[FIR] Report package usages as a LHS

#KT-59972

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonExpressionCheckers.kt

@@ -162,6 +162,7 @@ object CommonExpressionCheckers : ExpressionCheckers() {
     override val resolvedQualifierCheckers: Set<FirResolvedQualifierChecker>
         get() = setOf(
             FirStandaloneQualifierChecker,
+            FirPackageOnLhsQualifierChecker,
             FirOptInUsageQualifierChecker,
             FirDeprecatedQualifierChecker,
             FirVisibilityQualifierChecker,

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirPackageOnLhsQualifierChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.analysis.checkers.expression
+
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.expressions.FirCallableReferenceAccess
+import org.jetbrains.kotlin.fir.expressions.FirResolvedQualifier
+
+object FirPackageOnLhsQualifierChecker : FirResolvedQualifierChecker() {
+    override fun check(expression: FirResolvedQualifier, context: CheckerContext, reporter: DiagnosticReporter) {
+        // Check that the expression is a package qualifier
+        if (expression.symbol != null) return
+
+        // Left-Hand Side check
+        val lastCallableReferenceAccess = context.callsOrAssignments.lastOrNull() as? FirCallableReferenceAccess
+        val lastGetClass = context.getClassCalls.lastOrNull()
+        if (lastCallableReferenceAccess?.explicitReceiver !== expression && lastGetClass?.argument !== expression) return
+
+        reporter.reportOn(expression.source, FirErrors.EXPRESSION_EXPECTED_PACKAGE_FOUND, context)
+    }
+}

compiler/testData/diagnostics/tests/callableReference/packageInLhs.fir.kt

@@ -4,7 +4,8 @@
 package foo
 
 fun test() {
-    foo::test
+    <!EXPRESSION_EXPECTED_PACKAGE_FOUND!>foo<!>::test
+    <!EXPRESSION_EXPECTED_PACKAGE_FOUND!>foo<!>::class
 }
 
 // FILE: qualifiedName.kt
@@ -12,5 +13,6 @@ fun test() {
 package foo.bar
 
 fun test() {
-    foo.bar::test
+    foo.<!EXPRESSION_EXPECTED_PACKAGE_FOUND!>bar<!>::test
+    foo.<!EXPRESSION_EXPECTED_PACKAGE_FOUND!>bar<!>::class
 }

compiler/testData/diagnostics/tests/callableReference/packageInLhs.kt

@@ -5,6 +5,7 @@ package foo
 
 fun test() {
     <!EXPRESSION_EXPECTED_PACKAGE_FOUND!>foo<!>::<!DEBUG_INFO_MISSING_UNRESOLVED!>test<!>
+    <!EXPRESSION_EXPECTED_PACKAGE_FOUND!>foo<!>::class
 }
 
 // FILE: qualifiedName.kt
@@ -13,4 +14,5 @@ package foo.bar
 
 fun test() {
     foo.<!EXPRESSION_EXPECTED_PACKAGE_FOUND!>bar<!>::<!DEBUG_INFO_MISSING_UNRESOLVED!>test<!>
+    foo.<!EXPRESSION_EXPECTED_PACKAGE_FOUND!>bar<!>::class
 }