unikernel/duniverse/ppxlib/test/driver/source-quotation-in-errors/dune

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+(executable
+ (name raising_driver)
+ (modules raising_driver)
+ (libraries ppxlib))
+
+(executable
+ (name identity_driver)
+ (modules identity_driver)
+ (libraries ppxlib))
+
+(cram
+ (package ppxlib)
+ (enabled_if
+  (>= %{ocaml_version} "4.08.0"))
+ (deps raising_driver.exe identity_driver.exe))

unikernel/duniverse/ppxlib/test/driver/source-quotation-in-errors/identity_driver.ml

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+let () = Ppxlib.Driver.standalone ()

unikernel/duniverse/ppxlib/test/driver/source-quotation-in-errors/raising_driver.ml

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+open Ppxlib
+
+let rules =
+  [
+    Extension.V3.declare "raise" Extension.Context.expression
+      Ast_pattern.(pstr nil)
+      (fun ~ctxt ->
+        let loc = Expansion_context.Extension.extension_point_loc ctxt in
+        Location.raise_errorf ~loc "An exception, raise be!")
+    |> Context_free.Rule.extension;
+  ]
+
+let () = Driver.V2.register_transformation ~rules "raise"
+let () = Driver.standalone ()

unikernel/duniverse/ppxlib/test/driver/source-quotation-in-errors/run.t

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+When the ppxlib driver reports an error by itself, source quotation should work
+properly.
+
+We start off by explicitly setting the error reporting style to contextual to
+ensure source quotation is enabled:
+
+  $ export OCAML_ERROR_STYLE=contextual
+
+Here we have a driver compiled with a single rule that will raise a located
+exception for every "[%raise]" extension point.
+
+We need an input file:
+
+  $ cat > file.ml << EOF
+  > let x = [%raise]
+  > EOF
+
+When running the driver on this file, it should report the error and show
+the relevant quoted source:
+
+  $ ./raising_driver.exe -impl file.ml
+  File "file.ml", line 1, characters 8-16:
+  1 | let x = [%raise]
+              ^^^^^^^^
+  Error: An exception, raise be!
+  [1]
+
+This should also work when the input is a binary AST as the file contains the name
+of the original source file. Our driver should be able to properly set the input
+lexbuf and get the source quotation to work, assuming the information in the binary
+AST file is correct.
+
+Here we use an identity driver to generate the binary AST for our .ml file above:
+
+  $ ./identity_driver.exe -impl file.ml -dump-ast -o file.pp.ml 
+
+We then call our raising driver on the binary AST, it should be able to report the
+error with source quotation:
+
+  $ ./raising_driver.exe -impl file.pp.ml
+  File "file.ml", line 1, characters 8-16:
+  1 | let x = [%raise]
+              ^^^^^^^^
+  Error: An exception, raise be!
+  [1]