[ddc] Fix sourcemap for field initializers

New source locations were added for field initializers to support
upcoming primary constructor work.
See: https://dart-review.googlesource.com/c/sdk/+/468780

This change ensures the initializer assignment statements we add to
the constructor body are fully mapped.

Without this change the new initializer assignment wasn't getting a
mapping so it continued from whatever appeared before it.

Change-Id: Id6ba0619e49e4a517ea36ffa728cf0c1502a14e8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/469300
Auto-Submit: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -2375,12 +2375,8 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
           : _getSymbol(virtualField);
       var jsInit = _visitInitializer(initializer, f.annotations);
       body.add(
-        jsInit
-            .toAssignExpression(
-              js.call('this.#', [access])
-                ..sourceInformation = _nodeStart(hoverInfo),
-            )
-            .toStatement(),
+        jsInit.toAssignExpression(js.call('this.#', [access])).toStatement()
+          ..sourceInformation = _nodeStart(hoverInfo),
       );
     }
 

pkg/dev_compiler/lib/src/kernel/compiler_new.dart

@@ -2665,16 +2665,15 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
     return access;
   }
 
-  js_ast.Expression _emitFieldInit(
+  js_ast.Statement _emitFieldInit(
     Field f,
     Expression? initializer,
     TreeNode hoverInfo,
   ) {
     var access = _emitFieldValueAccessor(f);
     var jsInit = _visitInitializer(initializer, f.annotations);
-    return jsInit.toAssignExpression(
-      js.call('this.#', [access])..sourceInformation = _nodeStart(hoverInfo),
-    );
+    return jsInit.toAssignExpression(js.call('this.#', [access])).toStatement()
+      ..sourceInformation = _nodeStart(hoverInfo);
   }
 
   /// Initialize fields. They follow the sequence:
@@ -2700,7 +2699,7 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
         continue;
       }
       _staticTypeContext.enterMember(f);
-      body.add(_emitFieldInit(f, init, f).toStatement());
+      body.add(_emitFieldInit(f, init, f));
       _staticTypeContext.leaveMember(f);
     }
 
@@ -2708,7 +2707,7 @@ class LibraryCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
     if (ctor != null) {
       for (var init in ctor.initializers) {
         if (init is FieldInitializer) {
-          body.add(_emitFieldInit(init.field, init.value, init).toStatement());
+          body.add(_emitFieldInit(init.field, init.value, init));
         } else if (init is LocalInitializer) {
           body.add(visitVariableDeclaration(init.variable));
         } else if (init is AssertInitializer) {