More documentation on the impliedNodeFormat SourceFile field (#49816)

Author: weswigham

src/compiler/types.ts

@@ -3791,6 +3791,12 @@ namespace ts {
          * It is _public_ so that (pre)transformers can set this field,
          * since it switches the builtin `node` module transform. Generally speaking, if unset,
          * the field is treated as though it is `ModuleKind.CommonJS`.
+         *
+         * Note that this field is only set by the module resolution process when
+         * `moduleResolution` is `Node16` or `NodeNext`, which is implied by the `module` setting
+         * of `Node16` or `NodeNext`, respectively, but may be overriden (eg, by a `moduleResolution`
+         * of `node`). If so, this field will be unset and source files will be considered to be
+         * CommonJS-output-format by the node module transformer and type checker, regardless of extension or context.
          */
         impliedNodeFormat?: ModuleKind.ESNext | ModuleKind.CommonJS;
 

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2096,6 +2096,12 @@ declare namespace ts {
          * It is _public_ so that (pre)transformers can set this field,
          * since it switches the builtin `node` module transform. Generally speaking, if unset,
          * the field is treated as though it is `ModuleKind.CommonJS`.
+         *
+         * Note that this field is only set by the module resolution process when
+         * `moduleResolution` is `Node16` or `NodeNext`, which is implied by the `module` setting
+         * of `Node16` or `NodeNext`, respectively, but may be overriden (eg, by a `moduleResolution`
+         * of `node`). If so, this field will be unset and source files will be considered to be
+         * CommonJS-output-format by the node module transformer and type checker, regardless of extension or context.
          */
         impliedNodeFormat?: ModuleKind.ESNext | ModuleKind.CommonJS;
     }

tests/baselines/reference/api/typescript.d.ts

@@ -2096,6 +2096,12 @@ declare namespace ts {
          * It is _public_ so that (pre)transformers can set this field,
          * since it switches the builtin `node` module transform. Generally speaking, if unset,
          * the field is treated as though it is `ModuleKind.CommonJS`.
+         *
+         * Note that this field is only set by the module resolution process when
+         * `moduleResolution` is `Node16` or `NodeNext`, which is implied by the `module` setting
+         * of `Node16` or `NodeNext`, respectively, but may be overriden (eg, by a `moduleResolution`
+         * of `node`). If so, this field will be unset and source files will be considered to be
+         * CommonJS-output-format by the node module transformer and type checker, regardless of extension or context.
          */
         impliedNodeFormat?: ModuleKind.ESNext | ModuleKind.CommonJS;
     }