Include go-cty stdlib functions in HCL file scope

Signed-off-by: Patrick Van Stee <patrick@vanstee.me>

bake/hcl.go

@@ -7,6 +7,61 @@ import (
 	hcl "github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/hclsimple"
 	"github.com/zclconf/go-cty/cty"
+	"github.com/zclconf/go-cty/cty/function"
+	"github.com/zclconf/go-cty/cty/function/stdlib"
+)
+
+// Collection of functions expected to be generally useful in cty-using
+// applications, which HCL supports. This set of functions will be available to
+// be called in HCL files.
+var (
+	functions = map[string]function.Function{
+		"absolute":               stdlib.AbsoluteFunc,
+		"add":                    stdlib.AddFunc,
+		"and":                    stdlib.AndFunc,
+		"byteslen":               stdlib.BytesLenFunc,
+		"bytesslice":             stdlib.BytesSliceFunc,
+		"csvdecode":              stdlib.CSVDecodeFunc,
+		"coalesce":               stdlib.CoalesceFunc,
+		"concat":                 stdlib.ConcatFunc,
+		"divide":                 stdlib.DivideFunc,
+		"equal":                  stdlib.EqualFunc,
+		"formatdate":             stdlib.FormatDateFunc,
+		"format":                 stdlib.FormatFunc,
+		"formatlist":             stdlib.FormatListFunc,
+		"greaterthan":            stdlib.GreaterThanFunc,
+		"greaterthanorequalto":   stdlib.GreaterThanOrEqualToFunc,
+		"hasindex":               stdlib.HasIndexFunc,
+		"index":                  stdlib.IndexFunc,
+		"int":                    stdlib.IntFunc,
+		"jsondecode":             stdlib.JSONDecodeFunc,
+		"jsonencode":             stdlib.JSONEncodeFunc,
+		"length":                 stdlib.LengthFunc,
+		"lessthan":               stdlib.LessThanFunc,
+		"lessthanorequalto":      stdlib.LessThanOrEqualToFunc,
+		"lower":                  stdlib.LowerFunc,
+		"max":                    stdlib.MaxFunc,
+		"min":                    stdlib.MinFunc,
+		"modulo":                 stdlib.ModuloFunc,
+		"multiply":               stdlib.MultiplyFunc,
+		"negate":                 stdlib.NegateFunc,
+		"notequal":               stdlib.NotEqualFunc,
+		"not":                    stdlib.NotFunc,
+		"or":                     stdlib.OrFunc,
+		"range":                  stdlib.RangeFunc,
+		"regexall":               stdlib.RegexAllFunc,
+		"regex":                  stdlib.RegexFunc,
+		"reverse":                stdlib.ReverseFunc,
+		"sethaselement":          stdlib.SetHasElementFunc,
+		"setintersection":        stdlib.SetIntersectionFunc,
+		"setsubtract":            stdlib.SetSubtractFunc,
+		"setsymmetricdifference": stdlib.SetSymmetricDifferenceFunc,
+		"setunion":               stdlib.SetUnionFunc,
+		"strlen":                 stdlib.StrlenFunc,
+		"substr":                 stdlib.SubstrFunc,
+		"subtract":               stdlib.SubtractFunc,
+		"upper":                  stdlib.UpperFunc,
+	}
 )
 
 func ParseHCL(dt []byte, fn string) (*Config, error) {
@@ -18,6 +73,7 @@ func ParseHCL(dt []byte, fn string) (*Config, error) {
 
 	ctx := &hcl.EvalContext{
 		Variables: variables,
+		Functions: functions,
 	}
 
 	var c Config