Possible to use less recursion when parsing?

[vpanteleev-sym]

Currently trying to parse a moderately sized GraphQL schema at compile-time results in:

.../source/graphql/lexer.d(66,15): Error: function `graphql.lexer.Lexer.eatComment` CTFE recursion limit exceeded
.../source/graphql/lexer.d(88,22):        called from here: `this.eatComment()`
.../source/graphql/lexer.d(104,21):        called from here: `this.eatWhitespace()`
.../source/graphql/lexer.d(548,18):        called from here: `this.buildToken()`
.../source/graphql/parser.d(2153,21):        called from here: `this.lex.popFront()`
.../source/graphql/parser.d(2140,33):        called from here: `this.parseListTypeImpl()`
.../source/graphql/parser.d(2108,38):        called from here: `this.parseListType()`
.../source/graphql/parser.d(2081,29):        called from here: `this.parseTypeImpl()`
.../source/graphql/parser.d(3947,33):        called from here: `this.parseType()`
.../source/graphql/parser.d(3861,45):        called from here: `this.parseInputValueDefinitionImpl()`
.../source/graphql/parser.d(3805,60):        called from here: `this.parseInputValueDefinition()`
.../source/graphql/parser.d(3792,46):        called from here: `this.parseInputValueDefinitionsImpl()`
.../source/graphql/parser.d(3801,24):        9 recursive calls to function `parseInputValueDefinitionsImpl`
.../source/graphql/parser.d(3790,24):        recursively called from function `parseInputValueDefinitions`
.../source/graphql/parser.d(5022,67):        called from here: `this.parseInputValueDefinitions()`
.../source/graphql/parser.d(4946,50):        called from here: `this.parseInputObjectTypeDefinitionImpl()`
.../source/graphql/parser.d(2670,71):        called from here: `this.parseInputObjectTypeDefinition()`
.../source/graphql/parser.d(2627,39):        called from here: `this.parseTypeDefinitionImpl()`
.../source/graphql/parser.d(2570,49):        called from here: `this.parseTypeDefinition()`
.../source/graphql/parser.d(2523,45):        called from here: `this.parseTypeSystemDefinitionImpl()`
.../source/graphql/parser.d(142,62):        called from here: `this.parseTypeSystemDefinition()`
.../source/graphql/parser.d(117,35):        called from here: `this.parseDefinitionImpl()`
.../source/graphql/parser.d(82,41):        called from here: `this.parseDefinition()`
.../source/graphql/parser.d(69,36):        called from here: `this.parseDefinitionsImpl()`
.../source/graphql/parser.d(78,14):        479 recursive calls to function `parseDefinitionsImpl`
.../source/graphql/parser.d(67,14):        recursively called from function `parseDefinitions`
.../source/graphql/parser.d(44,44):        called from here: `this.parseDefinitions()`
.../source/graphql/parser.d(31,33):        called from here: `this.parseDocumentImpl()`
.../source/graphql/client/query.d(66,27):        called from here: `p.parseDocument()`
.../source/graphql/client/query.d(69,3):        called from here: `(*function () @system => SchemaDocument(SchemaDefinition(null), null, null, null, null, null).this(d))()`
Error: cannot interpret `__error` at compile time
.../source/graphql/client/query.d(25,13):        called from here: `toD(document, settings)`
.../source/graphql/client/query.d(26,3):        called from here: `(*function () @system => toD(document, settings))()`
.../source/graphql/client/query.d(70,12): Error: template instance `graphql.client.query.GraphQLSchema!(document, GraphQLSettings

It looks like the root of the issue is that parseDefinitions recurses into itself (via parseDefinitionsImpl), so the parsed document size will always be limited by the maximum stack depth.

Looking at the generated code, at least for this case, it doesn't seem like recursion is strictly required, and can be replaced with a loop instead. Perhaps we can detect this situation in Darser and generate different code for it which avoids excessive recursion.