feat: TypeScript 5.4 support for svelte-check (#2313)

* bump ts to 5.4.2

* assign to bound variable for ts 5.4 to widen to control flow

* format

* oops this doesn't work in 5.3

* revert bumping but keeps compatibility fixes

* lock

* Update packages/svelte2tsx/src/htmlxtojsx_v2/nodes/Binding.ts

Author: jasonlyu123

packages/language-server/src/plugins/typescript/features/DiagnosticsProvider.ts

@@ -543,11 +543,17 @@ function expectedTransitionThirdArgument(
         return false;
     }
 
-    const callExpression = findNodeAtSpan(
-        node,
-        { start: node.getStart(), length: node.getWidth() },
-        ts.isCallExpression
-    );
+    // in TypeScript 5.4 the error is on the function name
+    // in earlier versions it's on the whole call expression
+    const callExpression =
+        ts.isIdentifier(node) && ts.isCallExpression(node.parent)
+            ? node.parent
+            : findNodeAtSpan(
+                  node,
+                  { start: node.getStart(), length: node.getWidth() },
+                  ts.isCallExpression
+              );
+
     const signature =
         callExpression && lang.getProgram()?.getTypeChecker().getResolvedSignature(callExpression);
 

packages/language-server/src/plugins/typescript/module-loader.ts

@@ -102,7 +102,8 @@ class ImpliedNodeFormatResolver {
         let mode = undefined;
         if (sourceFile) {
             this.cacheImpliedNodeFormat(sourceFile, compilerOptions);
-            mode = ts.getModeForResolutionAtIndex(sourceFile, importIdxInFile);
+            // @ts-expect-error remove when bumping to TS 5.4
+            mode = ts.getModeForResolutionAtIndex(sourceFile, importIdxInFile, compilerOptions);
         }
         return mode;
     }

packages/language-server/test/plugins/typescript/features/diagnostics/fixtures/bind-union/Component.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+    export let value: 'foo' | 'bar';
+</script>
+
+<button on:click={() => value = 'foo'}>foo</button>

packages/language-server/test/plugins/typescript/features/diagnostics/fixtures/bind-union/expectedv2.json

@@ -0,0 +1 @@
+[]

packages/language-server/test/plugins/typescript/features/diagnostics/fixtures/bind-union/input.svelte

@@ -0,0 +1,18 @@
+<script lang="ts">
+    import Component from './Component.svelte';
+
+    let checked = false;
+    let value: 'foo' | 'bar' = 'foo';
+</script>
+
+<input type="checkbox" bind:checked>
+
+{#if checked === true}
+    checked
+{/if}
+
+{#if value === 'bar'}
+    bar
+{/if}
+
+<Component bind:value></Component>

packages/svelte2tsx/src/htmlxtojsx_v2/nodes/Binding.ts

@@ -94,6 +94,12 @@ export function handleBinding(
         return;
     }
 
+    // add reassignment to force TS to widen the type of the declaration (in case it's never reassigned anywhere else)
+    const expressionStr = str.original.substring(attr.expression.start, getEnd(attr.expression));
+    element.appendToStartEnd([
+        surroundWithIgnoreComments(`() => ${expressionStr} = __sveltets_2_any(null);`)
+    ]);
+
     // other bindings which are transformed to normal attributes/props
     const isShorthand = attr.expression.start === attr.start + 'bind:'.length;
     const name: TransformationArray =