From c6b11a8f90760175d9a30486210eeffd30ee6eb2 Mon Sep 17 00:00:00 2001
From: Kyle Brandt <kyle@grafana.com>
Date: Mon, 14 Dec 2020 14:21:16 -0500
Subject: [PATCH] Expressions: support ${my var} syntax (#29819)

---
 pkg/expr/mathexp/parse/lex.go      | 25 +++++++++++++++++++++----
 pkg/expr/mathexp/parse/lex_test.go | 13 +++++++++++++
 pkg/expr/mathexp/parse/node.go     |  2 +-
 pkg/expr/mathexp/parse/parse.go    |  5 +++--
 4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/pkg/expr/mathexp/parse/lex.go b/pkg/expr/mathexp/parse/lex.go
index 99ca63e004e..fc48211a741 100644
--- a/pkg/expr/mathexp/parse/lex.go
+++ b/pkg/expr/mathexp/parse/lex.go
@@ -288,9 +288,29 @@ func lexFunc(l *lexer) stateFn {
 
 func lexVar(l *lexer) stateFn {
 	hasChar := false
+	if l.peek() == '{' {
+		_ = l.next()
+		for {
+			switch r := l.next(); {
+			case r == '}':
+				if !hasChar {
+					return l.errorf("incomplete variable")
+				}
+				l.emit(itemVar)
+				return lexItem
+			case r == eof:
+				return l.errorf("unterminated variable missing closing }")
+			case isVarchar(r) || isSpace(r):
+				hasChar = true
+			default:
+				return l.errorf("unsupported variable character")
+			}
+		}
+	}
+
 	for {
 		switch r := l.next(); {
-		case unicode.IsLetter(r):
+		case isVarchar(r):
 			hasChar = true
 			// absorb
 		default:
@@ -321,9 +341,6 @@ func isSpace(r rune) bool {
 	return unicode.IsSpace(r)
 }
 
-// isVarchar should maybe be used in place of unicode is letter above,
-// but do not want to modify it at this time, so adding lint exception.
-// nolint:unused,deadcode
 func isVarchar(r rune) bool {
 	return r == '_' || unicode.IsLetter(r) || unicode.IsDigit(r)
 }
diff --git a/pkg/expr/mathexp/parse/lex_test.go b/pkg/expr/mathexp/parse/lex_test.go
index 482815e2f98..e5b5ec59fc8 100644
--- a/pkg/expr/mathexp/parse/lex_test.go
+++ b/pkg/expr/mathexp/parse/lex_test.go
@@ -97,6 +97,16 @@ var lexTests = []lexTest{
 		{itemNumber, 0, "1.2e-4"},
 		tEOF,
 	}},
+	{"curly brace var", "${My Var}", []item{
+		{itemVar, 0, "${My Var}"},
+		tEOF,
+	}},
+	{"curly brace var plus 1", "${My Var} + 1", []item{
+		{itemVar, 0, "${My Var}"},
+		tPlus,
+		{itemNumber, 0, "1"},
+		tEOF,
+	}},
 	{"number plus var", "1 + $A", []item{
 		{itemNumber, 0, "1"},
 		tPlus,
@@ -113,6 +123,9 @@ var lexTests = []lexTest{
 	{"invalid var", "$", []item{
 		{itemError, 0, "incomplete variable"},
 	}},
+	{"invalid curly var", "${adf sd", []item{
+		{itemError, 0, "unterminated variable missing closing }"},
+	}},
 }
 
 // collect gathers the emitted items into a slice.
diff --git a/pkg/expr/mathexp/parse/node.go b/pkg/expr/mathexp/parse/node.go
index 79da348580a..711d0bf65e9 100644
--- a/pkg/expr/mathexp/parse/node.go
+++ b/pkg/expr/mathexp/parse/node.go
@@ -88,7 +88,7 @@ func (t NodeType) String() string {
 type VarNode struct {
 	NodeType
 	Pos
-	Name string // Without the $
+	Name string // Without the $ or {}
 	Text string // Raw
 }
 
diff --git a/pkg/expr/mathexp/parse/parse.go b/pkg/expr/mathexp/parse/parse.go
index ad2e75c37e1..4652390f29c 100644
--- a/pkg/expr/mathexp/parse/parse.go
+++ b/pkg/expr/mathexp/parse/parse.go
@@ -300,8 +300,9 @@ func (t *Tree) v() Node {
 func (t *Tree) Var() (v *VarNode) {
 	token := t.next()
 	varNoPrefix := strings.TrimPrefix(token.val, "$")
-	t.VarNames = append(t.VarNames, varNoPrefix)
-	return newVar(token.pos, varNoPrefix, token.val)
+	varNoBraces := strings.TrimSuffix(strings.TrimPrefix(varNoPrefix, "{"), "}")
+	t.VarNames = append(t.VarNames, varNoBraces)
+	return newVar(token.pos, varNoBraces, token.val)
 }
 
 // Func parses a FuncNode.