doc\advopt.txt

added --reportConceptFailures switch

compiler/commands.nim

@@ -434,6 +434,8 @@ proc processSwitch(switch, arg: string, pass: TCmdLinePass, info: TLineInfo) =
   of "linedir": processOnOffSwitch({optLineDir}, arg, pass, info)
   of "assertions", "a": processOnOffSwitch({optAssert}, arg, pass, info)
   of "deadcodeelim": processOnOffSwitchG({optDeadCodeElim}, arg, pass, info)
+  of "reportconceptfailures":
+    processOnOffSwitchG({optReportConceptFailures}, arg, pass, info)
   of "threads":
     processOnOffSwitchG({optThreads}, arg, pass, info)
     #if optThreads in gGlobalOptions: incl(gNotes, warnGcUnsafe)

compiler/options.nim

@@ -40,7 +40,7 @@ type                          # please make sure we have under 32 options
   TGlobalOption* = enum       # **keep binary compatible**
     gloptNone, optForceFullMake, optDeadCodeElim,
     optListCmd, optCompileOnly, optNoLinking,
-    optSafeCode,              # only allow safe code
+    optReportConceptFailures, # report 'compiles' or 'concept' matching failures
     optCDebug,                # turn on debugging information
     optGenDynLib,             # generate a dynamic library
     optGenStaticLib,          # generate a static library

compiler/semexprs.nim

@@ -292,8 +292,6 @@ proc semConv(c: PContext, n: PNode): PNode =
 
 proc semCast(c: PContext, n: PNode): PNode =
   ## Semantically analyze a casting ("cast[type](param)")
-  if optSafeCode in gGlobalOptions: localError(n.info, errCastNotInSafeMode)
-  #incl(c.p.owner.flags, sfSideEffect)
   checkSonsLen(n, 2)
   result = newNodeI(nkCast, n.info)
   result.typ = semTypeNode(c, n.sons[0], nil)
@@ -1659,11 +1657,13 @@ proc tryExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   let oldInGenericInst = c.inGenericInst
   let oldProcCon = c.p
   c.generics = @[]
+  var err: string
   try:
     result = semExpr(c, n, flags)
     if msgs.gErrorCounter != oldErrorCount: result = nil
   except ERecoverableError:
-    discard
+    if optReportConceptFailures in gGlobalOptions:
+      err = getCurrentExceptionMsg()
   # undo symbol table changes (as far as it's possible):
   c.compilesContextId = oldCompilesId
   c.generics = oldGenerics
@@ -1677,6 +1677,8 @@ proc tryExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   errorOutputs = oldErrorOutputs
   msgs.gErrorCounter = oldErrorCount
   msgs.gErrorMax = oldErrorMax
+  if optReportConceptFailures in gGlobalOptions and not err.isNil:
+    localError(n.info, err)
 
 proc semCompiles(c: PContext, n: PNode, flags: TExprFlags): PNode =
   # we replace this node by a 'true' or 'false' node:

web/news.txt

@@ -151,6 +151,9 @@ can be found `here <https://nimworkshop.splashthat.com/>`_.
     (issue `#2599 <https://github.com/nim-lang/Nim/issues/2599>`_).
   - The compiler now supports a `bitsize pragma <docs/manual.html#pragmas-bitsize-pragma>`_
     for constructing bitfields.
+  - Added a new ``--reportConceptFailures`` switch for better debugging of
+    concept related type mismatches. This can also be used to debug
+    ``system.compiles`` failures.
 
 
   Language Additions