Remove DT_Failed state

At the moment if `-dynamic-too` fails then we rerun the whole pipeline
as if we were just in `-dynamic` mode. I argue this is a misfeature and
we should remove the so-called `DT_Failed` mode.

In what situations do we fall back to `DT_Failed`?

1. If the `dyn_hi` file corresponding to a `hi` file is missing completely.
2. If the interface hash of `dyn_hi` doesn't match the interface hash of `hi`.

What happens in `DT_Failed` mode?

* The whole compiler pipeline is rerun as if the user had just passed `-dynamic`.
* Therefore `dyn_hi/dyn_o` files are used which don't agree with the
  `hi/o` files. (As evidenced by `dynamicToo001` test).
* This is very confusing as now a single compiler invocation has
  produced further `hi`/`dyn_hi` files which are different to each
  other.

Why should we remove it?

* In `--make` mode, which is predominately used `DT_Failed` does not
  work (#19782), there can't be users relying on this functionality.
* In `-c` mode, the recovery doesn't fix the root issue, which is the
  `dyn_hi` and `hi` files are mismatched. We should instead produce an
  error and pass responsibility to the build system using `-c` to ensure
  that the prerequisites for `-dynamic-too` (dyn_hi/hi) files are there
  before we start compiling.
* It is a misfeature to support use cases like `dynamicToo001` which
  allow you to mix different versions of dynamic/non-dynamic interface
  files. It's more likely to lead to subtle bugs in your resulting
  programs where out-dated build products are used rather than a
  deliberate choice.
* In practice, people are usually compiling with `-dynamic-too` rather
  than separately with `-dynamic` and `-static`, so the build products
  always match and `DT_Failed` is only entered due to compiler bugs (see
  !6583)

What should we do instead?

* In `--make` mode, for home packages check during recompilation
  checking that `dyn_hi` and `hi` are both present and agree, recompile
  the modules if they do not.
* For package modules, when loading the interface check that `dyn_hi`
  and `hi` are there and that they agree but fail with an
  error message if they are not.
* In `--oneshot` mode, fail with an error message if the right files
  aren't already there.

Closes #19782 #20446 #9176 #13616

7 files changed, 55 insertions, 0 deletions

diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/A.hs b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/A.hs
new file mode 100644
index 0000000000..f76166afab
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/A.hs
@@ -0,0 +1,6 @@
+
+module A where
+
+a :: Char
+a = 'a'
+
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B1.hs-boot b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B1.hs-boot
new file mode 100644
index 0000000000..4cbf619183
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B1.hs-boot
@@ -0,0 +1,5 @@
+
+module B where
+
+b :: Char
+
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B2.hs-boot b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B2.hs-boot
new file mode 100644
index 0000000000..6f0d8a4aec
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/B2.hs-boot
@@ -0,0 +1,4 @@
+module B where
+
+e :: Char
+
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/C.hs b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/C.hs
new file mode 100644
index 0000000000..40fb0f7695
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/C.hs
@@ -0,0 +1,9 @@
+
+module Main where
+
+import A
+import {-# SOURCE #-} B
+
+main = do print a
+          print b
+
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/Makefile b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/Makefile
new file mode 100644
index 0000000000..94ead80abc
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/Makefile
@@ -0,0 +1,19 @@
+TOP=../../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk
+
+TEST_HC_OPTS_DYN = -dynamic -hisuf dyn_hi -osuf dyn_o
+
+.PHONY: dynamicToo001boot
+# -dynamic-too should notice that the interface files for B.hs-boot don't match,
+#  and issue an error. This is to check the path calculations are correct for boot files.
+dynamicToo001boot:
+	"$(TEST_HC)" $(TEST_HC_OPTS)                     -O -c A.hs
+	"$(TEST_HC)" $(TEST_HC_OPTS) $(TEST_HC_OPTS_DYN) -O -c A.hs
+	cp B1.hs-boot B.hs-boot
+	"$(TEST_HC)" $(TEST_HC_OPTS)                     -O -c B.hs-boot
+	cp B2.hs-boot B.hs-boot
+	"$(TEST_HC)" $(TEST_HC_OPTS) $(TEST_HC_OPTS_DYN) -O -c B.hs-boot
+	# This step fails because the hash of B1 and B2 is different
+	"$(TEST_HC)" $(TEST_HC_OPTS)                     -O -c C.hs -dynamic-too || true
+
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/dynamicToo001boot.stderr b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/dynamicToo001boot.stderr
new file mode 100644
index 0000000000..8b17cac27a
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/dynamicToo001boot.stderr
@@ -0,0 +1,6 @@
+
+C.hs:5:1: error:
+    Dynamic hash doesn't match for ‘B’
+    Normal interface file from ./B.hi-boot
+    Dynamic interface file from ./B.dyn_hi-boot
+    You probably need to recompile ‘B’
diff --git a/testsuite/tests/driver/dynamicToo/dynamicToo001boot/test.T b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/test.T
new file mode 100644
index 0000000000..bca0be654f
--- /dev/null
+++ b/testsuite/tests/driver/dynamicToo/dynamicToo001boot/test.T
@@ -0,0 +1,6 @@
+
+test('dynamicToo001boot',
+     [extra_files(['A.hs', 'B1.hs-boot', 'B2.hs-boot', 'C.hs']),
+      when(opsys('mingw32'), expect_broken(7665)), unless(have_vanilla(), skip),
+      unless(have_dynamic(), skip)],
+     makefile_test, [])