bug(#631): match fails on empty substs

src/CLI/Runners.hs

@@ -214,7 +214,7 @@ runMatch OptsMatch{..} = do
       condition <- traverse parseConditionThrows _when
       substs <- matchProgramWithRule prog (rule ptn condition) (RuleContext buildTerm)
       if null substs
-        then logDebug "Provided pattern was not matched, no substitutions are built"
+        then throwIO EmptySubstsOnMatch
         else putStrLn (P.printSubsts' substs (_sugarType, UNICODE, _flat, defaultMargin))
   where
     rule :: Expression -> Maybe Y.Condition -> Y.Rule

src/CLI/Types.hs

@@ -37,13 +37,15 @@ data CmdException
   | CouldNotReadFromStdin String
   | CouldNotDataize
   | CouldNotPrintExpressionInXMIR
+  | EmptySubstsOnMatch
   deriving (Exception)
 
 instance Show CmdException where
   show (InvalidCLIArguments msg) = printf "Invalid set of arguments: %s" msg
   show (CouldNotReadFromStdin msg) = printf "Could not read input from stdin\nReason: %s" msg
   show CouldNotDataize = "Could not dataize given program"
   show CouldNotPrintExpressionInXMIR = "Could not print expression with --output=xmir, only program printing is allowed"
+  show EmptySubstsOnMatch = "Provided pattern was not matched, no substitutions are built"
 
 data Command
   = CmdRewrite OptsRewrite

test/CLISpec.hs

@@ -1027,3 +1027,9 @@ spec = do
         testCLIFailed
           ["match", "--pattern=[[!B]]", "--when=hello"]
           ["[ERROR]: Couldn't parse given condition"]
+
+    it "fails on empty substitutions" $
+      withStdin "{Q.x.y}" $
+        testCLIFailed
+          ["match", "--pattern=$.!a"]
+          ["[ERROR]"]