progress

* various fixes
* the beginnings of a type-based alias analysis
* ...

compiler/ast/report_enums.nim

@@ -627,6 +627,8 @@ type
     rsemCannotBorrowImmutable
     rsemCannotBorrow2
     rsemMustBeConstructor
+    rsemOverlappingParamBorrows
+    rsemPotentialAliasViolation
 
     rsemCyclicTree
     rsemCyclicDependency

compiler/ast/reports_sem.nim

@@ -202,7 +202,7 @@ type
       of rsemDiagnostics:
         diag*: SemDiagnostics
 
-      of rsemIllegalBorrow:
+      of rsemIllegalBorrow, rsemOverlappingParamBorrows:
         borrow*: PNode
         isProblemMutation*: bool
         problem*, usage*: TLineInfo

compiler/front/cli_reporter.nim

@@ -576,6 +576,15 @@ proc reportBody*(conf: ConfigRef, r: SemReport): string =
       result.add "cannot borrow from expression: " & $r.ast
     of rsemMustBeConstructor:
       result.add "RHS of compound view assignment must be constructor expression"
+    of rsemOverlappingParamBorrows:
+      if r.isProblemMutation:
+        result.add "cannot create another mutable borrow\n"
+        result.add "$1 another, potentially overlapping, mutable borrow was created here" % [conf.toStr(r.usage)]
+      else:
+        result.add "cannot create mutable borrow\n"
+        result.add "$1 a potentially overlapping immutable borrow was created here" % [conf.toStr(r.usage)]
+    of rsemPotentialAliasViolation:
+      result.add "cannot create borrow because the location could be modified through '$1'" % [$r.ast]
 
     of rsemPragmaRecursiveDependency:
       result.add "recursive dependency: "