66 lines
2.1 KiB
Perl
66 lines
2.1 KiB
Perl
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The --use-compiler-pp flag can be used when using the driver's source code
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output, either directly when generating a .corrected file or to force
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printing the AST as source using the installed compiler's printer.
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Our driver has a deriver and an extension that produces a pattern-matching with
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named existentials.
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This feature has been introduced in 4.13 so the syntax is unsupported before that.
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If we run the driver in source output mode, without the `--use-compiler-pp` flag,
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it will successfully print out the source using the 4.13 syntax. If we're running
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on an older compiler, like we are for this test, that can be troublesome.
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If instead we use the flag, this will force the migration thus causing an error as
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named existentials can't be migrated down to 4.12.
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Let's consider the following file:
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$ cat > test.ml << EOF
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> [%%named_existentials]
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> EOF
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Running the driver will generate a function with a single pattern matching in it:
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$ ./driver.exe test.ml
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let f x = match x with | Constructor (type a) _ -> ()
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Now if we run it with `--use-compiler-pp`, we should get the migration error:
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$ ./driver.exe --use-compiler-pp test.ml
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File "test.ml", line 1, characters 0-22:
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1 | [%%named_existentials]
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^^^^^^^^^^^^^^^^^^^^^^
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Error: migration error: existentials in pattern-matching is not supported before OCaml 4.13
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[1]
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This should also work for correction based code gen:
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$ cat > test_inline.ml << EOF
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> type t = int
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> [@@deriving_inline named_existentials]
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> [@@@end]
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> EOF
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If we run the driver without `--use-compiler-pp`:
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$ ./driver.exe test_inline.ml -diff-cmd -
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type t = int[@@deriving_inline named_existentials]
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[@@@end ]
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$ cat test_inline.ml.ppx-corrected
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type t = int
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[@@deriving_inline named_existentials]
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let _ = fun (_ : t) -> ()
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let f x = match x with | Constructor (type a) _ -> ()
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let _ = f
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[@@@end]
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and with the flag:
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$ ./driver.exe test_inline.ml -diff-cmd - --use-compiler-pp
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File "test_inline.ml", lines 1-2, characters 0-38:
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1 | type t = int
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2 | [@@deriving_inline named_existentials]
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Error: migration error: existentials in pattern-matching is not supported before OCaml 4.13
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[1]
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