From 07e8590f254ca586d3e0ac37e1fe33a3721716ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Per=20=C3=96stlund?= <perost86@gmail.com>
Date: Mon, 10 Aug 2020 13:13:38 +0200
Subject: [PATCH] [NF] Detect recursive bindings during evaluation.

---
 OMCompiler/Compiler/NFFrontEnd/NFBinding.mo   |  5 +++++
 OMCompiler/Compiler/NFFrontEnd/NFCeval.mo     | 14 +++++++++++++
 .../flattening/modelica/scodeinst/Makefile    |  1 +
 .../modelica/scodeinst/RecursiveConstants1.mo | 20 +++++++++++++++++++
 4 files changed, 40 insertions(+)
 create mode 100644 testsuite/flattening/modelica/scodeinst/RecursiveConstants1.mo

diff --git a/OMCompiler/Compiler/NFFrontEnd/NFBinding.mo b/OMCompiler/Compiler/NFFrontEnd/NFBinding.mo
index b2bb6da194f..240c9a955cf 100644
--- a/OMCompiler/Compiler/NFFrontEnd/NFBinding.mo
+++ b/OMCompiler/Compiler/NFFrontEnd/NFBinding.mo
@@ -105,6 +105,11 @@ public
     list<ErrorTypes.TotalMessage> errors;
   end INVALID_BINDING;
 
+  record EVALUATING_BINDING
+    "Used by the constant evaluation to detect recursive bindings."
+    Binding binding;
+  end EVALUATING_BINDING;
+
 public
   function fromAbsyn
     input Option<Absyn.Exp> bindingExp;
diff --git a/OMCompiler/Compiler/NFFrontEnd/NFCeval.mo b/OMCompiler/Compiler/NFFrontEnd/NFCeval.mo
index b66c8fd2fb1..e1485879409 100644
--- a/OMCompiler/Compiler/NFFrontEnd/NFCeval.mo
+++ b/OMCompiler/Compiler/NFFrontEnd/NFCeval.mo
@@ -65,6 +65,7 @@ import TypeCheck = NFTypeCheck;
 import ExpandExp = NFExpandExp;
 import ElementSource;
 import Flags;
+import Prefixes = NFPrefixes;
 
 public
 uniontype EvalTarget
@@ -399,6 +400,11 @@ algorithm
         if binding.evaluated then
           exp := binding.bindingExp;
         else
+          // Mark the binding as currently being evaluated, to detect loops due
+          // to mutually dependent constants/parameters.
+          comp := Component.setBinding(Binding.EVALUATING_BINDING(binding), comp);
+          InstNode.updateComponent(comp, node);
+
           exp := evalExp_impl(binding.bindingExp, target);
 
           binding.bindingExp := exp;
@@ -417,6 +423,14 @@ algorithm
       then
         (defaultExp, false);
 
+    case Binding.EVALUATING_BINDING()
+      algorithm
+        Error.addSourceMessage(Error.CIRCULAR_PARAM,
+          {InstNode.name(node), Prefixes.variabilityString(Component.variability(comp))},
+          InstNode.info(node));
+      then
+        fail();
+
     else
       algorithm
         Error.addInternalError(getInstanceName() + " failed on untyped binding", sourceInfo());
diff --git a/testsuite/flattening/modelica/scodeinst/Makefile b/testsuite/flattening/modelica/scodeinst/Makefile
index 9d6a1ca4d1e..3066957f91c 100644
--- a/testsuite/flattening/modelica/scodeinst/Makefile
+++ b/testsuite/flattening/modelica/scodeinst/Makefile
@@ -734,6 +734,7 @@ RecordConstructor2.mo \
 RecordExtends1.mo \
 RecordExtends2.mo \
 RecordUnknownDim1.mo \
+RecursiveConstants1.mo \
 RecursiveExtends1.mo \
 RecursiveExtends3.mo \
 RecursiveInst1.mo \
diff --git a/testsuite/flattening/modelica/scodeinst/RecursiveConstants1.mo b/testsuite/flattening/modelica/scodeinst/RecursiveConstants1.mo
new file mode 100644
index 00000000000..5186fa770ae
--- /dev/null
+++ b/testsuite/flattening/modelica/scodeinst/RecursiveConstants1.mo
@@ -0,0 +1,20 @@
+// name: RecursiveConstants1
+// keywords:
+// status: incorrect
+// cflags: -d=newInst
+//
+
+model RecursiveConstants1
+  constant Real x = y;
+  constant Real y = x;
+end RecursiveConstants1;
+
+// Result:
+// Error processing file: RecursiveConstants1.mo
+// [flattening/modelica/scodeinst/RecursiveConstants1.mo:9:3-9:22:writable] Error: Variable 'y' has a cyclic dependency and has variability constant.
+//
+// # Error encountered! Exiting...
+// # Please check the error message and the flags.
+//
+// Execution failed!
+// endResult