unikernel/duniverse/dune_/test/blackbox-tests/test-cases/pp-cwd.t/run.t

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+We test two different aspects of preprocessors:
+
+* The directory in which they run
+* How they reference their file dependencies (relative to what?)
+
+  $ cat >dune-project <<EOF
+  > (lang dune 2.9)
+  > EOF
+
+First, we demonstrate that preprocessors run from the context root:
+
+  $ DIR=1
+  $ mkdir $DIR
+  $ cat >$DIR/dune <<EOF
+  > (test
+  >  (name test)
+  >  (preprocess
+  >   (action (run %{bin:dunepp} %{input-file} $DIR))))
+  > EOF
+  $ cat >$DIR/test.ml <<EOF
+  > print_endline _STRING_
+  > EOF
+  $ dune runtest $DIR
+  running preprocessor in $TESTCASE_ROOT/_build/default
+  Hello, world!
+
+While running it from the context root is good for error messages, it makes
+referencing processor dependencies quite awkward:
+
+  $ DIR=2
+  $ mkdir $DIR
+  $ touch $DIR/dep
+  $ cat >$DIR/dune <<EOF
+  > (test
+  >  (name test)
+  >  (preprocessor_deps dep)
+  >  (preprocess
+  >   (action (run %{bin:dunepp} %{input-file} $DIR dep))))
+  > EOF
+  $ cat >$DIR/test.ml <<EOF
+  > print_endline _STRING_
+  > EOF
+  $ dune runtest $DIR
+  running preprocessor in $TESTCASE_ROOT/_build/default
+  dep dep exists = false
+  dep 2/dep exists = true
+  Hello, world!