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Auto merge of #10653 - flip1995:book-type_passes_corrections, r=llogiq
Book: Improve type checking and lint passes chapters - Adds the lint passes chapter to the index. - Moves additional reading material for beginners to the front page of the development section. - Clarify some details in `hir::Ty` vs `ty::Ty`. `@blyxyas` I started reviewing the chapters that were already merged. Great work. I liked the additional reading chapter so much, that I moved it front and center. Other than that I only had some minor corrections to make. Please review. r? `@llogiq` changelog: none
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@ -13,6 +13,7 @@
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- [Development](development/README.md)
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- [Basics](development/basics.md)
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- [Adding Lints](development/adding_lints.md)
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- [Lint Passes](development/lint_passes.md)
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- [Type Checking](development/type_checking.md)
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- [Common Tools](development/common_tools_writing_lints.md)
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- [Infrastructure](development/infrastructure/README.md)
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@ -13,6 +13,24 @@ If this is your first time contributing to Clippy, you should first read the
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[Basics docs](basics.md). This will explain the basics on how to get the source
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code and how to compile and test the code.
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## Additional Readings for Beginners
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If a dear reader of this documentation has never taken a class on compilers
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and interpreters, it might be confusing as to why AST level deals with only
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the language's syntax. And some readers might not even understand what lexing,
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parsing, and AST mean.
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This documentation serves by no means as a crash course on compilers or language design.
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And for details specifically related to Rust, the [Rustc Development Guide][rustc_dev_guide]
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is a far better choice to peruse.
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The [Syntax and AST][ast] chapter and the [High-Level IR][hir] chapter are
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great introduction to the concepts mentioned in this chapter.
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Some readers might also find the [introductory chapter][map_of_territory] of
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Robert Nystrom's _Crafting Interpreters_ a helpful overview of compiled and
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interpreted languages before jumping back to the Rustc guide.
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## Writing code
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If you have done the basic setup, it's time to start hacking.
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@ -37,6 +55,10 @@ book](../lints.md).
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> - Triage procedure
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> - Bors and Homu
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[ast]: https://rustc-dev-guide.rust-lang.org/syntax-intro.html
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[hir]: https://rustc-dev-guide.rust-lang.org/hir.html
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[rustc_dev_guide]: https://rustc-dev-guide.rust-lang.org/
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[map_of_territory]: https://craftinginterpreters.com/a-map-of-the-territory.html
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[clippy_rfc]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md
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[rfc_stability]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#stability-guarantees
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[rfc_lint_cats]: https://github.com/rust-lang/rfcs/blob/master/text/2476-clippy-uno.md#lint-audit-and-categories
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@ -1,7 +1,7 @@
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# Lint passes
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Before working on the logic of a new lint, there is an important decision
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that every Clippy developers must make: to use
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that every Clippy developer must make: to use
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[`EarlyLintPass`][early_lint_pass] or [`LateLintPass`][late_lint_pass].
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In short, the `LateLintPass` has access to type and symbol information while the
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@ -107,30 +107,8 @@ that use `LateLintPass`:
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$ cargo dev new_lint --name=<your_new_lint> --pass=late --category=<your_category_choice>
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```
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## Additional Readings for Beginners
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If a dear reader of this documentation has never taken a class on compilers
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and interpreters, it might be confusing as to why AST level deals with only
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the language's syntax. And some readers might not even understand what lexing,
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parsing, and AST mean.
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This documentation serves by no means as a crash course on compilers or language design.
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And for details specifically related to Rust, the [Rustc Development Guide][rustc_dev_guide]
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is a far better choice to peruse.
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The [Syntax and AST][ast] chapter and the [High-Level IR][hir] chapter are
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great introduction to the concepts mentioned in this chapter.
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Some readers might also find the [introductory chapter][map_of_territory] of
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Robert Nystrom's _Crafting Interpreters_ a helpful overview of compiled and
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interpreted languages before jumping back to the Rustc guide.
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[ast]: https://rustc-dev-guide.rust-lang.org/syntax-intro.html
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[early_context]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/context/struct.EarlyContext.html
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[early_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.EarlyLintPass.html
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[hir]: https://rustc-dev-guide.rust-lang.org/hir.html
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[late_context]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/context/struct.LateContext.html
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[late_lint_pass]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/trait.LateLintPass.html
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[lexing_and_parsing]: https://rustc-dev-guide.rust-lang.org/overview.html#lexing-and-parsing
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[rustc_dev_guide]: https://rustc-dev-guide.rust-lang.org/
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[map_of_territory]: https://craftinginterpreters.com/a-map-of-the-territory.html
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@ -51,7 +51,7 @@ impl LateLintPass<'_> for MyStructLint {
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fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
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// Get type of `expr`
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let ty = cx.typeck_results().expr_ty(expr);
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// Check if the `Ty` of this expression is of character type
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if ty.is_char() {
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println!("Our expression is a char!");
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@ -70,18 +70,18 @@ pub fn is_char(self) -> bool {
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}
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```
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Indeed, we just discovered `Ty`'s [`kind` method][kind], which provides us
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Indeed, we just discovered `Ty`'s [`kind()` method][kind], which provides us
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with [`TyKind`][TyKind] of a `Ty`.
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## `TyKind`
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`TyKind` defines the kinds of types in Rust's type system.
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Peeking into [`TyKind` documentation][TyKind], we will see that it is an
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enum of 27 variants, including items such as `Bool`, `Int`, `Ref`, etc.
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enum of over 25 variants, including items such as `Bool`, `Int`, `Ref`, etc.
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### `kind` Usage
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The `TyKind` of `Ty` can be returned by calling [`Ty.kind` method][kind].
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The `TyKind` of `Ty` can be returned by calling [`Ty.kind()` method][kind].
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We often use this method to perform pattern matching in Clippy.
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For instance, if we want to check for a `struct`, we could examine if the
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@ -107,15 +107,21 @@ impl LateLintPass<'_> for MyStructLint {
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We've been talking about [`ty::Ty`][middle_ty] this whole time without addressing [`hir::Ty`][hir_ty], but the latter
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is also important to understand.
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`hir::Ty` would represent *what* an user wrote, while `ty::Ty` would understand the meaning of it (because it has more
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information).
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`hir::Ty` would represent *what* the user wrote, while `ty::Ty` is how the compiler sees the type and has more
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information. Example:
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**Example: `fn foo(x: u32) -> u32 { x }`**
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```rust
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fn foo(x: u32) -> u32 { x }
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```
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Here the HIR sees the types without "thinking" about them, it knows that the function takes an `u32` and returns
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an `u32`. But at the `ty::Ty` level the compiler understands that they're the same type, in-depth lifetimes, etc...
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an `u32`. As far as `hir::Ty` is concerned those might be different types. But at the `ty::Ty` level the compiler
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understands that they're the same type, in-depth lifetimes, etc...
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you can use the [`hir_ty_to_ty`][hir_ty_to_ty] function to convert from a `hir::Ty` to a `ty::Ty`
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To get from a `hir::Ty` to a `ty::Ty`, you can use the [`hir_ty_to_ty`][hir_ty_to_ty] function outside of bodies or
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outside of bodies the [`TypeckResults::node_type()`][node_type] method.
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> **Warning**: Don't use `hir_ty_to_ty` inside of bodies, because this can cause ICEs.
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## Useful Links
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@ -130,6 +136,7 @@ in this chapter:
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[Adt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/enum.TyKind.html#variant.Adt
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[AdtDef]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/adt/struct.AdtDef.html
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[expr_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckResults.html#method.expr_ty
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[node_type]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TypeckResults.html#method.node_type
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[is_char]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html#method.is_char
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[is_char_source]: https://doc.rust-lang.org/nightly/nightly-rustc/src/rustc_middle/ty/sty.rs.html#1831-1834
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[kind]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html#method.kind
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