NNBD i13n: Add line numbers to a few messages

fixes #38920

Change-Id: I6656a2e47901cbe66ccbd040d3d2fe6913f7031a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121867
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

pkg/analysis_server/lib/src/edit/nnbd_migration/info_builder.dart

@@ -114,7 +114,7 @@ class InfoBuilder {
 
     /// If the [node] is the return expression for a function body, return the
     /// function body. Otherwise return `null`.
-    AstNode findFunctionBody() {
+    FunctionBody findFunctionBody() {
       if (parent is ExpressionFunctionBody) {
         return parent;
       } else {
@@ -126,16 +126,18 @@ class InfoBuilder {
       }
     }
 
-    AstNode functionBody = findFunctionBody();
+    FunctionBody functionBody = findFunctionBody();
     if (functionBody != null) {
+      CompilationUnit unit = node.thisOrAncestorOfType<CompilationUnit>();
+      int lineNumber = unit.lineInfo.getLocation(node.offset).lineNumber;
       AstNode function = functionBody.parent;
       if (function is MethodDeclaration) {
         if (function.isGetter) {
-          return "This getter returns a nullable value";
+          return "This getter returns a nullable value on line $lineNumber";
         }
-        return "This method returns a nullable value";
+        return "This method returns a nullable value on line $lineNumber";
       }
-      return "This function returns a nullable value";
+      return "This function returns a nullable value on line $lineNumber";
     } else if (parent is VariableDeclaration) {
       AstNode grandparent = parent.parent?.parent;
       if (grandparent is FieldDeclaration) {
@@ -198,7 +200,8 @@ class InfoBuilder {
           CompilationUnit unit = type.thisOrAncestorOfType<CompilationUnit>();
           target = _targetForNode(unit.declaredElement.source.fullName, type);
           return RegionDetail(
-              "The corresponding parameter in the overridden method is nullable",
+              "The corresponding parameter in the overridden method is "
+              "nullable",
               target);
           // TODO(srawlins): Also, this could be where a return type in an
           //  overridden method is made nullable because an overriding method

pkg/analysis_server/test/src/edit/nnbd_migration/info_builder_test.dart

@@ -137,7 +137,7 @@ String? g() => 1 == 2 ? "Hello" : null;
     assertRegion(
         region: regions[0],
         offset: 6,
-        details: ["This function returns a nullable value"]);
+        details: ["This function returns a nullable value on line 1"]);
     assertDetail(detail: regions[0].details[0], offset: 11, length: 2);
   }
 
@@ -516,7 +516,7 @@ String? g() {
     assertRegion(
         region: regions[0],
         offset: 6,
-        details: ["This function returns a nullable value"]);
+        details: ["This function returns a nullable value on line 3"]);
     assertInTargets(targets: unit.targets, offset: 40, length: 6); // "return"
   }
 
@@ -540,7 +540,7 @@ String? g() {
     assertRegion(
         region: regions[0],
         offset: 6,
-        details: ["This function returns a nullable value"]);
+        details: ["This function returns a nullable value on line 2"]);
     assertDetail(detail: regions[0].details[0], offset: 15, length: 6);
   }
 
@@ -566,7 +566,7 @@ int? f() => _f;
     assertRegion(
         region: regions[1],
         offset: 19,
-        details: ["This function returns a nullable value"]);
+        details: ["This function returns a nullable value on line 2"]);
   }
 
   test_returnType_getter_block() async {
@@ -599,7 +599,7 @@ class A {
     assertRegion(
         region: regions[1],
         offset: 33,
-        details: ["This getter returns a nullable value"]);
+        details: ["This getter returns a nullable value on line 4"]);
   }
 
   test_returnType_getter_expression() async {
@@ -628,7 +628,7 @@ class A {
     assertRegion(
         region: regions[1],
         offset: 33,
-        details: ["This getter returns a nullable value"]);
+        details: ["This getter returns a nullable value on line 3"]);
   }
 
   test_topLevelVariable() async {