From 168c29a0fa847b76a3ab93ac25a0e65111836c16 Mon Sep 17 00:00:00 2001
From: Conduitry <git@chor.date>
Date: Thu, 30 Jan 2020 09:25:16 -0500
Subject: [PATCH] disallow simultaneous foo / {foo} / bind:foo (#4343)

* disallow matching attributes/shorthands/bindings (#4325)

* add tests

* update changelog
---
 CHANGELOG.md                                  |  4 +++
 src/compiler/parse/state/tag.ts               | 31 ++++++++++++-------
 .../attribute-unique-binding-error/error.json | 10 ++++++
 .../input.svelte                              |  1 +
 .../error.json                                | 10 ++++++
 .../input.svelte                              |  1 +
 6 files changed, 46 insertions(+), 11 deletions(-)
 create mode 100644 test/parser/samples/attribute-unique-binding-error/error.json
 create mode 100644 test/parser/samples/attribute-unique-binding-error/input.svelte
 create mode 100644 test/parser/samples/attribute-unique-shorthand-error/error.json
 create mode 100644 test/parser/samples/attribute-unique-shorthand-error/input.svelte

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 00ea564045f8..10e23686eaeb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Svelte changelog
 
+## Unreleased
+
+* Disallow attribute/prop names from matching two-way-bound names or `{shorthand}` attribute/prop names ([#4325](https://github.com/sveltejs/svelte/issues/4325))
+
 ## 3.18.1
 
 * Fix code generation error with adjacent inline and block comments ([#4312](https://github.com/sveltejs/svelte/issues/4312))
diff --git a/src/compiler/parse/state/tag.ts b/src/compiler/parse/state/tag.ts
index c7e761afc220..40bb01de9bee 100644
--- a/src/compiler/parse/state/tag.ts
+++ b/src/compiler/parse/state/tag.ts
@@ -288,6 +288,16 @@ function read_tag_name(parser: Parser) {
 function read_attribute(parser: Parser, unique_names: Set<string>) {
 	const start = parser.index;
 
+	function check_unique(name: string) {
+		if (unique_names.has(name)) {
+			parser.error({
+				code: `duplicate-attribute`,
+				message: 'Attributes need to be unique'
+			}, start);
+		}
+		unique_names.add(name);
+	}
+
 	if (parser.eat('{')) {
 		parser.allow_whitespace();
 
@@ -310,6 +320,8 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 			parser.allow_whitespace();
 			parser.eat('}', true);
 
+			check_unique(name);
+
 			return {
 				start,
 				end: parser.index,
@@ -341,17 +353,6 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 	const colon_index = name.indexOf(':');
 	const type = colon_index !== -1 && get_directive_type(name.slice(0, colon_index));
 
-	if (unique_names.has(name)) {
-		parser.error({
-			code: `duplicate-attribute`,
-			message: 'Attributes need to be unique'
-		}, start);
-	}
-
-	if (type !== "EventHandler") {
-		unique_names.add(name);
-	}
-
 	let value: any[] | true = true;
 	if (parser.eat('=')) {
 		parser.allow_whitespace();
@@ -367,6 +368,12 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 	if (type) {
 		const [directive_name, ...modifiers] = name.slice(colon_index + 1).split('|');
 
+		if (type === 'Binding' && directive_name !== 'this') {
+			check_unique(directive_name);
+		} else if (type !== 'EventHandler') {
+			check_unique(name);
+		}
+
 		if (type === 'Ref') {
 			parser.error({
 				code: `invalid-ref-directive`,
@@ -410,6 +417,8 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 		return directive;
 	}
 
+	check_unique(name);
+
 	return {
 		start,
 		end,
diff --git a/test/parser/samples/attribute-unique-binding-error/error.json b/test/parser/samples/attribute-unique-binding-error/error.json
new file mode 100644
index 000000000000..dd145721499e
--- /dev/null
+++ b/test/parser/samples/attribute-unique-binding-error/error.json
@@ -0,0 +1,10 @@
+{
+	"code": "duplicate-attribute",
+	"message": "Attributes need to be unique",
+	"start": {
+		"line": 1,
+		"column": 17,
+		"character": 17
+	},
+	"pos": 17
+}
diff --git a/test/parser/samples/attribute-unique-binding-error/input.svelte b/test/parser/samples/attribute-unique-binding-error/input.svelte
new file mode 100644
index 000000000000..78f854bad629
--- /dev/null
+++ b/test/parser/samples/attribute-unique-binding-error/input.svelte
@@ -0,0 +1 @@
+<Widget foo={42} bind:foo/>
\ No newline at end of file
diff --git a/test/parser/samples/attribute-unique-shorthand-error/error.json b/test/parser/samples/attribute-unique-shorthand-error/error.json
new file mode 100644
index 000000000000..dd145721499e
--- /dev/null
+++ b/test/parser/samples/attribute-unique-shorthand-error/error.json
@@ -0,0 +1,10 @@
+{
+	"code": "duplicate-attribute",
+	"message": "Attributes need to be unique",
+	"start": {
+		"line": 1,
+		"column": 17,
+		"character": 17
+	},
+	"pos": 17
+}
diff --git a/test/parser/samples/attribute-unique-shorthand-error/input.svelte b/test/parser/samples/attribute-unique-shorthand-error/input.svelte
new file mode 100644
index 000000000000..d486eab55852
--- /dev/null
+++ b/test/parser/samples/attribute-unique-shorthand-error/input.svelte
@@ -0,0 +1 @@
+<div title='foo' {title}></div>
\ No newline at end of file