Fix language server auto-complete regression in debug build. (#8416)

Fixes this regression:

```slang
struct MyType
{
    // Regression Condition 1: there must be more than one member in the lookup scope.
    float v;
    int getSum() { return 0; }
}

void m(MyType t)
{
    // Regression condition 2: the completion must be in an init expression.
    // Regression condition 3: none of the candidate members can coerce to the expected type.
    // Regression behavior: no completion candidates are shown, because
    // SemanticsVisitor::resolveOverloadedLookup throws an error when there are 0 applicable candidates
    // after type coercion filtering.
    Texture2D x = t.;  // completion request after . here
}
```

The root cause is that we shouldn't be applying candidate filtering on
the candidate list when in completion checking mode.

Closes #8417.

1 files changed, 20 insertions, 0 deletions

diff --git a/tests/language-server/completion-in-initexpr.slang b/tests/language-server/completion-in-initexpr.slang
new file mode 100644
index 000000000..8eec82991
--- /dev/null
+++ b/tests/language-server/completion-in-initexpr.slang
@@ -0,0 +1,20 @@
+//TEST:LANG_SERVER(filecheck=CHECK):
+//COMPLETE:17,21
+struct MyType
+{
+    // Regression Condition 1: there must be more than one member in the lookup scope.
+    float v;
+    int getSum() { return 0; }
+}
+
+void m(MyType t)
+{
+    // Regression condition 2: the completion must be in an init expression.
+    // Regression condition 3: none of the candidate members can coerce to the expected type.
+    // Regression behavior: no completion candidates are shown, because
+    // SemanticsVisitor::resolveOverloadedLookup throws an error when there are 0 applicable candidates
+    // after type coercion filtering.
+    Texture2D x = t.;
+}
+
+// CHECK: getSum