[ fix #1970 ] error on mod self ref (#1977)

src/Idris/ModTree.idr

@@ -85,11 +85,14 @@ mkModTree loc done modFP mod
                            do file <- maybe (nsToSource loc mod) pure modFP
                               modInfo <- readHeader file mod
                               let imps = map path (imports modInfo)
-                              ms <- traverse (mkModTree loc (mod :: done) Nothing) imps
-                              let mt = MkModTree mod (Just file) ms
-                              all <- get AllMods
-                              put AllMods ((mod, mt) :: all)
-                              pure mt
+                              if mod `elem` imps
+                                then coreFail $ CyclicImports [mod, mod]
+                                else do
+                                  ms <- traverse (mkModTree loc (mod :: done) Nothing) imps
+                                  let mt = MkModTree mod (Just file) ms
+                                  all <- get AllMods
+                                  put AllMods ((mod, mt) :: all)
+                                  pure mt
                          Just m => pure m)
                 -- Couldn't find source, assume it's in a package directory
                 (\err =>

tests/Main.idr

@@ -194,7 +194,7 @@ idrisTests = MkTestPool "Misc" [] Nothing
        -- Eta equality
        "eta001",
        -- Modules and imports
-       "import001", "import002", "import003", "import004", "import005",
+       "import001", "import002", "import003", "import004", "import005", "import006",
        -- Implicit laziness, lazy evaluation
        "lazy001", "lazy002",
        -- Namespace blocks

tests/idris2/import006/A/B.idr

@@ -0,0 +1,3 @@
+module A.B
+
+import A.B

tests/idris2/import006/A/C.idr

@@ -0,0 +1,3 @@
+module A.C
+
+import A.B

tests/idris2/import006/cyclic.ipkg

@@ -0,0 +1,3 @@
+package cyclic
+
+modules = A.B, A.C

tests/idris2/import006/expected

@@ -0,0 +1 @@
+Uncaught error: Module imports form a cycle: A.B -> A.B

tests/idris2/import006/run

@@ -0,0 +1,3 @@
+rm -rf build
+
+$1 --no-color --console-width 0 --no-banner --build cyclic.ipkg