fix(inspections): fix unused inspection for _ names (#107)

Fixes #80

Author: i582

server/src/e2e/suite/testcases/inspection/UnusedParameterInspection.test

@@ -4,7 +4,15 @@ Unused parameter inspection
 fun foo(param: Int) {
 }
 ------------------------------------------------------------------------
-3 0:8 to 0:13 Parameter 'param: Int' is never used (tact)
+3 0:8 to 0:13 Parameter 'param' is never used (tact)
+
+========================================================================
+Unused _ parameter inspection
+========================================================================
+fun foo(_: Int) {
+}
+------------------------------------------------------------------------
+no issues
 
 ========================================================================
 Used parameter
@@ -34,9 +42,9 @@ Multiple unused parameters
 fun foo(param: Int, other: String, isTrue: Bool) {
 }
 ------------------------------------------------------------------------
-3 0:8 to 0:13 Parameter 'param: Int' is never used (tact)
-3 0:20 to 0:25 Parameter 'other: String' is never used (tact)
-3 0:35 to 0:41 Parameter 'isTrue: Bool' is never used (tact)
+3 0:8 to 0:13 Parameter 'param' is never used (tact)
+3 0:20 to 0:25 Parameter 'other' is never used (tact)
+3 0:35 to 0:41 Parameter 'isTrue' is never used (tact)
 
 ========================================================================
 Unused parameter inspection in abstract function

server/src/e2e/suite/testcases/inspection/UnusedVariableInspection.test

@@ -7,6 +7,15 @@ fun foo() {
 ------------------------------------------------------------------------
 3 1:8 to 1:9 Variable 'x' is never used (tact)
 
+========================================================================
+Unused _ variable inspection
+========================================================================
+fun foo() {
+    let _ = 1;
+}
+------------------------------------------------------------------------
+no issues
+
 ========================================================================
 Used variable
 ========================================================================

server/src/inspections/UnusedInspection.ts

@@ -15,7 +15,7 @@ export abstract class UnusedInspection {
     protected abstract checkFile(file: File, diagnostics: lsp.Diagnostic[]): void
 
     protected checkUnused(
-        node: SyntaxNode,
+        node: SyntaxNode | null,
         file: File,
         diagnostics: lsp.Diagnostic[],
         options: {
@@ -26,6 +26,8 @@ export abstract class UnusedInspection {
             skipIf?: () => boolean
         },
     ) {
+        if (!node || node.text === "_") return
+
         const references = new Referent(node, file).findReferences()
         if (references.length === 0) {
             const range = asLspRange(options.rangeNode ?? node)

server/src/inspections/UnusedParameterInspection.ts

@@ -30,7 +30,7 @@ export class UnusedParameterInspection extends UnusedInspection {
             const nameIdent = param.nameIdentifier()
             if (!nameIdent) return
 
-            this.checkUnused(param.node, fun.file, diagnostics, {
+            this.checkUnused(param.nameIdentifier(), fun.file, diagnostics, {
                 kind: "Parameter",
                 code: "unused-parameter",
                 rangeNode: nameIdent,