perf: various small improvements (#7357)

Mostly by having more built-in functions check that they
actually *did* something, or can return an operand instead
of allocating a result.

This saves about 200k allocations in `regal lint bundle`.

Signed-off-by: Anders Eknert <anders@styra.com>

v1/ast/interning.go

@@ -63,6 +63,29 @@ func HasInternedIntNumberTerm(i int) bool {
 	return i >= -1 && i < len(intNumberTerms)
 }
 
+func InternedStringTerm(s string) *Term {
+	if term, ok := internedStringTerms[s]; ok {
+		return term
+	}
+
+	return StringTerm(s)
+}
+
+var internedStringTerms = map[string]*Term{
+	"":   InternedEmptyString,
+	"0":  StringTerm("0"),
+	"1":  StringTerm("1"),
+	"2":  StringTerm("2"),
+	"3":  StringTerm("3"),
+	"4":  StringTerm("4"),
+	"5":  StringTerm("5"),
+	"6":  StringTerm("6"),
+	"7":  StringTerm("7"),
+	"8":  StringTerm("8"),
+	"9":  StringTerm("9"),
+	"10": StringTerm("10"),
+}
+
 var stringToIntNumberTermMap = map[string]*Term{
 	"-1":  minusOneTerm,
 	"0":   intNumberTerms[0],

v1/ast/parser.go

@@ -1641,6 +1641,10 @@ func (p *Parser) parseNumber() *Term {
 
 func (p *Parser) parseString() *Term {
 	if p.s.lit[0] == '"' {
+		if p.s.lit == "\"\"" {
+			return NewTerm(InternedEmptyString.Value).SetLocation(p.s.Loc())
+		}
+
 		var s string
 		err := json.Unmarshal([]byte(p.s.lit), &s)
 		if err != nil {

v1/topdown/object.go

@@ -21,6 +21,16 @@ func builtinObjectUnion(_ BuiltinContext, operands []*ast.Term, iter func(*ast.T
 		return err
 	}
 
+	if objA.Len() == 0 {
+		return iter(operands[1])
+	}
+	if objB.Len() == 0 {
+		return iter(operands[0])
+	}
+	if objA.Compare(objB) == 0 {
+		return iter(operands[0])
+	}
+
 	r := mergeWithOverwrite(objA, objB)
 
 	return iter(ast.NewTerm(r))

v1/topdown/regex.go

@@ -260,6 +260,9 @@ func builtinRegexReplace(bctx BuiltinContext, operands []*ast.Term, iter func(*a
 	}
 
 	res := re.ReplaceAllString(string(base), string(value))
+	if res == string(base) {
+		return iter(operands[0])
+	}
 
 	return iter(ast.StringTerm(res))
 }

v1/topdown/strings.go

@@ -324,6 +324,10 @@ func builtinSubstring(_ BuiltinContext, operands []*ast.Term, iter func(*ast.Ter
 			return iter(ast.StringTerm(sbase[startIndex:]))
 		}
 
+		if startIndex == 0 && length >= len(sbase) {
+			return iter(operands[0])
+		}
+
 		upto := startIndex + length
 		if len(sbase) < upto {
 			upto = len(sbase)
@@ -331,6 +335,10 @@ func builtinSubstring(_ BuiltinContext, operands []*ast.Term, iter func(*ast.Ter
 		return iter(ast.StringTerm(sbase[startIndex:upto]))
 	}
 
+	if startIndex == 0 && length >= utf8.RuneCountInString(sbase) {
+		return iter(operands[0])
+	}
+
 	runes := []rune(base)
 
 	if startIndex >= len(runes) {
@@ -641,7 +649,7 @@ func builtinSprintf(_ BuiltinContext, operands []*ast.Term, iter func(*ast.Term)
 	if s == "%d" && astArr.Len() == 1 {
 		if n, ok := astArr.Elem(0).Value.(ast.Number); ok {
 			if i, ok := n.Int(); ok {
-				return iter(ast.StringTerm(strconv.Itoa(i)))
+				return iter(ast.InternedStringTerm(strconv.Itoa(i)))
 			}
 		}
 	}