# Finding srcloc for modules in fully-expanded code

**URL:** <https://racket.discourse.group/t/finding-srcloc-for-modules-in-fully-expanded-code/1932>\
**Category:** Questions & Answers\
**Created:** [May 9, 2023, 3:36pm UTC](https://racket.discourse.group/t/finding-srcloc-for-modules-in-fully-expanded-code/1932 "2023-05-09T15:36:17Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![greghendershott](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/greghendershott/32/98_2.png) [@greghendershott](https://racket.discourse.group/u/greghendershott)\
**Post date:** [May 9, 2023, 3:36pm UTC](https://racket.discourse.group/t/finding-srcloc-for-modules-in-fully-expanded-code/1932/1 "2023-05-09T15:36:17Z")

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TL;DR: I can't figure out how to get original srclocs for spliced `module+` forms in fully-expanded code.

* * *

Background: Racket Mode has a run command much like Dr Racket: Run the module for the file, as well as optionally some other submodules like `main` and `test`.

It also has a command to "run the module at point", which could be the outermost file module or any arbitrarily nested submodule. So, you run/enter that module in the REPL (in the sense of `module->namespace`). This can be another handy way to run `test` or `main`, or any submodule. (Sometimes I have `(module+ example __)` as an alternative to commented-out code examples.)

Currently this works by identifying module s-expression surface syntax. So it doesn't work at all for non-sexp langs like rhombus.

* * *

Next: So now I want to make it work "the right way", as with check-syntax, by walking fully-expanded code.

And this is straightforward for things like:

```scheme
#lang racket/base
(module m racket/base
  (module mm racket/base))
(module n racket/base)

```

You can imagine saving in some data structure the `syntax-position` and `syntax-span` of each fully-expanded `module` form, to support a "position-\>module-name" lookup function.

But `module+` is tricky. To support interleaving tests, it has a neat splicing feature. So something like:

```scheme
(module+ test)
(module+ test)
(module+ test)

```

ends up fully expanding to a single `(module* test #f)` form. Unfortunately, its srcloc seems to be only for the _first_ original `(module+ test)` in the source. So if the user had point in one of the others, we couldn't know it was the `test` submodule.

I was excited to notice an `'origin` syntax-property on the `(module* ___)` forms, which is a list of syntax objects, some of which come from the original source. Unfortunately they are syntax objects for just the `module+` identifiers in the original source -- not syntax objects for the complete `(module+__)` original forms.

So... I'll think about it more, but for now I'm stumped.

1. Is there some self-help approach?

2. If not, could a new syntax property be added for the spliced single form, to give a list of syntax objects (or at least srclocs) for all the original pre-spliced forms?

p.s. Although I'm experimenting with this in my "extra analysis" pass of `pdb`, for now, my goal would be to contribute this to drracket/check-syntax.

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<div class="post-metadata">

**Author:** ![greghendershott](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/greghendershott/32/98_2.png) [@greghendershott](https://racket.discourse.group/u/greghendershott)\
**Post date:** [May 9, 2023, 7:05pm UTC](https://racket.discourse.group/t/finding-srcloc-for-modules-in-fully-expanded-code/1932/2 "2023-05-09T19:05:45Z")

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This change to `module+` seems to suffice. "It works", but does it seem correct?

Also not sure about:

The property name, `spliced-module-srcloc`?

The property value, a `srcloc` `struct`; even though I don't think it needs to be preserved (serialized), would a srcloc `vector` still be better?

```diff
modified racket/collects/racket/private/submodule.rkt
@@ -27,7 +27,10 @@
                 (set-box! stxs-box
                           (cons (append (reverse (syntax->list (syntax-local-introduce #'(e ...))))
                                         (car (unbox stxs-box)))
- (cons (syntax-local-introduce stx) (cdr (unbox stxs-box))))))
+ (cons (syntax-property (syntax-local-introduce stx)
+ 'spliced-module-srcloc
+ (syntax-srcloc stx))
+ (cdr (unbox stxs-box))))))
               (syntax/loc stx (begin)))])]
         [else
          (raise-syntax-error #f

```

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<div class="post-metadata">

**Author:** ![greghendershott](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/greghendershott/32/98_2.png) [@greghendershott](https://racket.discourse.group/u/greghendershott)\
**Post date:** [May 10, 2023, 5:25pm UTC](https://racket.discourse.group/t/finding-srcloc-for-modules-in-fully-expanded-code/1932/3 "2023-05-10T17:25:26Z")

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To make things easy in case it's OK as-is, I went ahead and submitted that as [a pull request](https://github.com/racket/racket/pull/4646).