hclwrite: Format shouldn't introduce spaces before index brackets

This is another heuristic because the "[" syntax is also the tuple
constructor start marker, but this takes care of the common cases of
indexing keywords and bracketed expressions.

This fixes #29.

hclwrite/format.go

@@ -243,6 +243,9 @@ func spaceAfterToken(subject, before, after *Token) bool {
 		// No extra spaces within templates
 		return false
 
+	case after.Type == hclsyntax.TokenOBrack && (subject.Type == hclsyntax.TokenIdent || subject.Type == hclsyntax.TokenNumberLit || tokenBracketChange(subject) < 0):
+		return false
+
 	case subject.Type == hclsyntax.TokenMinus:
 		// Since a minus can either be subtraction or negation, and the latter
 		// should _not_ have a space after it, we need to use some heuristics

hclwrite/format_test.go

@@ -27,6 +27,18 @@ func TestFormat(t *testing.T) {
 			`a=b.c`,
 			`a = b.c`,
 		},
+		{
+			`a=b[c]`,
+			`a = b[c]`,
+		},
+		{
+			`a=b()[c]`,
+			`a = b()[c]`,
+		},
+		{
+			`a=["hello"][0]`,
+			`a = ["hello"][0]`,
+		},
 		{
 			`( a+2 )`,
 			`(a + 2)`,