From 8cb4a48e2e528054685080ffcc4ed424a026e153 Mon Sep 17 00:00:00 2001
From: Tobias Guggenmos <tguggenm@redhat.com>
Date: Mon, 16 Dec 2019 14:58:47 +0100
Subject: [PATCH] PromQL: Parse label sets using the generated parser (#6432)

* Add grammar for label_sets
* Parse label Sets using the generated parser
* Allow trailing commas for label sets and selectors
* Add test to trigger all possible error messages for label matchers

Signed-off-by: Tobias Guggenmos <tguggenm@redhat.com>
---
 promql/generated_parser.y    |  80 +++++++++---
 promql/generated_parser.y.go | 229 +++++++++++++++++++++++++----------
 promql/parse.go              |  89 +-------------
 promql/parse_test.go         |  35 +++++-
 4 files changed, 262 insertions(+), 171 deletions(-)

diff --git a/promql/generated_parser.y b/promql/generated_parser.y
index f8aa530686..6eecbdbb9a 100644
--- a/promql/generated_parser.y
+++ b/promql/generated_parser.y
@@ -20,10 +20,13 @@
 %}
 
 %union {
-    node Node
-    item Item
-    matchers []*labels.Matcher
-    matcher  *labels.Matcher
+    node      Node
+    item      Item
+    matchers  []*labels.Matcher
+    matcher   *labels.Matcher
+    labelSet  []labels.Label
+    label     labels.Label
+    labels    labels.Labels
 }
 
 
@@ -102,6 +105,7 @@
 %token	startSymbolsStart
 // Start symbols for the generated parser.
 %token START_LABELS
+%token START_LABEL_SET
 %token	startSymbolsEnd
 
 %type <matchers> label_matchers label_match_list
@@ -109,30 +113,40 @@
 
 %type <item> match_op
 
+%type <labels> label_set
+%type <labelSet> label_set_list
+%type <label> label_set_item    
+
 %start start
 
 %%
 
 start           : START_LABELS label_matchers
                      {yylex.(*parser).generatedParserResult.(*VectorSelector).LabelMatchers = $2}
-                | error 
-                        { yylex.(*parser).errorf("unknown syntax error after parsing %v", yylex.(*parser).token.desc()) }
+                | START_LABEL_SET label_set
+                     { yylex.(*parser).generatedParserResult = $2 }
+                | error /* If none of the more detailed error messages are triggered, we fall back to this. */
+                        { yylex.(*parser).errorf("unexpected %v", yylex.(*parser).token.desc()) }
                 ;
 
 
+label_matchers  : 
+                LEFT_BRACE label_match_list RIGHT_BRACE
+                        { $$ = $2 }
+                | LEFT_BRACE label_match_list COMMA RIGHT_BRACE
+                        { $$ = $2 }
+                | LEFT_BRACE RIGHT_BRACE
+                        { $$ = []*labels.Matcher{} }
+
+                ;
+
 label_match_list:
                 label_match_list COMMA label_matcher
                         { $$ = append($1, $3)}
                 | label_matcher
                         { $$ = []*labels.Matcher{$1}}
-                ;
-
-label_matchers  : 
-                LEFT_BRACE label_match_list RIGHT_BRACE
-                        { $$ = $2 }
-                | LEFT_BRACE RIGHT_BRACE
-                        { $$ = []*labels.Matcher{} }
-
+                | label_match_list error
+                        { yylex.(*parser).errorf("unexpected %v in label matching, expected \",\" or \"}\"", yylex.(*parser).token.desc()) }
                 ;
 
 label_matcher   :
@@ -140,6 +154,10 @@ label_matcher   :
                         { $$ = yylex.(*parser).newLabelMatcher($1, $2, $3) }
                 | IDENTIFIER match_op error
                         { yylex.(*parser).errorf("unexpected %v in label matching, expected string", yylex.(*parser).token.desc())}
+                | IDENTIFIER error 
+                        { yylex.(*parser).errorf("unexpected %v in label matching, expected label matching operator", yylex.(*parser).token.Val) } 
+                | error
+                        { yylex.(*parser).errorf("unexpected %v in label matching, expected identifier or \"}\"", yylex.(*parser).token.desc()) }
                 ;
 
 match_op        :
@@ -147,9 +165,39 @@ match_op        :
                 | NEQ {$$=$1}
                 | EQL_REGEX {$$=$1}
                 | NEQ_REGEX {$$=$1}
-                | error 
-                        { yylex.(*parser).errorf("expected label matching operator but got %s", yylex.(*parser).token.Val) } 
                 ;
 
+label_set       :
+                LEFT_BRACE label_set_list RIGHT_BRACE
+                        { $$ = labels.New($2...) }
+                | LEFT_BRACE label_set_list COMMA RIGHT_BRACE
+                        { $$ = labels.New($2...) }
+                | LEFT_BRACE RIGHT_BRACE
+                        { $$ = labels.New() }
+                ;
+
+label_set_list  :
+                label_set_list COMMA label_set_item
+                        { $$ = append($1, $3) }
+                | label_set_item
+                        { $$ = []labels.Label{$1} }
+                | label_set_list error
+                        { yylex.(*parser).errorf("unexpected %v in label set, expected \",\" or \"}\"", yylex.(*parser).token.desc()) }
+                
+                ;
+
+label_set_item  :
+                IDENTIFIER EQL STRING
+                        { $$ = labels.Label{Name: $1.Val, Value: yylex.(*parser).unquoteString($3.Val) } } 
+                | IDENTIFIER EQL error
+                        { yylex.(*parser).errorf("unexpected %v in label set, expected string", yylex.(*parser).token.desc())}
+                | IDENTIFIER error
+                        { yylex.(*parser).errorf("unexpected %v in label set, expected \"=\"", yylex.(*parser).token.desc())}
+                | error
+                        { yylex.(*parser).errorf("unexpected %v in label set, expected identifier or \"}\"", yylex.(*parser).token.desc()) }
+                ;
+
+                
+
 
 %%
diff --git a/promql/generated_parser.y.go b/promql/generated_parser.y.go
index 34176f8f11..cd5016699d 100644
--- a/promql/generated_parser.y.go
+++ b/promql/generated_parser.y.go
@@ -18,6 +18,9 @@ type yySymType struct {
 	item     Item
 	matchers []*labels.Matcher
 	matcher  *labels.Matcher
+	labelSet []labels.Label
+	label    labels.Label
+	labels   labels.Labels
 }
 
 const ERROR = 57346
@@ -85,7 +88,8 @@ const BOOL = 57407
 const keywordsEnd = 57408
 const startSymbolsStart = 57409
 const START_LABELS = 57410
-const startSymbolsEnd = 57411
+const START_LABEL_SET = 57411
+const startSymbolsEnd = 57412
 
 var yyToknames = [...]string{
 	"$end",
@@ -156,6 +160,7 @@ var yyToknames = [...]string{
 	"keywordsEnd",
 	"startSymbolsStart",
 	"START_LABELS",
+	"START_LABEL_SET",
 	"startSymbolsEnd",
 }
 var yyStatenames = [...]string{}
@@ -164,7 +169,7 @@ const yyEofCode = 1
 const yyErrCode = 2
 const yyInitialStackSize = 16
 
-//line promql/generated_parser.y:155
+//line promql/generated_parser.y:203
 
 //line yacctab:1
 var yyExca = [...]int{
@@ -175,49 +180,57 @@ var yyExca = [...]int{
 
 const yyPrivate = 57344
 
-const yyLast = 67
+const yyLast = 68
 
 var yyAct = [...]int{
 
-	3, 17, 20, 11, 9, 5, 10, 8, 9, 7,
-	1, 12, 6, 4, 0, 0, 0, 0, 18, 19,
+	4, 23, 16, 32, 11, 40, 36, 30, 21, 18,
+	1, 8, 14, 6, 17, 7, 22, 28, 19, 37,
+	29, 20, 39, 35, 9, 34, 13, 5, 0, 0,
+	0, 12, 38, 24, 25, 31, 33, 18, 13, 26,
+	27, 0, 17, 12, 0, 0, 0, 15, 10, 0,
 	0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 0, 13, 14, 0, 0, 0, 0, 15,
-	16, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
-	0, 0, 0, 0, 0, 0, 2,
+	0, 0, 0, 0, 0, 0, 2, 3,
 }
 var yyPact = [...]int{
 
-	-2, -1000, -6, -1000, -1000, -3, -9, -1000, -1000, -1,
-	1, -1000, 0, -1000, -1000, -1000, -1000, -1000, -1000, -1000,
+	-2, -1000, 2, 0, -1000, -1000, 36, -1000, 35, 6,
+	-1000, -1000, -1, -1000, 5, -1000, -1000, 1, -1000, -1000,
+	24, -1000, 4, -1000, -1000, -1000, -1000, -1000, -1000, 7,
+	-1000, 3, -1000, -1000, -1000, -1000, -1000, -1000, -1000, -1000,
 	-1000,
 }
 var yyPgo = [...]int{
 
-	0, 13, 12, 7, 11, 10,
+	0, 27, 24, 4, 16, 15, 12, 2, 10,
 }
 var yyR1 = [...]int{
 
-	0, 5, 5, 2, 2, 1, 1, 3, 3, 4,
-	4, 4, 4, 4,
+	0, 8, 8, 8, 1, 1, 1, 2, 2, 2,
+	3, 3, 3, 3, 4, 4, 4, 4, 5, 5,
+	5, 6, 6, 6, 7, 7, 7, 7,
 }
 var yyR2 = [...]int{
 
-	0, 2, 1, 3, 1, 3, 2, 3, 3, 1,
-	1, 1, 1, 1,
+	0, 2, 2, 1, 3, 4, 2, 3, 1, 2,
+	3, 3, 2, 1, 1, 1, 1, 1, 3, 4,
+	2, 3, 1, 2, 3, 3, 2, 1,
 }
 var yyChk = [...]int{
 
-	-1000, -5, 68, 2, -1, 11, -2, 12, -3, 7,
-	15, 12, -4, 34, 35, 40, 41, 2, -3, 19,
+	-1000, -8, 68, 69, 2, -1, 11, -5, 11, -2,
+	12, -3, 7, 2, -6, 12, -7, 7, 2, 12,
+	15, 2, -4, 2, 34, 35, 40, 41, 12, 15,
+	2, 34, 2, 12, -3, 19, 2, 12, -7, 19,
 	2,
 }
 var yyDef = [...]int{
 
-	0, -2, 0, 2, 1, 0, 0, 6, 4, 0,
-	0, 5, 0, 9, 10, 11, 12, 13, 3, 7,
-	8,
+	0, -2, 0, 0, 3, 1, 0, 2, 0, 0,
+	6, 8, 0, 13, 0, 20, 22, 0, 27, 4,
+	0, 9, 0, 12, 14, 15, 16, 17, 18, 0,
+	23, 0, 26, 5, 7, 10, 11, 19, 21, 24,
+	25,
 }
 var yyTok1 = [...]int{
 
@@ -231,7 +244,7 @@ var yyTok2 = [...]int{
 	32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
 	42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
 	52, 53, 54, 55, 56, 57, 58, 59, 60, 61,
-	62, 63, 64, 65, 66, 67, 68, 69,
+	62, 63, 64, 65, 66, 67, 68, 69, 70,
 }
 var yyTok3 = [...]int{
 	0,
@@ -576,81 +589,165 @@ yydefault:
 
 	case 1:
 		yyDollar = yyS[yypt-2 : yypt+1]
-//line promql/generated_parser.y:117
+//line promql/generated_parser.y:125
 		{
 			yylex.(*parser).generatedParserResult.(*VectorSelector).LabelMatchers = yyDollar[2].matchers
 		}
 	case 2:
-		yyDollar = yyS[yypt-1 : yypt+1]
-//line promql/generated_parser.y:119
-		{
-			yylex.(*parser).errorf("unknown syntax error after parsing %v", yylex.(*parser).token.desc())
-		}
-	case 3:
-		yyDollar = yyS[yypt-3 : yypt+1]
-//line promql/generated_parser.y:125
-		{
-			yyVAL.matchers = append(yyDollar[1].matchers, yyDollar[3].matcher)
-		}
-	case 4:
-		yyDollar = yyS[yypt-1 : yypt+1]
+		yyDollar = yyS[yypt-2 : yypt+1]
 //line promql/generated_parser.y:127
 		{
-			yyVAL.matchers = []*labels.Matcher{yyDollar[1].matcher}
+			yylex.(*parser).generatedParserResult = yyDollar[2].labels
+		}
+	case 3:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:129
+		{
+			yylex.(*parser).errorf("unexpected %v", yylex.(*parser).token.desc())
+		}
+	case 4:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:135
+		{
+			yyVAL.matchers = yyDollar[2].matchers
 		}
 	case 5:
-		yyDollar = yyS[yypt-3 : yypt+1]
-//line promql/generated_parser.y:132
+		yyDollar = yyS[yypt-4 : yypt+1]
+//line promql/generated_parser.y:137
 		{
 			yyVAL.matchers = yyDollar[2].matchers
 		}
 	case 6:
 		yyDollar = yyS[yypt-2 : yypt+1]
-//line promql/generated_parser.y:134
+//line promql/generated_parser.y:139
 		{
 			yyVAL.matchers = []*labels.Matcher{}
 		}
 	case 7:
 		yyDollar = yyS[yypt-3 : yypt+1]
-//line promql/generated_parser.y:140
+//line promql/generated_parser.y:145
 		{
-			yyVAL.matcher = yylex.(*parser).newLabelMatcher(yyDollar[1].item, yyDollar[2].item, yyDollar[3].item)
+			yyVAL.matchers = append(yyDollar[1].matchers, yyDollar[3].matcher)
 		}
 	case 8:
-		yyDollar = yyS[yypt-3 : yypt+1]
-//line promql/generated_parser.y:142
-		{
-			yylex.(*parser).errorf("unexpected %v in label matching, expected string", yylex.(*parser).token.desc())
-		}
-	case 9:
-		yyDollar = yyS[yypt-1 : yypt+1]
-//line promql/generated_parser.y:146
-		{
-			yyVAL.item = yyDollar[1].item
-		}
-	case 10:
 		yyDollar = yyS[yypt-1 : yypt+1]
 //line promql/generated_parser.y:147
 		{
-			yyVAL.item = yyDollar[1].item
+			yyVAL.matchers = []*labels.Matcher{yyDollar[1].matcher}
 		}
-	case 11:
-		yyDollar = yyS[yypt-1 : yypt+1]
-//line promql/generated_parser.y:148
-		{
-			yyVAL.item = yyDollar[1].item
-		}
-	case 12:
-		yyDollar = yyS[yypt-1 : yypt+1]
+	case 9:
+		yyDollar = yyS[yypt-2 : yypt+1]
 //line promql/generated_parser.y:149
 		{
-			yyVAL.item = yyDollar[1].item
+			yylex.(*parser).errorf("unexpected %v in label matching, expected \",\" or \"}\"", yylex.(*parser).token.desc())
+		}
+	case 10:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:154
+		{
+			yyVAL.matcher = yylex.(*parser).newLabelMatcher(yyDollar[1].item, yyDollar[2].item, yyDollar[3].item)
+		}
+	case 11:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:156
+		{
+			yylex.(*parser).errorf("unexpected %v in label matching, expected string", yylex.(*parser).token.desc())
+		}
+	case 12:
+		yyDollar = yyS[yypt-2 : yypt+1]
+//line promql/generated_parser.y:158
+		{
+			yylex.(*parser).errorf("unexpected %v in label matching, expected label matching operator", yylex.(*parser).token.Val)
 		}
 	case 13:
 		yyDollar = yyS[yypt-1 : yypt+1]
-//line promql/generated_parser.y:151
+//line promql/generated_parser.y:160
 		{
-			yylex.(*parser).errorf("expected label matching operator but got %s", yylex.(*parser).token.Val)
+			yylex.(*parser).errorf("unexpected %v in label matching, expected identifier or \"}\"", yylex.(*parser).token.desc())
+		}
+	case 14:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:164
+		{
+			yyVAL.item = yyDollar[1].item
+		}
+	case 15:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:165
+		{
+			yyVAL.item = yyDollar[1].item
+		}
+	case 16:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:166
+		{
+			yyVAL.item = yyDollar[1].item
+		}
+	case 17:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:167
+		{
+			yyVAL.item = yyDollar[1].item
+		}
+	case 18:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:172
+		{
+			yyVAL.labels = labels.New(yyDollar[2].labelSet...)
+		}
+	case 19:
+		yyDollar = yyS[yypt-4 : yypt+1]
+//line promql/generated_parser.y:174
+		{
+			yyVAL.labels = labels.New(yyDollar[2].labelSet...)
+		}
+	case 20:
+		yyDollar = yyS[yypt-2 : yypt+1]
+//line promql/generated_parser.y:176
+		{
+			yyVAL.labels = labels.New()
+		}
+	case 21:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:181
+		{
+			yyVAL.labelSet = append(yyDollar[1].labelSet, yyDollar[3].label)
+		}
+	case 22:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:183
+		{
+			yyVAL.labelSet = []labels.Label{yyDollar[1].label}
+		}
+	case 23:
+		yyDollar = yyS[yypt-2 : yypt+1]
+//line promql/generated_parser.y:185
+		{
+			yylex.(*parser).errorf("unexpected %v in label set, expected \",\" or \"}\"", yylex.(*parser).token.desc())
+		}
+	case 24:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:191
+		{
+			yyVAL.label = labels.Label{Name: yyDollar[1].item.Val, Value: yylex.(*parser).unquoteString(yyDollar[3].item.Val)}
+		}
+	case 25:
+		yyDollar = yyS[yypt-3 : yypt+1]
+//line promql/generated_parser.y:193
+		{
+			yylex.(*parser).errorf("unexpected %v in label set, expected string", yylex.(*parser).token.desc())
+		}
+	case 26:
+		yyDollar = yyS[yypt-2 : yypt+1]
+//line promql/generated_parser.y:195
+		{
+			yylex.(*parser).errorf("unexpected %v in label set, expected \"=\"", yylex.(*parser).token.desc())
+		}
+	case 27:
+		yyDollar = yyS[yypt-1 : yypt+1]
+//line promql/generated_parser.y:197
+		{
+			yylex.(*parser).errorf("unexpected %v in label set, expected identifier or \"}\"", yylex.(*parser).token.desc())
 		}
 	}
 	goto yystack /* stack new state and value */
diff --git a/promql/parse.go b/promql/parse.go
index 4862976240..42cccfaea8 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -41,7 +41,7 @@ type parser struct {
 
 	switchSymbols []ItemType
 
-	generatedParserResult Node
+	generatedParserResult interface{}
 }
 
 // ParseErr wraps a parsing error with line and position context.
@@ -801,90 +801,7 @@ func (p *parser) call(name string) *Call {
 //		'{' [ <labelname> '=' <match_string>, ... ] '}'
 //
 func (p *parser) labelSet() labels.Labels {
-	set := []labels.Label{}
-	for _, lm := range p.labelMatchers(EQL) {
-		set = append(set, labels.Label{Name: lm.Name, Value: lm.Value})
-	}
-	return labels.New(set...)
-}
-
-// labelMatchers parses a set of label matchers.
-//
-//		'{' [ <labelname> <match_op> <match_string>, ... ] '}'
-//
-func (p *parser) labelMatchers(operators ...ItemType) []*labels.Matcher {
-	const ctx = "label matching"
-
-	matchers := []*labels.Matcher{}
-
-	p.expect(LEFT_BRACE, ctx)
-
-	// Check if no matchers are provided.
-	if p.peek().Typ == RIGHT_BRACE {
-		p.next()
-		return matchers
-	}
-
-	for {
-		label := p.expect(IDENTIFIER, ctx)
-
-		op := p.next().Typ
-		if !op.isOperator() {
-			p.errorf("expected label matching operator but got %s", op)
-		}
-		var validOp = false
-		for _, allowedOp := range operators {
-			if op == allowedOp {
-				validOp = true
-			}
-		}
-		if !validOp {
-			p.errorf("operator must be one of %q, is %q", operators, op)
-		}
-
-		val := p.unquoteString(p.expect(STRING, ctx).Val)
-
-		// Map the Item to the respective match type.
-		var matchType labels.MatchType
-		switch op {
-		case EQL:
-			matchType = labels.MatchEqual
-		case NEQ:
-			matchType = labels.MatchNotEqual
-		case EQL_REGEX:
-			matchType = labels.MatchRegexp
-		case NEQ_REGEX:
-			matchType = labels.MatchNotRegexp
-		default:
-			p.errorf("Item %q is not a metric match type", op)
-		}
-
-		m, err := labels.NewMatcher(matchType, label.Val, val)
-		if err != nil {
-			p.error(err)
-		}
-
-		matchers = append(matchers, m)
-
-		if p.peek().Typ == IDENTIFIER {
-			p.errorf("missing comma before next identifier %q", p.peek().Val)
-		}
-
-		// Terminate list if last matcher.
-		if p.peek().Typ != COMMA {
-			break
-		}
-		p.next()
-
-		// Allow comma after each Item in a multi-line listing.
-		if p.peek().Typ == RIGHT_BRACE {
-			break
-		}
-	}
-
-	p.expect(RIGHT_BRACE, ctx)
-
-	return matchers
+	return p.parseGenerated(START_LABEL_SET, []ItemType{RIGHT_BRACE, EOF}).(labels.Labels)
 }
 
 // metric parses a metric.
@@ -1141,7 +1058,7 @@ func parseDuration(ds string) (time.Duration, error) {
 // The generated parser will consume the lexer Stream until one of the
 // tokens listed in switchSymbols is encountered. switchSymbols
 // should at least contain EOF
-func (p *parser) parseGenerated(startSymbol ItemType, switchSymbols []ItemType) Node {
+func (p *parser) parseGenerated(startSymbol ItemType, switchSymbols []ItemType) interface{} {
 	p.InjectItem(startSymbol)
 
 	p.switchSymbols = switchSymbols
diff --git a/promql/parse_test.go b/promql/parse_test.go
index ae3b4bf69a..ff2a356da3 100644
--- a/promql/parse_test.go
+++ b/promql/parse_test.go
@@ -882,6 +882,19 @@ var testExpr = []struct {
 				mustLabelMatcher(labels.MatchEqual, string(model.MetricNameLabel), "foo"),
 			},
 		},
+	}, {
+		input: `foo{a="b", foo!="bar", test=~"test", bar!~"baz",}`,
+		expected: &VectorSelector{
+			Name:   "foo",
+			Offset: 0,
+			LabelMatchers: []*labels.Matcher{
+				mustLabelMatcher(labels.MatchEqual, "a", "b"),
+				mustLabelMatcher(labels.MatchNotEqual, "foo", "bar"),
+				mustLabelMatcher(labels.MatchRegexp, "test", "test"),
+				mustLabelMatcher(labels.MatchNotRegexp, "bar", "baz"),
+				mustLabelMatcher(labels.MatchEqual, string(model.MetricNameLabel), "foo"),
+			},
+		},
 	}, {
 		input:  `{`,
 		fail:   true,
@@ -923,7 +936,7 @@ var testExpr = []struct {
 	}, {
 		input:  `foo{gibberish}`,
 		fail:   true,
-		errMsg: "expected label matching operator but got }",
+		errMsg: "unexpected } in label matching, expected label matching operator",
 	}, {
 		input:  `foo{1}`,
 		fail:   true,
@@ -951,7 +964,23 @@ var testExpr = []struct {
 	}, {
 		input:  `foo{__name__="bar"}`,
 		fail:   true,
-		errMsg: "metric name must not be set twice: \"foo\" or \"bar\"",
+		errMsg: `metric name must not be set twice: "foo" or "bar"`,
+	}, {
+		input:  `foo{__name__= =}`,
+		fail:   true,
+		errMsg: "unexpected <op:=> in label matching, expected string",
+	}, {
+		input:  `foo{,}`,
+		fail:   true,
+		errMsg: `unexpected "," in label matching, expected identifier or "}"`,
+	}, {
+		input:  `foo{__name__ == "bar"}`,
+		fail:   true,
+		errMsg: "unexpected <op:=> in label matching, expected string",
+	}, {
+		input:  `foo{__name__="bar" lol}`,
+		fail:   true,
+		errMsg: `unexpected identifier "lol" in label matching, expected "," or "}"`,
 	},
 	// Test matrix selector.
 	{
@@ -1606,7 +1635,7 @@ func TestParseExpressions(t *testing.T) {
 			testutil.Equals(t, expr, test.expected, "error on input '%s'", test.input)
 		} else {
 			testutil.NotOk(t, err)
-			testutil.Assert(t, strings.Contains(err.Error(), test.errMsg), "unexpected error on input '%s'", test.input)
+			testutil.Assert(t, strings.Contains(err.Error(), test.errMsg), "unexpected error on input '%s', expected '%s', got '%s'", test.input, test.errMsg, err.Error())
 		}
 	}
 }