text/template: rename depth variables

Renames parenDepth to stackDepth and maxExpressionParenDepth
to maxStackDepth to better reflect their purpose in preventing
stack overflow. Also simplifies initialization logic and improves
comment clarity per PR feedback.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

Author: thevilledev

src/text/template/parse/parse.go

@@ -32,7 +32,7 @@ type Tree struct {
 	treeSet    map[string]*Tree
 	actionLine int // line of left delim starting action
 	rangeDepth int
-	parenDepth int // depth of nested parenthesized expressions
+	stackDepth int // depth of nested parenthesized expressions
 }
 
 // A mode value is a set of flags (or 0). Modes control parser behavior.
@@ -43,17 +43,14 @@ const (
 	SkipFuncCheck                  // do not check that functions are defined
 )
 
-// maxExpressionParenDepth is the maximum depth permitted for nested
+// maxStackDepth is the maximum depth permitted for nested
 // parenthesized expressions.
-var maxExpressionParenDepth int
+var maxStackDepth = 10000
 
-// init sets up the maximum expression parenthesis depth based on the architecture.
-// WebAssembly has a smaller stack size and is more prone to stack overflow.
+// init reduces maxStackDepth for WebAssembly due to its smaller stack size.
 func init() {
 	if runtime.GOARCH == "wasm" {
-		maxExpressionParenDepth = 1000
-	} else {
-		maxExpressionParenDepth = 10000
+		maxStackDepth = 1000
 	}
 }
 
@@ -238,7 +235,7 @@ func (t *Tree) startParse(funcs []map[string]any, lex *lexer, treeSet map[string
 	t.vars = []string{"$"}
 	t.funcs = funcs
 	t.treeSet = treeSet
-	t.parenDepth = 0
+	t.stackDepth = 0
 	lex.options = lexOptions{
 		emitComment: t.Mode&ParseComments != 0,
 		breakOK:     !t.hasFunction("break"),
@@ -803,11 +800,11 @@ func (t *Tree) term() Node {
 		}
 		return number
 	case itemLeftParen:
-		if t.parenDepth >= maxExpressionParenDepth {
+		if t.stackDepth >= maxStackDepth {
 			t.errorf("max expression depth exceeded")
 		}
-		t.parenDepth++
-		defer func() { t.parenDepth-- }()
+		t.stackDepth++
+		defer func() { t.stackDepth-- }()
 		return t.pipeline("parenthesized pipeline", itemRightParen)
 	case itemString, itemRawString:
 		s, err := strconv.Unquote(token.val)

src/text/template/parse/parse_test.go

@@ -87,8 +87,8 @@ var numberTests = []numberTest{
 }
 
 func init() {
-	// Use a small depth limit for testing to avoid creating huge expressions.
-	maxExpressionParenDepth = 3
+	// Use a small stack limit for testing to avoid creating huge expressions.
+	maxStackDepth = 3
 }
 
 func TestNumberParse(t *testing.T) {
@@ -333,7 +333,7 @@ var parseTests = []parseTest{
 	// Missing pipeline in block
 	{"block definition", `{{block "foo"}}hello{{end}}`, hasError, ""},
 
-	// Parenthesis nesting depth tests
+	// Expression nested depth tests.
 	{"paren nesting normal", "{{ (( 1 )) }}", noError, "{{((1))}}"},
 	{"paren nesting at limit", "{{ ((( 1 ))) }}", noError, "{{(((1)))}}"},
 	{"paren nesting exceeds limit", "{{ (((( 1 )))) }}", hasError, "template: test:1: max expression depth exceeded"},