parser: support equals/identical and not variant expressions

phpast/samples/equals.php

@@ -0,0 +1,6 @@
+<?php
+
+$foo == $bar;
+$foo === $bar;
+$foo != $bar;
+$foo !== $bar;

trunk_lexer/src/lexer.rs

@@ -158,7 +158,24 @@ impl Lexer {
         let kind = match char {
             '!' => {
                 self.col += 1;
-                TokenKind::Bang
+
+                if let Some('=') = it.peek() {
+                    self.col += 1;
+
+                    it.next();
+
+                    if let Some('=') = it.peek() {
+                        self.col += 1;
+
+                        it.next();
+
+                        TokenKind::BangDoubleEquals
+                    } else {
+                        TokenKind::BangEquals
+                    }
+                } else {
+                    TokenKind::Bang
+                }
             },
             '&' => {
                 self.col += 1;

trunk_lexer/src/token.rs

@@ -20,6 +20,8 @@ pub enum TokenKind {
     Asterisk,
     Attribute,
     Bang,
+    BangEquals,
+    BangDoubleEquals,
     BoolCast,
     BooleanAnd,
     BooleanOr,

trunk_parser/src/ast.rs

@@ -290,6 +290,10 @@ pub enum InfixOp {
     Mul,
     Concat,
     LessThan,
+    Equals,
+    Identical,
+    NotEquals,
+    NotIdentical,
 }
 
 impl From<TokenKind> for InfixOp {
@@ -301,6 +305,10 @@ impl From<TokenKind> for InfixOp {
             TokenKind::Slash => Self::Div,
             TokenKind::LessThan => Self::LessThan,
             TokenKind::Dot => Self::Concat,
+            TokenKind::DoubleEquals => Self::Equals,
+            TokenKind::TripleEquals => Self::Identical,
+            TokenKind::BangEquals => Self::NotEquals,
+            TokenKind::BangDoubleEquals => Self::NotIdentical,
             _ => unreachable!()
         }
     }

trunk_parser/src/parser/mod.rs

@@ -1122,6 +1122,7 @@ fn infix_binding_power(t: &TokenKind) -> Option<(u8, u8)> {
         TokenKind::Plus | TokenKind::Minus => (11, 12),
         TokenKind::Dot => (11, 11),
         TokenKind::LessThan => (9, 10),
+        TokenKind::DoubleEquals | TokenKind::TripleEquals | TokenKind::BangEquals | TokenKind::BangDoubleEquals => (7, 8),
         TokenKind::Equals => (2, 1),
         _ => return None,
     })
@@ -1262,6 +1263,41 @@ mod tests {
         ]);
     }
 
+    #[test]
+    fn comparisons() {
+        assert_ast("<?php 1 == 1;", &[
+            expr!(Expression::Infix(
+                Box::new(Expression::Int(1)),
+                InfixOp::Equals,
+                Box::new(Expression::Int(1))
+            ))
+        ]);
+
+        assert_ast("<?php 1 === 1;", &[
+            expr!(Expression::Infix(
+                Box::new(Expression::Int(1)),
+                InfixOp::Identical,
+                Box::new(Expression::Int(1))
+            ))
+        ]);
+
+        assert_ast("<?php 1 != 1;", &[
+            expr!(Expression::Infix(
+                Box::new(Expression::Int(1)),
+                InfixOp::NotEquals,
+                Box::new(Expression::Int(1))
+            ))
+        ]);
+
+        assert_ast("<?php 1 !== 1;", &[
+            expr!(Expression::Infix(
+                Box::new(Expression::Int(1)),
+                InfixOp::NotIdentical,
+                Box::new(Expression::Int(1))
+            ))
+        ]);
+    }
+
     #[test]
     fn paren_expression() {
         assert_ast("<?php (1 + 2);", &[