,3 +463,24 @@ const b = Wibble(arg:, arg:)
           (label))
         (argument
           (label))))))
+
+================================================================================
+String concatenation constants
+================================================================================
+
+const name = "Jak"
+const string = "hello, " <> name <> "!"
+
+--------------------------------------------------------------------------------
+
+(source_file
+  (constant
+    (identifier)
+    (string (quoted_content)))
+  (constant
+    (identifier)
+    (binary_expression
+      (binary_expression
+        (string (quoted_content))
+        (identifier))
+      (string (quoted_content)))))

test/highlight/constants.gleam

@@ -8,3 +8,8 @@ const s = "Hello, \e\t\n"
 //                 ^ warning
 //                   ^ string.escape
 //                    ^ string.escape
+
+const s = "Hello, " <> "World!"
+//              ^ string
+//                  ^ operator
+//                       ^ string