Add support for ternary expression (#81)

Fixes https://github.com/tree-sitter/tree-sitter-bash/issues/64

corpus/statements.txt

@@ -268,6 +268,26 @@ fi
       (command_substitution (command (command_name (word)) (raw_string)))))
     (command (command_name (word)) (word))))
 
+
+=============================
+Test commands with ternary
+=============================
+
+if (( 1 < 2 ? 1 : 2 )); then
+	return 1
+fi
+
+---
+
+(program
+  (if_statement
+    (test_command
+      (ternary_expression
+        (binary_expression (word) (word))
+        (word) (word)))
+    (command
+      (command_name (word)) (word))))
+
 =============================
 Test commands with regexes
 =============================

grammar.js

@@ -353,6 +353,7 @@ module.exports = grammar({
     _expression: $ => choice(
       $._literal,
       $.unary_expression,
+      $.ternary_expression,
       $.binary_expression,
       $.postfix_expression,
       $.parenthesized_expression
@@ -377,6 +378,16 @@ module.exports = grammar({
       )
     )),
 
+    ternary_expression: $ => prec.left(
+      seq(
+        field('condition', $._expression),
+        '?',
+        field('consequence', $._expression),
+        ':',
+        field('alternative', $._expression),
+      )
+    ),
+
     unary_expression: $ => prec.right(seq(
       choice('!', $.test_operator),
       $._expression

src/grammar.json

@@ -1481,6 +1481,10 @@
           "type": "SYMBOL",
           "name": "unary_expression"
         },
+        {
+          "type": "SYMBOL",
+          "name": "ternary_expression"
+        },
         {
           "type": "SYMBOL",
           "name": "binary_expression"
@@ -1632,6 +1636,47 @@
         ]
       }
     },
+    "ternary_expression": {
+      "type": "PREC_LEFT",
+      "value": 0,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "FIELD",
+            "name": "condition",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          },
+          {
+            "type": "STRING",
+            "value": "?"
+          },
+          {
+            "type": "FIELD",
+            "name": "consequence",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          },
+          {
+            "type": "STRING",
+            "value": ":"
+          },
+          {
+            "type": "FIELD",
+            "name": "alternative",
+            "content": {
+              "type": "SYMBOL",
+              "name": "_expression"
+            }
+          }
+        ]
+      }
+    },
     "unary_expression": {
       "type": "PREC_RIGHT",
       "value": 0,

src/node-types.json

@@ -23,6 +23,10 @@
         "type": "postfix_expression",
         "named": true
       },
+      {
+        "type": "ternary_expression",
+        "named": true
+      },
       {
         "type": "unary_expression",
         "named": true
@@ -1101,6 +1105,42 @@
       ]
     }
   },
+  {
+    "type": "ternary_expression",
+    "named": true,
+    "fields": {
+      "alternative": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "_expression",
+            "named": true
+          }
+        ]
+      },
+      "condition": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "_expression",
+            "named": true
+          }
+        ]
+      },
+      "consequence": {
+        "multiple": false,
+        "required": true,
+        "types": [
+          {
+            "type": "_expression",
+            "named": true
+          }
+        ]
+      }
+    }
+  },
   {
     "type": "test_command",
     "named": true,
@@ -1423,6 +1463,10 @@
     "type": ">|",
     "named": false
   },
+  {
+    "type": "?",
+    "named": false
+  },
   {
     "type": "[",
     "named": false