From 4d97205f723957414be9d20e7669f8958196f954 Mon Sep 17 00:00:00 2001
From: psteinroe <philipp@steinroetter.com>
Date: Fri, 13 Oct 2023 17:10:20 +0200
Subject: [PATCH] chore: add comments

---
 crates/parser/src/lib.rs              |  8 ++++----
 crates/parser/src/statement_parser.rs | 15 ++++++++++-----
 crates/parser/src/syntax_error.rs     |  2 +-
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/crates/parser/src/lib.rs b/crates/parser/src/lib.rs
index 493b49cb..2a24b634 100644
--- a/crates/parser/src/lib.rs
+++ b/crates/parser/src/lib.rs
@@ -3,17 +3,17 @@
 //! This crate provides a parser for the Postgres SQL dialect.
 //! It is based in the pg_query.rs crate, which is a wrapper around the PostgreSQL query parser.
 //! The main `Parser` struct parses a source file and individual statements.
-//! The `Parse` struct contains the resulting concrete syntax tree, syntax errors, and the abtract syntax tree, which is a list of pg_query statements and their positions.
+//! The `Parse` result struct contains the resulting concrete syntax tree, syntax errors, and the abtract syntax tree, which is a list of pg_query statements and their positions.
 //!
 //! The idea is to offload the heavy lifting to the same parser that the PostgreSQL server uses,
-//! and just fill in the gaps to be able to build both cst and ast from a a source file that
+//! and just fill in the gaps to be able to build both cst and ast from a source file that
 //! potentially contains erroneous statements.
 //!
 //! The main drawbacks of the PostgreSQL query parser mitigated by this parser are:
 //! - it only parsed a full source text, and if there is any syntax error in a file, it will not parse anything and return an error.
-//! - it does not parse whitespaces and newlines, so it is not possible to build a concrete syntax tree build a concrete syntax tree.
+//! - it does not parse whitespaces and newlines, and it only returns ast nodes. The concrete syntax tree has to be reverse-engineered.
 //!
-//! To see how these drawbacks are mitigated, see the `statement.rs` and the `source_file.rs` module.
+//! To see how these drawbacks are mitigated, see the `statement_parser.rs` and the `source_parser.rs` module.
 
 mod ast_node;
 mod estimate_node_range;
diff --git a/crates/parser/src/statement_parser.rs b/crates/parser/src/statement_parser.rs
index 46e7126d..25d35511 100644
--- a/crates/parser/src/statement_parser.rs
+++ b/crates/parser/src/statement_parser.rs
@@ -9,10 +9,7 @@ use crate::{
     syntax_kind_codegen::SyntaxKind,
 };
 
-/// A super simple lexer for sql statements.
-///
-/// One weakness of pg_query.rs is that it does not parse whitespace or newlines. We use a very
-/// simple lexer to fill the gaps.
+/// Super simple lexer that only catches the tokens that libpg_query ignores.
 #[derive(Logos, Debug, PartialEq)]
 pub enum StatementToken {
     // comments and whitespaces
@@ -27,7 +24,7 @@ pub enum StatementToken {
 }
 
 impl StatementToken {
-    /// Creates a `SyntaxKind` from a `StatementToken`.
+    /// Create a `SyntaxKind` from a `StatementToken`.
     pub fn syntax_kind(&self) -> SyntaxKind {
         match self {
             StatementToken::Whitespace => SyntaxKind::Whitespace,
@@ -39,6 +36,13 @@ impl StatementToken {
 }
 
 impl Parser {
+    /// Parse a single statement passed in `text`. If `at_offset` is `Some`, the statement is assumed to be at that offset in the source file.
+    ///
+    /// On a high level, the parser works as follows:
+    /// - 1. Collect all information from pg_query.rs and `StatementToken` lexer
+    /// - 2. Derive as much information as possible from the collected information
+    /// - 3. Collect AST node and errors, if any
+    /// - 3. Walk the statement token by token, and reverse-engineer the concrete syntax tree
     pub fn parse_statement_at(&mut self, text: &str, at_offset: Option<u32>) {
         // 1. Collect as much information as possible from pg_query.rs and `StatementToken` lexer
 
@@ -98,6 +102,7 @@ impl Parser {
         let mut statement_token_lexer = StatementToken::lexer(&text);
 
         // 2. Setup data structures required for the parsing algorithm
+
         // A buffer for tokens that are not applied immediately to the cst
         let mut token_buffer: VecDeque<(SyntaxKind, String)> = VecDeque::new();
         // Keeps track of currently open nodes. Latest opened is last.
diff --git a/crates/parser/src/syntax_error.rs b/crates/parser/src/syntax_error.rs
index d8dee689..df6d670f 100644
--- a/crates/parser/src/syntax_error.rs
+++ b/crates/parser/src/syntax_error.rs
@@ -2,7 +2,7 @@ use std::fmt;
 
 use cstree::text::{TextRange, TextSize};
 
-/// Represents the result of unsuccessful tokenization, parsing
+/// Represents the result of unsuccessful tokenization, parsing,
 /// or tree validation.
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct SyntaxError(String, TextRange);