unikernel/duniverse/ppxlib/test/driver/keywords-option/run.t

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+This test can only work with OCaml 5.3 or higher.
+
+OCaml 5.3 introduced the new `effect` keyword. To allow old code to compile
+under 5.3 it also introduced a `-keyword=version+list` CLI option, allowing one to
+override the set of keywords.
+
+The ppxlib driver also has such an option now to properly configure the lexer before
+attempting to parse source code.
+
+Let's consider the following source file:
+
+  $ cat > test.ml << EOF
+  > let effect = 1
+  > EOF
+
+If passed to the driver as is, it will trigger a parse error:
+
+  $ ./driver.exe --impl test.ml -o ignore.ml
+  File "test.ml", line 1, characters 4-10:
+  1 | let effect = 1
+          ^^^^^^
+  Error: Syntax error
+  [1]
+
+Now, if we use the 5.2 set of keywords, it should happily handle the file:
+
+  $ ./driver.exe --keywords 5.2 --impl test.ml -o ignore.ml
+
+It can also be set using OCAMLPARAM:
+
+  $ OCAMLPARAM=_,keywords=5.2 ./driver.exe --impl test.ml -o ignore.ml
+
+The priority between the CLI option and OCAMLPARAM must be respected, therefore
+both of the following invocation should parse:
+
+  $ OCAMLPARAM=_,keywords=5.2 ./driver.exe --keywords 5.3 --impl test.ml -o ignore.ml
+
+  $ OCAMLPARAM=keywords=5.3,_ ./driver.exe --keywords 5.2 --impl test.ml -o ignore.ml