Rename matrix to range selector in external error messages

The documentation speaks about range vectors and range vector selectors.
This change does not fix all issues, we might still expose the term
"Matrix" in error messages using %T.

promql/parse.go

@@ -609,19 +609,20 @@ func (p *parser) unaryExpr() Expr {
 		case *MatrixSelector:
 			s.Offset = offset
 		default:
-			p.errorf("offset modifier must be preceded by a metric or range selector, but follows a %T instead", e)
+			p.errorf("offset modifier must be preceded by an instant or range selector, but follows a %T instead", e)
 		}
 	}
 
 	return e
 }
 
-// rangeSelector parses a matrix selector based on a given vector selector.
+// rangeSelector parses a matrix (a.k.a. range) selector based on a given
+// vector selector.
 //
 //		<vector_selector> '[' <duration> ']'
 //
 func (p *parser) rangeSelector(vs *VectorSelector) *MatrixSelector {
-	const ctx = "matrix selector"
+	const ctx = "range selector"
 	p.next()
 
 	var erange time.Duration
@@ -948,7 +949,7 @@ func (p *parser) offset() time.Duration {
 	return offset
 }
 
-// vectorSelector parses a new vector selector.
+// vectorSelector parses a new (instant) vector selector.
 //
 //		<metric_identifier> [<label_matchers>]
 //		[<metric_identifier>] <label_matchers>

promql/parse_test.go

@@ -228,6 +228,10 @@ var testExpr = []struct {
 		input:  `*test`,
 		fail:   true,
 		errMsg: "no valid expression found",
+	}, {
+		input:  "1 offset 1d",
+		fail:   true,
+		errMsg: "offset modifier must be preceded by an instant or range selector",
 	},
 	// Vector binary operations.
 	{