Merge #268

268: Improve internal reporting of errors in `vm`/`vmgen` r=saem a=zerbina

Reporting of guest code related errors was done in an inconsistent
manner via either `stackTrace` or `globalReport`, where `stackTrace` used
`localReport` and an injected `return` statement to terminate the
execution loop. `stackTrace` was sometimes used in nested functions,
thus not terminating execution at all.

### Changes
Both the execution engine and `vmgen` now use exceptions for error
propagation internally, translating them into a result value at their
respective interface edges. In case of an error, the result value stores the
error report. Otherwise, it stores the actual result.

In addition, some usages of `globalReport` are also replaced with the
 new error propagation mechanism.

Depending on whether or not a VM invocation is expected to return
something, errors reported from VM execution and/or `vmgen` are either
turned into a `nkError` node or handled directly via `handleReport`

Fixes #160



Co-authored-by: zerbina <100542850+zerbina@users.noreply.github.com>

compiler/ast/reports.nim

@@ -923,7 +923,7 @@ type
 func incl*(s: var ReportSet, id: ReportId) = s.ids.incl uint32(id)
 func contains*(s: var ReportSet, id: ReportId): bool = s.ids.contains uint32(id)
 
-func addReport*(list: var ReportList, report: Report): ReportId =
+func addReport*(list: var ReportList, report: sink Report): ReportId =
   ## Add report to the report list
   list.list.add report
   result = ReportId(uint32(list.list.high) + 1)

compiler/sem/sem.nim

@@ -449,15 +449,11 @@ proc tryConstExpr(c: PContext, n: PNode): PNode =
   c.config.m.errorOutputs = {}
   c.config.errorMax = high(int) # `setErrorMaxHighMaybe` not appropriate here
 
-  try:
-    result = evalConstExpr(c.module, c.idgen, c.graph, e)
-    if result == nil or result.kind == nkEmpty:
-      result = nil
-    else:
-      result = fixupTypeAfterEval(c, result, e)
-
-  except ERecoverableError:
+  result = evalConstExpr(c.module, c.idgen, c.graph, e)
+  if result == nil or result.kind in {nkEmpty, nkError}:
     result = nil
+  else:
+    result = fixupTypeAfterEval(c, result, e)
 
   c.config.errorCounter = oldErrorCount
   c.config.errorMax = oldErrorMax
@@ -475,13 +471,20 @@ proc semConstExpr(c: PContext, n: PNode): PNode =
   if result == nil:
     #if e.kind == nkEmpty: globalReport(n.info, errConstExprExpected)
     result = evalConstExpr(c.module, c.idgen, c.graph, e)
-    if result == nil or result.kind == nkEmpty:
-      if e.info != n.info:
+    assert result != nil
+    case result.kind
+    of {nkEmpty, nkError}:
+      let withContext = e.info != n.info
+      if withContext:
         pushInfoContext(c.config, n.info)
+
+      if result.kind == nkEmpty:
         localReport(c.config, e.info, SemReport(kind: rsemConstExprExpected))
-        popInfoContext(c.config)
       else:
-        localReport(c.config, e.info, SemReport(kind: rsemConstExprExpected))
+        localReport(c.config, result)
+
+      if withContext:
+        popInfoContext(c.config)
       # error correction:
       result = e
     else: