util, lang, etcd: Move the error type to our util package

We use this error in a lot of places, let's centralize it a bit.

lang/ast/structs.go

@@ -160,16 +160,16 @@ const (
 	scopedOrderingPrefix = "scoped:"
 
 	// ErrNoStoredScope is an error that tells us we can't get a scope here.
-	ErrNoStoredScope = interfaces.Error("scope is not stored in this node")
+	ErrNoStoredScope = util.Error("scope is not stored in this node")
 
 	// ErrFuncPointerNil is an error that explains the function pointer for
 	// table lookup is missing. If this happens, it's most likely a
 	// programming error.
-	ErrFuncPointerNil = interfaces.Error("missing func pointer for table")
+	ErrFuncPointerNil = util.Error("missing func pointer for table")
 
 	// ErrTableNoValue is an error that explains the table is missing a
 	// value. If this happens, it's most likely a programming error.
-	ErrTableNoValue = interfaces.Error("missing value in table")
+	ErrTableNoValue = util.Error("missing value in table")
 )
 
 var (

lang/interfaces/error.go

@@ -29,19 +29,17 @@
 
 package interfaces
 
-// Error is a constant error type that implements error.
-type Error string
-
-// Error fulfills the error interface of this type.
-func (e Error) Error() string { return string(e) }
+import (
+	"github.com/purpleidea/mgmt/util"
+)
 
 const (
 	// ErrTypeCurrentlyUnknown is returned from the Type() call on Expr if
 	// unification didn't run successfully and the type isn't obvious yet.
-	ErrTypeCurrentlyUnknown = Error("type is currently unknown")
+	ErrTypeCurrentlyUnknown = util.Error("type is currently unknown")
 
 	// ErrExpectedFileMissing is returned when a file that is used by an
 	// import is missing. This might signal the downloader, or it might
 	// signal a permanent error.
-	ErrExpectedFileMissing = Error("file is currently missing")
+	ErrExpectedFileMissing = util.Error("file is currently missing")
 )

lang/parser/lexparse.go

@@ -46,21 +46,21 @@ import (
 
 // These constants represent the different possible lexer/parser errors.
 const (
-	ErrLexerUnrecognized      = interfaces.Error("unrecognized")
-	ErrLexerUnrecognizedCR    = interfaces.Error("unrecognized carriage return")
-	ErrLexerStringBadEscaping = interfaces.Error("string: bad escaping")
-	ErrLexerIntegerOverflow   = interfaces.Error("integer: overflow")
-	ErrLexerFloatOverflow     = interfaces.Error("float: overflow")
-	ErrParseError             = interfaces.Error("parser")
-	ErrParseSetType           = interfaces.Error("can't set return type in parser")
-	ErrParseResFieldInvalid   = interfaces.Error("can't use unknown resource field")
-	ErrParseAdditionalEquals  = interfaces.Error(errstrParseAdditionalEquals)
-	ErrParseExpectingComma    = interfaces.Error(errstrParseExpectingComma)
+	ErrLexerUnrecognized      = util.Error("unrecognized")
+	ErrLexerUnrecognizedCR    = util.Error("unrecognized carriage return")
+	ErrLexerStringBadEscaping = util.Error("string: bad escaping")
+	ErrLexerIntegerOverflow   = util.Error("integer: overflow")
+	ErrLexerFloatOverflow     = util.Error("float: overflow")
+	ErrParseError             = util.Error("parser")
+	ErrParseSetType           = util.Error("can't set return type in parser")
+	ErrParseResFieldInvalid   = util.Error("can't use unknown resource field")
+	ErrParseAdditionalEquals  = util.Error(errstrParseAdditionalEquals)
+	ErrParseExpectingComma    = util.Error(errstrParseExpectingComma)
 )
 
 // LexParseErr is a permanent failure error to notify about borkage.
 type LexParseErr struct {
-	Err interfaces.Error
+	Err util.Error
 	Str string
 	Row int // this is zero-indexed (the first line is 0)
 	Col int // this is zero-indexed (the first char is 0)

lang/unification/interfaces.go

@@ -35,12 +35,13 @@ import (
 
 	"github.com/purpleidea/mgmt/lang/interfaces"
 	"github.com/purpleidea/mgmt/lang/types"
+	"github.com/purpleidea/mgmt/util"
 )
 
 const (
 	// ErrAmbiguous means we couldn't find a solution, but we weren't
 	// inconsistent.
-	ErrAmbiguous = interfaces.Error("can't unify, no equalities were consumed, we're ambiguous")
+	ErrAmbiguous = util.Error("can't unify, no equalities were consumed, we're ambiguous")
 
 	// StrategyNameKey is the string key used when choosing a solver name.
 	StrategyNameKey = "name"