Add module-level doc comments to all printer submodules

Document the purpose and responsibilities of each submodule in the
printer directory: mod.rs (overview table), collect.rs (three-phase
pipeline), items.rs (Item construction), link_map.rs (function
resolution), mir_visitor.rs (body traversal), schema.rs (data model),
ty_visitor.rs (type collection), types.rs (TypeMetadata), and
util.rs (helpers).

Author: cds-amal

src/printer/collect.rs

@@ -1,3 +1,14 @@
+//! Three-phase collection pipeline.
+//!
+//! - [`collect_items`]: phase 1, enumerates monomorphized items from rustc
+//! - [`collect_and_analyze_items`]: phase 2, walks bodies with [`BodyAnalyzer`],
+//!   discovering transitive items through unevaluated constants
+//! - [`assemble_smir`]: phase 3, pure data transformation into [`SmirJson`]
+//!
+//! The phase boundary between 2 and 3 is enforced by types: `assemble_smir`
+//! receives [`CollectedCrate`] and [`DerivedInfo`], neither of which carries
+//! `Instance` or `MonoItem` handles, so it structurally cannot call `inst.body()`.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate rustc_span;

src/printer/items.rs

@@ -1,3 +1,10 @@
+//! Construction of [`Item`] values from monomorphized compiler items.
+//!
+//! Handles the mapping from `MonoItem` (function, static, or global asm) to the
+//! serializable [`Item`] structure, including optional debug-level details
+//! (instance kind, body pretty-print, generic parameters, internal type info)
+//! and foreign module enumeration.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate rustc_span;

src/printer/link_map.rs

@@ -1,3 +1,12 @@
+//! Link-time function resolution map.
+//!
+//! Maintains a mapping from function types (optionally qualified by instance kind)
+//! to their resolved symbol names. Entries are added from three sources:
+//! - `ITEM`: the function appears as a monomorphized item,
+//! - `TERM`: the function is called in a `Call` or `Drop` terminator,
+//! - `FPTR`: the function is referenced via a `ReifyFnPointer` cast or a
+//!   zero-sized FnDef constant.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate stable_mir;

src/printer/mir_visitor.rs

@@ -1,3 +1,17 @@
+//! MIR body traversal for collecting interned values.
+//!
+//! [`BodyAnalyzer`] implements `MirVisitor` and walks each function body exactly
+//! once, collecting:
+//! - function calls and drop glue into the link map
+//! - global allocations (memory, statics, vtables, function pointers) with
+//!   provenance type resolution via [`get_prov_ty`]
+//! - reachable types via the type visitor
+//! - source spans
+//!
+//! [`get_prov_ty`] recursively resolves the type of a pointer at a given byte
+//! offset within a struct or tuple, walking down through nested fields until it
+//! reaches the actual pointer type.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate rustc_span;

src/printer/mod.rs

@@ -1,3 +1,22 @@
+//! Serialization of Rust's Stable MIR to JSON.
+//!
+//! This module is the core of `stable-mir-json`: it collects monomorphized items,
+//! type metadata, allocations, and span information from the compiler, then
+//! serializes them into a [`SmirJson`] structure (emitted as `*.smir.json`).
+//!
+//! # Module structure
+//!
+//! | Module | Responsibility |
+//! |--------|----------------|
+//! | [`schema`] | Data model types ([`SmirJson`], [`Item`], [`AllocInfo`], etc.) and type aliases |
+//! | [`collect`] | Three-phase pipeline: collect items, analyze bodies, assemble final output |
+//! | [`items`] | Constructing [`Item`] values and extracting debug-level details |
+//! | [`mir_visitor`] | `BodyAnalyzer`: single-pass MIR traversal collecting calls, allocs, types, spans |
+//! | [`ty_visitor`] | Type visitor that recursively collects all reachable types with layout info |
+//! | [`link_map`] | Function resolution map: type + instance kind to symbol name |
+//! | [`types`] | Type helpers and [`TypeMetadata`](schema::TypeMetadata) construction |
+//! | [`util`] | Name resolution, attribute queries, and small collection utilities |
+
 use std::io::Write;
 use std::{fs::File, io};
 

src/printer/schema.rs

@@ -1,3 +1,9 @@
+//! Data model types for the `*.smir.json` output.
+//!
+//! Contains the top-level [`SmirJson`] structure and all supporting types:
+//! [`Item`], [`AllocMap`], [`AllocInfo`], [`TypeMetadata`], [`LinkMapKey`],
+//! [`FnSymType`], and serialization helpers.
+
 extern crate rustc_middle;
 extern crate serde;
 extern crate stable_mir;

src/printer/ty_visitor.rs

@@ -1,3 +1,10 @@
+//! Recursive type visitor for collecting reachable types with layout info.
+//!
+//! [`TyCollector`] implements `stable_mir::visitor::Visitor` and traverses
+//! type trees, recording each encountered type along with its `TyKind` and
+//! `LayoutShape`. The collected types are later transformed into
+//! [`TypeMetadata`](super::schema::TypeMetadata) entries in the final output.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate stable_mir;

src/printer/types.rs

@@ -1,3 +1,10 @@
+//! Type helpers and [`TypeMetadata`] construction.
+//!
+//! Provides utilities for working with `stable_mir` types: resolving function
+//! instances from types, checking for unresolved generics, and constructing
+//! [`TypeMetadata`](super::schema::TypeMetadata) entries from `TyKind` + layout
+//! for the final JSON output.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate stable_mir;

src/printer/util.rs

@@ -1,3 +1,5 @@
+//! Small helpers: name resolution, attribute queries, and collection utilities.
+
 extern crate rustc_middle;
 extern crate rustc_smir;
 extern crate rustc_span;