From 1a721e5916bb71639f8fcc2cdffe3e99988ff578 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Mon, 12 Feb 2024 19:31:10 +0100
Subject: [PATCH] fix: only throw bind error when not passing a value (#10090)
Relax the runtime error to only throw when you're passing a binding with an undefined value. This makes it possible to provide components in a way that can be used more flexibly while keeping the error to guard against the case that we want to avoid: a default value propagation up.
---
.changeset/big-geese-act.md | 5 +++++
packages/svelte/src/internal/client/runtime.js | 18 +++++++++++-------
.../samples/props-bound-fallback/_config.js | 2 +-
3 files changed, 17 insertions(+), 8 deletions(-)
create mode 100644 .changeset/big-geese-act.md
diff --git a/.changeset/big-geese-act.md b/.changeset/big-geese-act.md
new file mode 100644
index 0000000000..08e1e29d15
--- /dev/null
+++ b/.changeset/big-geese-act.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: only throw bind error when not passing a value
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 21abccf38e..1fe72efa41 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1567,16 +1567,20 @@ export function is_store(val) {
export function prop(props, key, flags, initial) {
var immutable = (flags & PROPS_IS_IMMUTABLE) !== 0;
var runes = (flags & PROPS_IS_RUNES) !== 0;
-
- var setter = get_descriptor(props, key)?.set;
- if (DEV && setter && runes && initial !== undefined) {
- // TODO consolidate all these random runtime errors
- throw new Error('Cannot use fallback values with bind:');
- }
-
var prop_value = /** @type {V} */ (props[key]);
+ var setter = get_descriptor(props, key)?.set;
if (prop_value === undefined && initial !== undefined) {
+ if (setter && runes) {
+ // TODO consolidate all these random runtime errors
+ throw new Error(
+ 'ERR_SVELTE_BINDING_FALLBACK' +
+ (DEV
+ ? `: Cannot pass undefined to bind:${key} because the property contains a fallback value. Pass a different value than undefined to ${key}.`
+ : '')
+ );
+ }
+
// @ts-expect-error would need a cumbersome method overload to type this
if ((flags & PROPS_IS_LAZY_INITIAL) !== 0) initial = initial();
diff --git a/packages/svelte/tests/runtime-runes/samples/props-bound-fallback/_config.js b/packages/svelte/tests/runtime-runes/samples/props-bound-fallback/_config.js
index 6dc700cee5..f382120e88 100644
--- a/packages/svelte/tests/runtime-runes/samples/props-bound-fallback/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/props-bound-fallback/_config.js
@@ -14,5 +14,5 @@ export default test({
assert.htmlEqual(target.innerHTML, `1`);
},
- error: `Cannot use fallback values with bind:`
+ error: `ERR_SVELTE_BINDING_FALLBACK: Cannot pass undefined to bind:count because the property contains a fallback value. Pass a different value than undefined to count.`
});