fix(parser): Allow complex expressions on RHS of set statements (#191)

The parser was a little bit too greedy when attempting to detect set
statements, which I should have noticed with the weird workarounds in
that function.  Now that we're _not_ trying to read an entire expression
as the left-hand side of a set statement (e.g.  `foo + bar *= 3`), that
complication can be removed.

Arbitrarily complex expressions are now supported on the right-hand side
of a set statement, e.g. `foo.bar = true and false or 3 > 4`

fixes #156

src/parser/Parser.ts

@@ -632,50 +632,34 @@ export class Parser {
                 );
             }
 
-            let expr = expression();
-
-            let left: Expr.Expression;
-            let operator: Token;
-            let right: Expr.Expression;
-
-            if (expr instanceof Expr.Binary) {
-                // Simple assignments (e.g. `foo.bar = "baz"`) are parsed as binary expressions
-                // because of the ambiguity of the `=` operator without context
-                left = expr.left;
-                operator = expr.token;
-                right = expr.right;
-            } else if (check(...assignmentOperators)) {
-                // Otherwise it appears to be a set statement
-                left = expr;
-                operator = advance();
-                let parsedRhs = expression();
-
-                // De-sugar assignment operators into binary expressions that operate on the
-                // left- and right-hand sides of the operator
-                right = new Expr.Binary(left, operator, parsedRhs);
-            } else {
-                return _expressionStatement();
-            }
-
-
-            // Create a dotted or indexed "set" based on the left-hand side's type
-            if (left instanceof Expr.IndexedGet) {
-                consume("Expected newline or ':' after indexed 'set' statement", Lexeme.Newline, Lexeme.Colon, Lexeme.Eof);
-
-                return new Stmt.IndexedSet(
-                    left.obj,
-                    left.index,
-                    right,
-                    left.closingSquare,
-                );
-            } else if (left instanceof Expr.DottedGet) {
-                consume("Expected newline or ':' after dotted 'set' statement", Lexeme.Newline, Lexeme.Colon, Lexeme.Eof);
+            let expr = call();
+            if (check(...assignmentOperators) && !(expr instanceof Expr.Call)) {
+                let left = expr;
+                let operator = advance();
+                let right = expression();
+
+
+                // Create a dotted or indexed "set" based on the left-hand side's type
+                if (left instanceof Expr.IndexedGet) {
+                    consume("Expected newline or ':' after indexed 'set' statement", Lexeme.Newline, Lexeme.Colon, Lexeme.Eof);
+
+                    return new Stmt.IndexedSet(
+                        left.obj,
+                        left.index,
+                        operator.kind === Lexeme.Equal ? right : new Expr.Binary(left, operator, right),
+                        left.closingSquare,
+                    );
+                } else if (left instanceof Expr.DottedGet) {
+                    consume("Expected newline or ':' after dotted 'set' statement", Lexeme.Newline, Lexeme.Colon, Lexeme.Eof);
 
-                return new Stmt.DottedSet(
-                    left.obj,
-                    left.name,
-                    right,
-                );
+                    return new Stmt.DottedSet(
+                        left.obj,
+                        left.name,
+                        operator.kind === Lexeme.Equal ? right : new Expr.Binary(left, operator, right),
+                    );
+                } else {
+                    return _expressionStatement();
+                }
             } else {
                 return _expressionStatement();
             }

test/e2e/Iterables.test.js

@@ -47,7 +47,10 @@ describe("end to end iterables", () => {
                 "3",
 
                 // modify twoDimensional.secondLayer.level to sanity-check *= and friends
-                "6"
+                "6",
+
+                // add `false` via expression to `empty`
+                "false"
             ]);
         });
     });

test/e2e/resources/associative-arrays.brs

@@ -19,6 +19,10 @@ twoDimensional.secondLayer.thirdLayer = { level: 3 }
 
 print twoDimensional.secondLayer.thirdLayer.level
 
-' modify the top for an as
+' modify the top for a silly example
 twoDimensional.secondLayer.level *= 3
 print twoDimensional.secondLayer.level
+
+' add property to `empty` to be really silly
+empty.isEmpty = oneDimensional.isOneDimensional and false
+print empty.isEmpty

test/parser/expression/Function.test.js

@@ -392,7 +392,7 @@ describe("parser", () => {
         it("allows sub expressions in call arguments", () => {
             const { statements, errors } = parser.parse([
                 identifier("acceptsCallback"),
-                { kind: Lexeme.LeftParen,  text: "(", line: 1 },
+                token(Lexeme.LeftParen, "("),
                 token(Lexeme.Newline, "\\n"),
 
                 token(Lexeme.Function, "function"),

test/parser/statement/Set.test.js

@@ -11,7 +11,7 @@ describe("parser indexed assignment", () => {
     });
 
     describe("dotted", () => {
-        test("assignment", () => {
+        it("assigns anonymous functions", () => {
             let { statements, errors } = parser.parse([
                 identifier("foo"),
                 token(Lexeme.Dot, "."),
@@ -31,6 +31,25 @@ describe("parser indexed assignment", () => {
             expect(statements).toMatchSnapshot();
         });
 
+        it("assigns boolean expressions", () => {
+            let { statements, errors } = parser.parse([
+                identifier("foo"),
+                token(Lexeme.Dot, "."),
+                identifier("bar"),
+                token(Lexeme.Equal, "="),
+                token(Lexeme.True, "true"),
+                token(Lexeme.And, "and"),
+                token(Lexeme.False, "false"),
+                token(Lexeme.Newline, "\\n"),
+                EOF
+            ]);
+
+            expect(errors).toEqual([])
+            expect(statements).toBeDefined();
+            expect(statements).not.toBeNull();
+            expect(statements).toMatchSnapshot();
+        });
+
         test("assignment operator", () => {
            let { statements, errors } = parser.parse([
                identifier("foo"),
@@ -50,7 +69,7 @@ describe("parser indexed assignment", () => {
     });
 
     describe("bracketed", () => {
-        it("assignment", () => {
+        it("assigns anonymous functions", () => {
             let { statements, errors } = parser.parse([
                 identifier("someArray"),
                 token(Lexeme.LeftSquare, "["),
@@ -71,6 +90,26 @@ describe("parser indexed assignment", () => {
             expect(statements).toMatchSnapshot();
         });
 
+        it("assigns boolean expressions", () => {
+            let { statements, errors } = parser.parse([
+                identifier("someArray"),
+                token(Lexeme.LeftSquare, "["),
+                token(Lexeme.Integer, "0", new Int32(0)),
+                token(Lexeme.RightSquare, "]"),
+                token(Lexeme.Equal, "="),
+                token(Lexeme.True, "true"),
+                token(Lexeme.And, "and"),
+                token(Lexeme.False, "false"),
+                token(Lexeme.Newline, "\\n"),
+                EOF
+            ]);
+
+            expect(errors).toEqual([])
+            expect(statements).toBeDefined();
+            expect(statements).not.toBeNull();
+            expect(statements).toMatchSnapshot();
+        });
+
         it("assignment operator", () => {
             let { statements, errors } = parser.parse([
                 identifier("someArray"),