fix: allow multiple calls to subst with a regexp

This change disables the ``checkRegex`` helper when a regexp is used by
the builtin ``subst`` as there will be no symbols created on the symbol
table, and the compiler already compiles and appends the regexp to the
regexp table for use by the VM.

fixes: #693, #810

Author: terencehonles

internal/runtime/compiler/checker/checker.go

@@ -35,6 +35,7 @@ type checker struct {
 	tooDeep           bool
 	maxRecursionDepth int
 	maxRegexLength    int
+	skipRegexCheck    bool
 }
 
 // Check performs a semantic check of the astNode, and returns a potentially
@@ -83,6 +84,12 @@ func (c *checker) VisitBefore(node ast.Node) (ast.Visitor, ast.Node) {
 		glog.V(2).Infof("Created new scope %v in condstmt", n.Scope)
 		return c, n
 
+	case *ast.BuiltinExpr:
+		if n.Name == "subst" {
+			c.skipRegexCheck = true
+		}
+		return c, n
+
 	case *ast.CaprefTerm:
 		if n.Symbol == nil {
 			sym := c.scope.Lookup(n.Name, symbol.CaprefSymbol)
@@ -821,6 +828,10 @@ func (c *checker) VisitAfter(node ast.Node) ast.Node {
 				return n
 			}
 
+		case "subst":
+			c.skipRegexCheck = false
+			return n
+
 		case "tolower":
 			if !types.Equals(gotType.Args[0], types.String) {
 				c.errors.Add(n.Args.(*ast.ExprList).Children[0].Pos(), fmt.Sprintf("Expecting a String for argument 1 of tolower(), not %v.", gotType.Args[0]))
@@ -838,7 +849,9 @@ func (c *checker) VisitAfter(node ast.Node) ast.Node {
 			return n
 		}
 		n.Pattern = pe.pattern.String()
-		c.checkRegex(n.Pattern, n)
+		if !c.skipRegexCheck {
+			c.checkRegex(n.Pattern, n)
+		}
 		return n
 
 	case *ast.PatternFragment:

internal/runtime/compiler/checker/checker_test.go

@@ -576,6 +576,11 @@ foo = subst(",", "", $1)
 }`},
 	{"regexp subst", `
 subst(/\d+/, "d", "1234")
+`},
+	{"regexp subst twice", `
+text value
+value = subst(/[a-zA-Z]+/, "a", "1234abcd")
+value = subst(/\d+/, "d", value)
 `},
 }