Fix incorrect diagnostic message when reserved keyword is used in module import

compiler/ballerina-lang/src/main/java/org/wso2/ballerinalang/compiler/parser/BLangNodeBuilder.java

@@ -729,7 +729,23 @@ public BLangNode transform(ImportDeclarationNode importDeclaration) {
         List<BLangIdentifier> pkgNameComps = new ArrayList<>();
         NodeList<IdentifierToken> names = importDeclaration.moduleName();
         Location position = getPosition(importDeclaration);
-        names.forEach(name -> pkgNameComps.add(this.createIdentifier(getPosition(name), name.text())));
+        names.forEach(name -> {
+            // If the token is missing (e.g. a reserved keyword like 'client' was used
+            // without the '^' escape), the parser synthesises a MISSING identifier and
+            // places the original keyword as a leading invalid-token minutiae.
+            // Recover that keyword text so that error messages like
+            // "cannot resolve module 'ballerinax/client.config'" are correct.
+            if (name.isMissing()) {
+                List<Token> leadingInvalid = name.leadingInvalidTokens();
+                String originalValue = name.text(); // empty string for missing tokens
+                if (!leadingInvalid.isEmpty()) {
+                    originalValue = leadingInvalid.get(0).text();
+                }
+                pkgNameComps.add(this.createIdentifier(getPosition(name), "", originalValue));
+            } else {
+                pkgNameComps.add(this.createIdentifier(getPosition(name), name.text()));
+            }
+        });
 
         BLangImportPackage importDcl = (BLangImportPackage) TreeBuilder.createImportPackageNode();
         importDcl.pos = position;

compiler/ballerina-lang/src/main/java/org/wso2/ballerinalang/compiler/tree/BLangImportPackage.java

@@ -134,7 +134,7 @@ public String toString() {
     public String getQualifiedPackageName() {
         String orgName = this.orgName.toString();
         String pkgName = String.join(".", pkgNameComps.stream()
-                .map(id -> id.value)
+                .map(id -> id.value.isEmpty() && id.originalValue != null ? id.originalValue : id.value)
                 .toList());
 
         String versionStr = (this.version.value != null) ? this.version.value : "";

tests/jballerina-unit-test/src/test/java/org/ballerinalang/test/imports/ImportsNegativeTests.java

@@ -56,4 +56,18 @@ public void testInvalidAutoImports() {
         validateError(result, index++, "unknown type 'CallStackElement'", 51, 30);
         assertEquals(result.getErrorCount(), index);
     }
+
+    @Test(description = "Test diagnostic message for reserved keyword in module import path")
+    public void testReservedKeywordInModuleImportDiagnostic() {
+        CompileResult result = BCompileUtil.compile("test-src/imports/ReservedKeywordImportTestProject");
+        int index = 0;
+        // 'client' is a reserved keyword; the diagnostic must include it in the module path,
+        // i.e. "ballerinax/client.config", not "ballerinax/.config" (regression for #44509/#44519).
+        // Diagnostics are ordered by source position; the import declaration starts at col 1,
+        // so the module-resolution error precedes the parser errors at col 19.
+        validateError(result, index++, "cannot resolve module 'ballerinax/client.config as config'", 5, 1);
+        validateError(result, index++, "invalid token 'client'", 5, 19);
+        validateError(result, index++, "missing identifier", 5, 25);
+        assertEquals(result.getErrorCount(), index);
+    }
 }

tests/jballerina-unit-test/src/test/resources/test-src/imports/ReservedKeywordImportTestProject/Ballerina.toml

@@ -0,0 +1,4 @@
+[package]
+org = "testorg"
+name = "reservedkeywordimport"
+version = "1.0.0"

tests/jballerina-unit-test/src/test/resources/test-src/imports/ReservedKeywordImportTestProject/reserved-keyword-import-negative.bal

@@ -0,0 +1,5 @@
+// Test: using a reserved keyword (client) in a module import path without '^' escape
+// should produce a diagnostic that includes the keyword in the module path,
+// i.e. "cannot resolve module 'ballerinax/client.config as config'"
+// NOT "cannot resolve module 'ballerinax/.config as config'"
+import ballerinax/client.config;