Retain synthetic comments on classes and their properties.

src/compiler/transformers/ts.ts

@@ -1245,6 +1245,7 @@ namespace ts {
                 const statement = createExpressionStatement(transformInitializedProperty(property, receiver));
                 setSourceMapRange(statement, moveRangePastModifiers(property));
                 setCommentRange(statement, property);
+                setOriginalNode(statement, property);
                 statements.push(statement);
             }
         }
@@ -1262,6 +1263,7 @@ namespace ts {
                 startOnNewLine(expression);
                 setSourceMapRange(expression, moveRangePastModifiers(property));
                 setCommentRange(expression, property);
+                setOriginalNode(expression, property);
                 expressions.push(expression);
             }
 

src/testRunner/unittests/transform.ts

@@ -334,6 +334,29 @@ export {Value};
                         }
                     }).outputText;
         });
+
+        // https://github.com/Microsoft/TypeScript/issues/17594
+        testBaseline("transformAddCommentToProperties", () => {
+            return transpileModule(`
+// class comment.
+class Clazz {
+    // original comment 1.
+    static staticProp: number = 1;
+    // original comment 2.
+    instanceProp: number = 2;
+    // original comment 3.
+    constructor(readonly field = 1) {}
+}
+`, {
+                        transformers: {
+                            before: [addSyntheticComment(n => isPropertyDeclaration(n) || isParameterPropertyDeclaration(n) || isClassDeclaration(n) || isConstructorDeclaration(n))],
+                        },
+                        compilerOptions: {
+                            target: ScriptTarget.ES2015,
+                            newLine: NewLineKind.CarriageReturnLineFeed,
+                        }
+                    }).outputText;
+        });
     });
 }
 

tests/baselines/reference/transformApi/transformsCorrectly.transformAddCommentToClassProp.js

@@ -0,0 +1,7 @@
+class X {
+    constructor() {
+        // new comment!
+        // original comment.
+        this.foo = 1;
+    }
+}

tests/baselines/reference/transformApi/transformsCorrectly.transformAddCommentToProperties.js

@@ -0,0 +1,12 @@
+/*comment*/
+class Clazz {
+    /*comment*/
+    constructor(/*comment*/
+    field = 1) {
+        this.field = field;
+        /*comment*/
+        this.instanceProp = 2;
+    }
+}
+/*comment*/
+Clazz.staticProp = 1;