syntax: allow bracket globs in array elements

Author: lawrence3699

syntax/filetests_test.go

@@ -4914,6 +4914,20 @@ var fileTests = []fileTestCase{
 			}},
 		}}}, LangBash),
 	),
+	fileTest(
+		[]string{`a=([i])`},
+		langFile(&CallExpr{Assigns: []*Assign{{
+			Name: lit("a"),
+			Array: arrValues(word(lit("[i]"))),
+		}}}, LangBash|LangZsh),
+	),
+	fileTest(
+		[]string{`a=("foo"[0-9])`},
+		langFile(&CallExpr{Assigns: []*Assign{{
+			Name: lit("a"),
+			Array: arrValues(word(dblQuoted(lit("foo")), lit("[0-9]"))),
+		}}}, LangBash|LangZsh),
+	),
 	fileTest(
 		[]string{"a]b"},
 		langFile(litStmt("a]b")),

syntax/lexer.go

@@ -325,7 +325,7 @@ skipSpace:
 			}
 			p.next()
 		case '[':
-			if p.quote == arrayElems {
+			if p.quote == arrayElems && p.arrayIndexAssign() {
 				p.rune()
 				p.tok = leftBrack
 			} else {
@@ -1066,6 +1066,54 @@ func (p *Parser) zshNumRange() bool {
 	return len(rest) > 0 && rest[0] == '>'
 }
 
+// arrayIndexAssign peeks ahead after a '[' in an array literal and reports
+// whether it begins an indexed assignment like [x]=y rather than a word that
+// happens to start with a bracket glob, like [0-9] or [[:space:]].
+func (p *Parser) arrayIndexAssign() bool {
+	rest := p.bs[p.bsp:]
+	depth := 1
+	var quote byte
+	escaped := false
+	for i, b := range rest {
+		if quote != 0 {
+			if escaped {
+				escaped = false
+				continue
+			}
+			if quote == '"' && b == '\\' {
+				escaped = true
+				continue
+			}
+			if b == quote {
+				quote = 0
+			}
+			continue
+		}
+		if escaped {
+			escaped = false
+			continue
+		}
+		switch b {
+		case '\\':
+			escaped = true
+		case '\'', '"':
+			quote = b
+		case '[':
+			depth++
+		case ']':
+			depth--
+			if depth == 0 {
+				return i+1 < len(rest) && rest[i+1] == '='
+			}
+		}
+	}
+	// If we can't find a matching closing bracket in the buffered input, keep the
+	// existing indexed-assignment tokenization and let the parser report any
+	// syntax errors. This keeps the lookahead conservative and avoids changing
+	// unrelated incomplete forms.
+	return true
+}
+
 func (p *Parser) advanceLitNone(r rune) {
 	p.eqlOffs = -1
 	tok := _LitWord

syntax/parser_test.go

@@ -1693,11 +1693,6 @@ var errorCases = []errorCase{
 		"a=([i)",
 		langErr("1:4: reached `)` without matching `[` with `]`", LangBash|LangZsh),
 	),
-	errCase(
-		"a=([i])",
-		langErr("1:4: `[x]` must be followed by `=`", LangBash|LangZsh),
-		flipConfirmAll, // TODO: why is this valid?
-	),
 	errCase(
 		"a[i]=(y)",
 		langErr("1:5: arrays cannot be nested", LangBash),