Refactor GHCi UI to fix #11606, #12091, #15721, #16096

Instead of parsing and executing a statement or declaration directly we
now parse them first and then execute in a separate step. This gives us
the flexibility to inspect the parsed declaration before execution.
Using this we now inspect parsed declarations, and if it's a single
declaration of form `x = y` we execute it as `let x = y` instead, fixing
a ton of problems caused by poor declaration support in GHCi.

To avoid any users of the modules I left `execStmt` and `runDecls`
unchanged and added `execStmt'` and `runDecls'` which work on parsed
statements/declarations.

9 files changed, 90 insertions, 2 deletions

diff --git a/testsuite/tests/ghci/scripts/T11606.script b/testsuite/tests/ghci/scripts/T11606.script
new file mode 100644
index 0000000000..0fb5fff7ad
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T11606.script
@@ -0,0 +1,5 @@
+:set -Wall
+x = 1 :: Int
+x = 1 :: Int
+x <- return (1 :: Int)
+let x = 1 :: Int
diff --git a/testsuite/tests/ghci/scripts/T11606.stderr b/testsuite/tests/ghci/scripts/T11606.stderr
new file mode 100644
index 0000000000..bbfb7406c6
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T11606.stderr
@@ -0,0 +1,12 @@
+
+<interactive>:3:1: warning: [-Wname-shadowing (in -Wall)]
+    This binding for ‘x’ shadows the existing binding
+      defined at <interactive>:2:1
+
+<interactive>:4:1: warning: [-Wname-shadowing (in -Wall)]
+    This binding for ‘x’ shadows the existing binding
+      defined at <interactive>:3:1
+
+<interactive>:5:5: warning: [-Wname-shadowing (in -Wall)]
+    This binding for ‘x’ shadows the existing binding
+      defined at <interactive>:4:1
diff --git a/testsuite/tests/ghci/scripts/T16089.script b/testsuite/tests/ghci/scripts/T16089.script
new file mode 100644
index 0000000000..d4e6676244
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T16089.script
@@ -0,0 +1,4 @@
+x = [0 .. 100000] :: [Int]
+:sprint x
+x `seq` True
+:sprint x
diff --git a/testsuite/tests/ghci/scripts/T16089.stdout b/testsuite/tests/ghci/scripts/T16089.stdout
new file mode 100644
index 0000000000..7d5cc0b192
--- /dev/null
+++ b/testsuite/tests/ghci/scripts/T16089.stdout
@@ -0,0 +1,3 @@
+x = _
+True
+x = 0 : _
diff --git a/testsuite/tests/ghci/scripts/all.T b/testsuite/tests/ghci/scripts/all.T
index ad4a24f583..2567db4f3d 100755
--- a/testsuite/tests/ghci/scripts/all.T
+++ b/testsuite/tests/ghci/scripts/all.T
@@ -262,7 +262,7 @@ test('T12091', [extra_run_opts('-fobject-code')], ghci_script,
      ['T12091.script'])
 test('T12523', normal, ghci_script, ['T12523.script'])
 test('T12024', normal, ghci_script, ['T12024.script'])
-test('T12158', expect_broken(12158), ghci_script, ['T12158.script'])
+test('T12158', normal, ghci_script, ['T12158.script'])
 test('T12447', normal, ghci_script, ['T12447.script'])
 test('T10249', normal, ghci_script, ['T10249.script'])
 test('T12550', normal, ghci_script, ['T12550.script'])
@@ -293,3 +293,5 @@ test('T15827', normal, ghci_script, ['T15827.script'])
 test('T15898', normal, ghci_script, ['T15898.script'])
 test('T15941', normal, ghci_script, ['T15941.script'])
 test('T16030', normal, ghci_script, ['T16030.script'])
+test('T11606', normal, ghci_script, ['T11606.script'])
+test('T16089', normal, ghci_script, ['T16089.script'])
diff --git a/testsuite/tests/ghci/should_run/T12525.stdout b/testsuite/tests/ghci/should_run/T12525.stdout
index 31049e14d1..652a5cdd03 100644
--- a/testsuite/tests/ghci/should_run/T12525.stdout
+++ b/testsuite/tests/ghci/should_run/T12525.stdout
@@ -1,3 +1,3 @@
-x :: () = _
+x :: () = ()
 y :: () = ()
 class Foo a
diff --git a/testsuite/tests/ghci/should_run/T16096.script b/testsuite/tests/ghci/should_run/T16096.script
new file mode 100644
index 0000000000..8fb9453fd8
--- /dev/null
+++ b/testsuite/tests/ghci/should_run/T16096.script
@@ -0,0 +1,4 @@
+:set -ddump-ds -dsuppress-uniques
+-- These two should desugar to same Core
+let x = [1..] :: [Int]
+x = [1..] :: [Int]
diff --git a/testsuite/tests/ghci/should_run/T16096.stdout b/testsuite/tests/ghci/should_run/T16096.stdout
new file mode 100644
index 0000000000..8b87b7d61c
--- /dev/null
+++ b/testsuite/tests/ghci/should_run/T16096.stdout
@@ -0,0 +1,56 @@
+
+==================== Desugared ====================
+letrec {
+  x :: [GHC.Types.Int]
+  [LclId]
+  x = let {
+        $dEnum :: GHC.Enum.Enum GHC.Types.Int
+        [LclId]
+        $dEnum = GHC.Enum.$fEnumInt } in
+      letrec {
+        x :: [GHC.Types.Int]
+        [LclId]
+        x = GHC.Enum.enumFrom
+              @ GHC.Types.Int $dEnum (GHC.Types.I# 1#); } in
+      x; } in
+GHC.Base.returnIO
+  @ [()]
+  (GHC.Types.:
+     @ ()
+     (GHC.Prim.unsafeCoerce#
+        @ 'GHC.Types.LiftedRep
+        @ 'GHC.Types.LiftedRep
+        @ [GHC.Types.Int]
+        @ ()
+        x)
+     (GHC.Types.[] @ ()))
+
+
+
+==================== Desugared ====================
+letrec {
+  x :: [GHC.Types.Int]
+  [LclId]
+  x = let {
+        $dEnum :: GHC.Enum.Enum GHC.Types.Int
+        [LclId]
+        $dEnum = GHC.Enum.$fEnumInt } in
+      letrec {
+        x :: [GHC.Types.Int]
+        [LclId]
+        x = GHC.Enum.enumFrom
+              @ GHC.Types.Int $dEnum (GHC.Types.I# 1#); } in
+      x; } in
+GHC.Base.returnIO
+  @ [()]
+  (GHC.Types.:
+     @ ()
+     (GHC.Prim.unsafeCoerce#
+        @ 'GHC.Types.LiftedRep
+        @ 'GHC.Types.LiftedRep
+        @ [GHC.Types.Int]
+        @ ()
+        x)
+     (GHC.Types.[] @ ()))
+
+
diff --git a/testsuite/tests/ghci/should_run/all.T b/testsuite/tests/ghci/should_run/all.T
index ea734e74aa..004794b5e5 100644
--- a/testsuite/tests/ghci/should_run/all.T
+++ b/testsuite/tests/ghci/should_run/all.T
@@ -56,3 +56,5 @@ test('T15633b',
       extra_hc_opts("-package-db tc-plugin-ghci/pkg.plugins01/local.package.conf")
       ],
      ghci_script, ['T15633b.script'])
+
+test('T16096', just_ghci, ghci_script, ['T16096.script'])