fix for issue #895: source not found for Panic traces

src/EVM/Dapp.hs

@@ -160,9 +160,35 @@ showTraceLocation dapp trace =
     Nothing -> Left "<no source map>"
     Just sm ->
       case srcMapCodePos dapp.sources sm of
-        Nothing -> Left "<source not found>"
         Just (fileName, lineIx) ->
           Right (pack fileName <> ":" <> pack (show lineIx))
+        -- srcmap points to a file not in the source cache (e.g. compiler-
+        -- generated panic handler).  Walk backwards through the contract's
+        -- srcmap to find the nearest entry with a valid source location —
+        -- this typically resolves to the assert/require that triggered the
+        -- error.
+        Nothing ->
+          case fallbackSrcPos dapp trace of
+            Just (fileName, lineIx) ->
+              Right (pack fileName <> ":" <> pack (show lineIx))
+            Nothing -> Left "<source not found>"
+
+-- | Walk backwards from the current opIx to find the nearest srcmap entry
+-- whose file index exists in the source cache.
+fallbackSrcPos :: DappInfo -> Trace -> Maybe (FilePath, Int)
+fallbackSrcPos dapp trace = do
+  sol <- findSrc trace.contract dapp
+  let srcmaps = case trace.contract.code of
+        InitCode _ _ -> sol.creationSrcmap
+        RuntimeCode _ -> sol.runtimeSrcmap
+        UnknownCode _ -> mempty
+  go (trace.opIx - 1) srcmaps
+  where
+    go i srcmaps
+      | i < 0     = Nothing
+      | otherwise = case Seq.lookup i srcmaps >>= srcMapCodePos dapp.sources of
+          Just pos -> Just pos
+          Nothing  -> go (i - 1) srcmaps
 
 srcMapCodePos :: SourceCache -> SrcMap -> Maybe (FilePath, Int)
 srcMapCodePos cache sm =

test/EVM/Test/FoundryTests.hs

@@ -118,6 +118,10 @@ tests = testGroup "Foundry tests"
     , test "Keccak" $ do
         let testFile = "test/contracts/pass/keccak.sol"
         executeSingleMethod testFile "prove_access" >>= assertEqualM "test result" (True, True)
+    , test "Panic-Source-Location" $ do
+        -- Regression test for #895: panic in a called contract should not show "<source not found>"
+        let testFile = "test/contracts/fail/assertPanic.sol"
+        executeSingleMethod testFile "prove_panic" >>= assertEqualM "prove_panic" (False, False)
     ]
 
 executeSingleMethod :: (App m, MonadMask m) => FilePath -> Text -> m (Bool, Bool)

test/contracts/fail/assertPanic.sol

@@ -0,0 +1,15 @@
+import "forge-std/Test.sol";
+
+contract PanicTest is Test {
+    function prove_panic() public {
+        Panicker p = new Panicker();
+        p.doPanic();
+        assert(true);
+    }
+}
+
+contract Panicker {
+    function doPanic() public pure {
+        assert(false);
+    }
+}