filter out CompileError::UnknownVariable errors when CONTRACT_ID …

…isn't injected into namespace (FuelLabs#4727)

## Description
When `CONTRACT_ID` is used in a test, the compiler returns
`CompileError::UnknownVariable` to LSP as `CONTRACT_ID` is only injected
into the namespace during building and not checking. As such, we are
filtering out these warnings in the language server so they do not
appear to the end user.

closes FuelLabs/sway-vscode-plugin#154

forc-pkg/src/pkg.rs

@@ -2586,16 +2586,29 @@ pub fn check(
     let compiled_contract_deps = HashMap::new();
 
     let mut results = vec![];
-    for &node in plan.compilation_order.iter() {
+    for (idx, &node) in plan.compilation_order.iter().enumerate() {
         let pkg = &plan.graph[node];
         let manifest = &plan.manifest_map()[&pkg.id()];
+
+        // This is necessary because `CONTRACT_ID` is a special constant that's injected into the
+        // compiler's namespace. Although we only know the contract id during building, we are
+        // inserting a dummy value here to avoid false error signals being reported in LSP.
+        // We only do this for the last node in the compilation order because previous nodes
+        // are dependencies.
+        //
+        // See this github issue for more context: https://github.com/FuelLabs/sway-vscode-plugin/issues/154
+        const DUMMY_CONTRACT_ID: &str =
+            "0x0000000000000000000000000000000000000000000000000000000000000000";
+        let contract_id_value =
+            (idx == plan.compilation_order.len() - 1).then(|| DUMMY_CONTRACT_ID.to_string());
+
         let dep_namespace = dependency_namespace(
             &lib_namespace_map,
             &compiled_contract_deps,
             &plan.graph,
             node,
             engines,
-            None,
+            contract_id_value,
         )
         .expect("failed to create dependency namespace");