src/tools/clippy/clippy_utils/src/higher.rs

   1 //! This module contains functions that retrieve specific elements.
   2
   3 #![deny(clippy::missing_docs_in_private_items)]
   4
   5 use crate::ty::is_type_diagnostic_item;
   6 use crate::{is_expn_of, last_path_segment, match_def_path, paths};
   7 use if_chain::if_chain;
   8 use rustc_ast::ast::{self, LitKind};
   9 use rustc_hir as hir;
  10 use rustc_hir::{
  11     Arm, Block, BorrowKind, Expr, ExprKind, HirId, LoopSource, MatchSource, Node, Pat, QPath, StmtKind, UnOp,
  12 };
  13 use rustc_lint::LateContext;
  14 use rustc_span::{sym, symbol, ExpnKind, Span, Symbol};
  15
  16 /// The essential nodes of a desugared for loop as well as the entire span:
  17 /// `for pat in arg { body }` becomes `(pat, arg, body)`. Return `(pat, arg, body, span)`.
  18 pub struct ForLoop<'tcx> {
  19     /// `for` loop item
  20     pub pat: &'tcx hir::Pat<'tcx>,
  21     /// `IntoIterator` argument
  22     pub arg: &'tcx hir::Expr<'tcx>,
  23     /// `for` loop body
  24     pub body: &'tcx hir::Expr<'tcx>,
  25     /// Compare this against `hir::Destination.target`
  26     pub loop_id: HirId,
  27     /// entire `for` loop span
  28     pub span: Span,
  29 }
  30
  31 impl<'tcx> ForLoop<'tcx> {
  32     /// Parses a desugared `for` loop
  33     pub fn hir(expr: &Expr<'tcx>) -> Option<Self> {
  34         if_chain! {
  35             if let hir::ExprKind::DropTemps(e) = expr.kind;
  36             if let hir::ExprKind::Match(iterexpr, [arm], hir::MatchSource::ForLoopDesugar) = e.kind;
  37             if let hir::ExprKind::Call(_, [arg]) = iterexpr.kind;
  38             if let hir::ExprKind::Loop(block, ..) = arm.body.kind;
  39             if let [stmt] = &*block.stmts;
  40             if let hir::StmtKind::Expr(e) = stmt.kind;
  41             if let hir::ExprKind::Match(_, [_, some_arm], _) = e.kind;
  42             if let hir::PatKind::Struct(_, [field], _) = some_arm.pat.kind;
  43             then {
  44                 return Some(Self {
  45                     pat: field.pat,
  46                     arg,
  47                     body: some_arm.body,
  48                     loop_id: arm.body.hir_id,
  49                     span: expr.span.ctxt().outer_expn_data().call_site,
  50                 });
  51             }
  52         }
  53         None
  54     }
  55 }
  56
  57 /// An `if` expression without `DropTemps`
  58 pub struct If<'hir> {
  59     /// `if` condition
  60     pub cond: &'hir Expr<'hir>,
  61     /// `if` then expression
  62     pub then: &'hir Expr<'hir>,
  63     /// `else` expression
  64     pub r#else: Option<&'hir Expr<'hir>>,
  65 }
  66
  67 impl<'hir> If<'hir> {
  68     #[inline]
  69     /// Parses an `if` expression
  70     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
  71         if let ExprKind::If(
  72             Expr {
  73                 kind: ExprKind::DropTemps(cond),
  74                 ..
  75             },
  76             then,
  77             r#else,
  78         ) = expr.kind
  79         {
  80             Some(Self { cond, then, r#else })
  81         } else {
  82             None
  83         }
  84     }
  85 }
  86
  87 /// An `if let` expression
  88 pub struct IfLet<'hir> {
  89     /// `if let` pattern
  90     pub let_pat: &'hir Pat<'hir>,
  91     /// `if let` scrutinee
  92     pub let_expr: &'hir Expr<'hir>,
  93     /// `if let` then expression
  94     pub if_then: &'hir Expr<'hir>,
  95     /// `if let` else expression
  96     pub if_else: Option<&'hir Expr<'hir>>,
  97 }
  98
  99 impl<'hir> IfLet<'hir> {
 100     /// Parses an `if let` expression
 101     pub fn hir(cx: &LateContext<'_>, expr: &Expr<'hir>) -> Option<Self> {
 102         if let ExprKind::If(
 103             Expr {
 104                 kind:
 105                     ExprKind::Let(hir::Let {
 106                         pat: let_pat,
 107                         init: let_expr,
 108                         ..
 109                     }),
 110                 ..
 111             },
 112             if_then,
 113             if_else,
 114         ) = expr.kind
 115         {
 116             let mut iter = cx.tcx.hir().parent_iter(expr.hir_id);
 117             if let Some((_, Node::Block(Block { stmts: [], .. }))) = iter.next() {
 118                 if let Some((
 119                     _,
 120                     Node::Expr(Expr {
 121                         kind: ExprKind::Loop(_, _, LoopSource::While, _),
 122                         ..
 123                     }),
 124                 )) = iter.next()
 125                 {
 126                     // while loop desugar
 127                     return None;
 128                 }
 129             }
 130             return Some(Self {
 131                 let_pat,
 132                 let_expr,
 133                 if_then,
 134                 if_else,
 135             });
 136         }
 137         None
 138     }
 139 }
 140
 141 /// An `if let` or `match` expression. Useful for lints that trigger on one or the other.
 142 pub enum IfLetOrMatch<'hir> {
 143     /// Any `match` expression
 144     Match(&'hir Expr<'hir>, &'hir [Arm<'hir>], MatchSource),
 145     /// scrutinee, pattern, then block, else block
 146     IfLet(
 147         &'hir Expr<'hir>,
 148         &'hir Pat<'hir>,
 149         &'hir Expr<'hir>,
 150         Option<&'hir Expr<'hir>>,
 151     ),
 152 }
 153
 154 impl<'hir> IfLetOrMatch<'hir> {
 155     /// Parses an `if let` or `match` expression
 156     pub fn parse(cx: &LateContext<'_>, expr: &Expr<'hir>) -> Option<Self> {
 157         match expr.kind {
 158             ExprKind::Match(expr, arms, source) => Some(Self::Match(expr, arms, source)),
 159             _ => IfLet::hir(cx, expr).map(
 160                 |IfLet {
 161                      let_expr,
 162                      let_pat,
 163                      if_then,
 164                      if_else,
 165                  }| { Self::IfLet(let_expr, let_pat, if_then, if_else) },
 166             ),
 167         }
 168     }
 169 }
 170
 171 /// An `if` or `if let` expression
 172 pub struct IfOrIfLet<'hir> {
 173     /// `if` condition that is maybe a `let` expression
 174     pub cond: &'hir Expr<'hir>,
 175     /// `if` then expression
 176     pub then: &'hir Expr<'hir>,
 177     /// `else` expression
 178     pub r#else: Option<&'hir Expr<'hir>>,
 179 }
 180
 181 impl<'hir> IfOrIfLet<'hir> {
 182     #[inline]
 183     /// Parses an `if` or `if let` expression
 184     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
 185         if let ExprKind::If(cond, then, r#else) = expr.kind {
 186             if let ExprKind::DropTemps(new_cond) = cond.kind {
 187                 return Some(Self {
 188                     cond: new_cond,
 189                     r#else,
 190                     then,
 191                 });
 192             }
 193             if let ExprKind::Let(..) = cond.kind {
 194                 return Some(Self { cond, then, r#else });
 195             }
 196         }
 197         None
 198     }
 199 }
 200
 201 /// Represent a range akin to `ast::ExprKind::Range`.
 202 #[derive(Debug, Copy, Clone)]
 203 pub struct Range<'a> {
 204     /// The lower bound of the range, or `None` for ranges such as `..X`.
 205     pub start: Option<&'a hir::Expr<'a>>,
 206     /// The upper bound of the range, or `None` for ranges such as `X..`.
 207     pub end: Option<&'a hir::Expr<'a>>,
 208     /// Whether the interval is open or closed.
 209     pub limits: ast::RangeLimits,
 210 }
 211
 212 impl<'a> Range<'a> {
 213     /// Higher a `hir` range to something similar to `ast::ExprKind::Range`.
 214     pub fn hir(expr: &'a hir::Expr<'_>) -> Option<Range<'a>> {
 215         /// Finds the field named `name` in the field. Always return `Some` for
 216         /// convenience.
 217         fn get_field<'c>(name: &str, fields: &'c [hir::ExprField<'_>]) -> Option<&'c hir::Expr<'c>> {
 218             let expr = &fields.iter().find(|field| field.ident.name.as_str() == name)?.expr;
 219             Some(expr)
 220         }
 221
 222         match expr.kind {
 223             hir::ExprKind::Call(path, args)
 224                 if matches!(
 225                     path.kind,
 226                     hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::RangeInclusiveNew, ..))
 227                 ) =>
 228             {
 229                 Some(Range {
 230                     start: Some(&args[0]),
 231                     end: Some(&args[1]),
 232                     limits: ast::RangeLimits::Closed,
 233                 })
 234             },
 235             hir::ExprKind::Struct(path, fields, None) => match &path {
 236                 hir::QPath::LangItem(hir::LangItem::RangeFull, ..) => Some(Range {
 237                     start: None,
 238                     end: None,
 239                     limits: ast::RangeLimits::HalfOpen,
 240                 }),
 241                 hir::QPath::LangItem(hir::LangItem::RangeFrom, ..) => Some(Range {
 242                     start: Some(get_field("start", fields)?),
 243                     end: None,
 244                     limits: ast::RangeLimits::HalfOpen,
 245                 }),
 246                 hir::QPath::LangItem(hir::LangItem::Range, ..) => Some(Range {
 247                     start: Some(get_field("start", fields)?),
 248                     end: Some(get_field("end", fields)?),
 249                     limits: ast::RangeLimits::HalfOpen,
 250                 }),
 251                 hir::QPath::LangItem(hir::LangItem::RangeToInclusive, ..) => Some(Range {
 252                     start: None,
 253                     end: Some(get_field("end", fields)?),
 254                     limits: ast::RangeLimits::Closed,
 255                 }),
 256                 hir::QPath::LangItem(hir::LangItem::RangeTo, ..) => Some(Range {
 257                     start: None,
 258                     end: Some(get_field("end", fields)?),
 259                     limits: ast::RangeLimits::HalfOpen,
 260                 }),
 261                 _ => None,
 262             },
 263             _ => None,
 264         }
 265     }
 266 }
 267
 268 /// Represent the pre-expansion arguments of a `vec!` invocation.
 269 pub enum VecArgs<'a> {
 270     /// `vec![elem; len]`
 271     Repeat(&'a hir::Expr<'a>, &'a hir::Expr<'a>),
 272     /// `vec![a, b, c]`
 273     Vec(&'a [hir::Expr<'a>]),
 274 }
 275
 276 impl<'a> VecArgs<'a> {
 277     /// Returns the arguments of the `vec!` macro if this expression was expanded
 278     /// from `vec!`.
 279     pub fn hir(cx: &LateContext<'_>, expr: &'a hir::Expr<'_>) -> Option<VecArgs<'a>> {
 280         if_chain! {
 281             if let hir::ExprKind::Call(fun, args) = expr.kind;
 282             if let hir::ExprKind::Path(ref qpath) = fun.kind;
 283             if is_expn_of(fun.span, "vec").is_some();
 284             if let Some(fun_def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
 285             then {
 286                 return if match_def_path(cx, fun_def_id, &paths::VEC_FROM_ELEM) && args.len() == 2 {
 287                     // `vec![elem; size]` case
 288                     Some(VecArgs::Repeat(&args[0], &args[1]))
 289                 }
 290                 else if match_def_path(cx, fun_def_id, &paths::SLICE_INTO_VEC) && args.len() == 1 {
 291                     // `vec![a, b, c]` case
 292                     if_chain! {
 293                         if let hir::ExprKind::Box(boxed) = args[0].kind;
 294                         if let hir::ExprKind::Array(args) = boxed.kind;
 295                         then {
 296                             return Some(VecArgs::Vec(args));
 297                         }
 298                     }
 299
 300                     None
 301                 }
 302                 else if match_def_path(cx, fun_def_id, &paths::VEC_NEW) && args.is_empty() {
 303                     Some(VecArgs::Vec(&[]))
 304                 }
 305                 else {
 306                     None
 307                 };
 308             }
 309         }
 310
 311         None
 312     }
 313 }
 314
 315 /// A desugared `while` loop
 316 pub struct While<'hir> {
 317     /// `while` loop condition
 318     pub condition: &'hir Expr<'hir>,
 319     /// `while` loop body
 320     pub body: &'hir Expr<'hir>,
 321 }
 322
 323 impl<'hir> While<'hir> {
 324     #[inline]
 325     /// Parses a desugared `while` loop
 326     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
 327         if let ExprKind::Loop(
 328             Block {
 329                 expr:
 330                     Some(Expr {
 331                         kind:
 332                             ExprKind::If(
 333                                 Expr {
 334                                     kind: ExprKind::DropTemps(condition),
 335                                     ..
 336                                 },
 337                                 body,
 338                                 _,
 339                             ),
 340                         ..
 341                     }),
 342                 ..
 343             },
 344             _,
 345             LoopSource::While,
 346             _,
 347         ) = expr.kind
 348         {
 349             return Some(Self { condition, body });
 350         }
 351         None
 352     }
 353 }
 354
 355 /// A desugared `while let` loop
 356 pub struct WhileLet<'hir> {
 357     /// `while let` loop item pattern
 358     pub let_pat: &'hir Pat<'hir>,
 359     /// `while let` loop scrutinee
 360     pub let_expr: &'hir Expr<'hir>,
 361     /// `while let` loop body
 362     pub if_then: &'hir Expr<'hir>,
 363 }
 364
 365 impl<'hir> WhileLet<'hir> {
 366     #[inline]
 367     /// Parses a desugared `while let` loop
 368     pub const fn hir(expr: &Expr<'hir>) -> Option<Self> {
 369         if let ExprKind::Loop(
 370             Block {
 371                 expr:
 372                     Some(Expr {
 373                         kind:
 374                             ExprKind::If(
 375                                 Expr {
 376                                     kind:
 377                                         ExprKind::Let(hir::Let {
 378                                             pat: let_pat,
 379                                             init: let_expr,
 380                                             ..
 381                                         }),
 382                                     ..
 383                                 },
 384                                 if_then,
 385                                 _,
 386                             ),
 387                         ..
 388                     }),
 389                 ..
 390             },
 391             _,
 392             LoopSource::While,
 393             _,
 394         ) = expr.kind
 395         {
 396             return Some(Self {
 397                 let_pat,
 398                 let_expr,
 399                 if_then,
 400             });
 401         }
 402         None
 403     }
 404 }
 405
 406 /// Converts a hir binary operator to the corresponding `ast` type.
 407 #[must_use]
 408 pub fn binop(op: hir::BinOpKind) -> ast::BinOpKind {
 409     match op {
 410         hir::BinOpKind::Eq => ast::BinOpKind::Eq,
 411         hir::BinOpKind::Ge => ast::BinOpKind::Ge,
 412         hir::BinOpKind::Gt => ast::BinOpKind::Gt,
 413         hir::BinOpKind::Le => ast::BinOpKind::Le,
 414         hir::BinOpKind::Lt => ast::BinOpKind::Lt,
 415         hir::BinOpKind::Ne => ast::BinOpKind::Ne,
 416         hir::BinOpKind::Or => ast::BinOpKind::Or,
 417         hir::BinOpKind::Add => ast::BinOpKind::Add,
 418         hir::BinOpKind::And => ast::BinOpKind::And,
 419         hir::BinOpKind::BitAnd => ast::BinOpKind::BitAnd,
 420         hir::BinOpKind::BitOr => ast::BinOpKind::BitOr,
 421         hir::BinOpKind::BitXor => ast::BinOpKind::BitXor,
 422         hir::BinOpKind::Div => ast::BinOpKind::Div,
 423         hir::BinOpKind::Mul => ast::BinOpKind::Mul,
 424         hir::BinOpKind::Rem => ast::BinOpKind::Rem,
 425         hir::BinOpKind::Shl => ast::BinOpKind::Shl,
 426         hir::BinOpKind::Shr => ast::BinOpKind::Shr,
 427         hir::BinOpKind::Sub => ast::BinOpKind::Sub,
 428     }
 429 }
 430
 431 /// Extract args from an assert-like macro.
 432 /// Currently working with:
 433 /// - `assert!`, `assert_eq!` and `assert_ne!`
 434 /// - `debug_assert!`, `debug_assert_eq!` and `debug_assert_ne!`
 435 /// For example:
 436 /// `assert!(expr)` will return `Some([expr])`
 437 /// `debug_assert_eq!(a, b)` will return `Some([a, b])`
 438 pub fn extract_assert_macro_args<'tcx>(e: &'tcx Expr<'tcx>) -> Option<Vec<&'tcx Expr<'tcx>>> {
 439     /// Try to match the AST for a pattern that contains a match, for example when two args are
 440     /// compared
 441     fn ast_matchblock(matchblock_expr: &'tcx Expr<'tcx>) -> Option<Vec<&Expr<'_>>> {
 442         if_chain! {
 443             if let ExprKind::Match(headerexpr, _, _) = &matchblock_expr.kind;
 444             if let ExprKind::Tup([lhs, rhs]) = &headerexpr.kind;
 445             if let ExprKind::AddrOf(BorrowKind::Ref, _, lhs) = lhs.kind;
 446             if let ExprKind::AddrOf(BorrowKind::Ref, _, rhs) = rhs.kind;
 447             then {
 448                 return Some(vec![lhs, rhs]);
 449             }
 450         }
 451         None
 452     }
 453
 454     if let ExprKind::Block(block, _) = e.kind {
 455         if block.stmts.len() == 1 {
 456             if let StmtKind::Semi(matchexpr) = block.stmts.get(0)?.kind {
 457                 // macros with unique arg: `{debug_}assert!` (e.g., `debug_assert!(some_condition)`)
 458                 if_chain! {
 459                     if let Some(If { cond, .. }) = If::hir(matchexpr);
 460                     if let ExprKind::Unary(UnOp::Not, condition) = cond.kind;
 461                     then {
 462                         return Some(vec![condition]);
 463                     }
 464                 }
 465
 466                 // debug macros with two args: `debug_assert_{ne, eq}` (e.g., `assert_ne!(a, b)`)
 467                 if_chain! {
 468                     if let ExprKind::Block(matchblock,_) = matchexpr.kind;
 469                     if let Some(matchblock_expr) = matchblock.expr;
 470                     then {
 471                         return ast_matchblock(matchblock_expr);
 472                     }
 473                 }
 474             }
 475         } else if let Some(matchblock_expr) = block.expr {
 476             // macros with two args: `assert_{ne, eq}` (e.g., `assert_ne!(a, b)`)
 477             return ast_matchblock(matchblock_expr);
 478         }
 479     }
 480     None
 481 }
 482
 483 /// A parsed `format!` expansion
 484 pub struct FormatExpn<'tcx> {
 485     /// Span of `format!(..)`
 486     pub call_site: Span,
 487     /// Inner `format_args!` expansion
 488     pub format_args: FormatArgsExpn<'tcx>,
 489 }
 490
 491 impl FormatExpn<'tcx> {
 492     /// Parses an expanded `format!` invocation
 493     pub fn parse(expr: &'tcx Expr<'tcx>) -> Option<Self> {
 494         if_chain! {
 495             if let ExprKind::Block(block, _) = expr.kind;
 496             if let [stmt] = block.stmts;
 497             if let StmtKind::Local(local) = stmt.kind;
 498             if let Some(init) = local.init;
 499             if let ExprKind::Call(_, [format_args]) = init.kind;
 500             let expn_data = expr.span.ctxt().outer_expn_data();
 501             if let ExpnKind::Macro(_, sym::format) = expn_data.kind;
 502             if let Some(format_args) = FormatArgsExpn::parse(format_args);
 503             then {
 504                 Some(FormatExpn {
 505                     call_site: expn_data.call_site,
 506                     format_args,
 507                 })
 508             } else {
 509                 None
 510             }
 511         }
 512     }
 513 }
 514
 515 /// A parsed `format_args!` expansion
 516 pub struct FormatArgsExpn<'tcx> {
 517     /// Span of the first argument, the format string
 518     pub format_string_span: Span,
 519     /// Values passed after the format string
 520     pub value_args: Vec<&'tcx Expr<'tcx>>,
 521
 522     /// String literal expressions which represent the format string split by "{}"
 523     pub format_string_parts: &'tcx [Expr<'tcx>],
 524     /// Symbols corresponding to [`Self::format_string_parts`]
 525     pub format_string_symbols: Vec<Symbol>,
 526     /// Expressions like `ArgumentV1::new(arg0, Debug::fmt)`
 527     pub args: &'tcx [Expr<'tcx>],
 528     /// The final argument passed to `Arguments::new_v1_formatted`, if applicable
 529     pub fmt_expr: Option<&'tcx Expr<'tcx>>,
 530 }
 531
 532 impl FormatArgsExpn<'tcx> {
 533     /// Parses an expanded `format_args!` or `format_args_nl!` invocation
 534     pub fn parse(expr: &'tcx Expr<'tcx>) -> Option<Self> {
 535         if_chain! {
 536             if let ExpnKind::Macro(_, name) = expr.span.ctxt().outer_expn_data().kind;
 537             let name = name.as_str();
 538             if name.ends_with("format_args") || name.ends_with("format_args_nl");
 539             if let ExprKind::Call(_, args) = expr.kind;
 540             if let Some((strs_ref, args, fmt_expr)) = match args {
 541                 // Arguments::new_v1
 542                 [strs_ref, args] => Some((strs_ref, args, None)),
 543                 // Arguments::new_v1_formatted
 544                 [strs_ref, args, fmt_expr, _unsafe_arg] => Some((strs_ref, args, Some(fmt_expr))),
 545                 _ => None,
 546             };
 547             if let ExprKind::AddrOf(BorrowKind::Ref, _, strs_arr) = strs_ref.kind;
 548             if let ExprKind::Array(format_string_parts) = strs_arr.kind;
 549             if let Some(format_string_symbols) = format_string_parts
 550                 .iter()
 551                 .map(|e| {
 552                     if let ExprKind::Lit(lit) = &e.kind {
 553                         if let LitKind::Str(symbol, _style) = lit.node {
 554                             return Some(symbol);
 555                         }
 556                     }
 557                     None
 558                 })
 559                 .collect();
 560             if let ExprKind::AddrOf(BorrowKind::Ref, _, args) = args.kind;
 561             if let ExprKind::Match(args, [arm], _) = args.kind;
 562             if let ExprKind::Tup(value_args) = args.kind;
 563             if let Some(value_args) = value_args
 564                 .iter()
 565                 .map(|e| match e.kind {
 566                     ExprKind::AddrOf(_, _, e) => Some(e),
 567                     _ => None,
 568                 })
 569                 .collect();
 570             if let ExprKind::Array(args) = arm.body.kind;
 571             then {
 572                 Some(FormatArgsExpn {
 573                     format_string_span: strs_ref.span,
 574                     value_args,
 575                     format_string_parts,
 576                     format_string_symbols,
 577                     args,
 578                     fmt_expr,
 579                 })
 580             } else {
 581                 None
 582             }
 583         }
 584     }
 585
 586     /// Returns a vector of `FormatArgsArg`.
 587     pub fn args(&self) -> Option<Vec<FormatArgsArg<'tcx>>> {
 588         if let Some(expr) = self.fmt_expr {
 589             if_chain! {
 590                 if let ExprKind::AddrOf(BorrowKind::Ref, _, expr) = expr.kind;
 591                 if let ExprKind::Array(exprs) = expr.kind;
 592                 then {
 593                     exprs.iter().map(|fmt| {
 594                         if_chain! {
 595                             // struct `core::fmt::rt::v1::Argument`
 596                             if let ExprKind::Struct(_, fields, _) = fmt.kind;
 597                             if let Some(position_field) = fields.iter().find(|f| f.ident.name == sym::position);
 598                             if let ExprKind::Lit(lit) = &position_field.expr.kind;
 599                             if let LitKind::Int(position, _) = lit.node;
 600                             if let Ok(i) = usize::try_from(position);
 601                             let arg = &self.args[i];
 602                             if let ExprKind::Call(_, [arg_name, _]) = arg.kind;
 603                             if let ExprKind::Field(_, j) = arg_name.kind;
 604                             if let Ok(j) = j.name.as_str().parse::<usize>();
 605                             then {
 606                                 Some(FormatArgsArg { value: self.value_args[j], arg, fmt: Some(fmt) })
 607                             } else {
 608                                 None
 609                             }
 610                         }
 611                     }).collect()
 612                 } else {
 613                     None
 614                 }
 615             }
 616         } else {
 617             Some(
 618                 self.value_args
 619                     .iter()
 620                     .zip(self.args.iter())
 621                     .map(|(value, arg)| FormatArgsArg { value, arg, fmt: None })
 622                     .collect(),
 623             )
 624         }
 625     }
 626 }
 627
 628 /// Type representing a `FormatArgsExpn`'s format arguments
 629 pub struct FormatArgsArg<'tcx> {
 630     /// An element of `value_args` according to `position`
 631     pub value: &'tcx Expr<'tcx>,
 632     /// An element of `args` according to `position`
 633     pub arg: &'tcx Expr<'tcx>,
 634     /// An element of `fmt_expn`
 635     pub fmt: Option<&'tcx Expr<'tcx>>,
 636 }
 637
 638 impl<'tcx> FormatArgsArg<'tcx> {
 639     /// Returns true if any formatting parameters are used that would have an effect on strings,
 640     /// like `{:+2}` instead of just `{}`.
 641     pub fn has_string_formatting(&self) -> bool {
 642         self.fmt.map_or(false, |fmt| {
 643             // `!` because these conditions check that `self` is unformatted.
 644             !if_chain! {
 645                 // struct `core::fmt::rt::v1::Argument`
 646                 if let ExprKind::Struct(_, fields, _) = fmt.kind;
 647                 if let Some(format_field) = fields.iter().find(|f| f.ident.name == sym::format);
 648                 // struct `core::fmt::rt::v1::FormatSpec`
 649                 if let ExprKind::Struct(_, subfields, _) = format_field.expr.kind;
 650                 let mut precision_found = false;
 651                 let mut width_found = false;
 652                 if subfields.iter().all(|field| {
 653                     match field.ident.name {
 654                         sym::precision => {
 655                             precision_found = true;
 656                             if let ExprKind::Path(ref precision_path) = field.expr.kind {
 657                                 last_path_segment(precision_path).ident.name == sym::Implied
 658                             } else {
 659                                 false
 660                             }
 661                         }
 662                         sym::width => {
 663                             width_found = true;
 664                             if let ExprKind::Path(ref width_qpath) = field.expr.kind {
 665                                 last_path_segment(width_qpath).ident.name == sym::Implied
 666                             } else {
 667                                 false
 668                             }
 669                         }
 670                         _ => true,
 671                     }
 672                 });
 673                 if precision_found && width_found;
 674                 then { true } else { false }
 675             }
 676         })
 677     }
 678
 679     /// Returns true if the argument is formatted using `Display::fmt`.
 680     pub fn is_display(&self) -> bool {
 681         if_chain! {
 682             if let ExprKind::Call(_, [_, format_field]) = self.arg.kind;
 683             if let ExprKind::Path(QPath::Resolved(_, path)) = format_field.kind;
 684             if let [.., t, _] = path.segments;
 685             if t.ident.name == sym::Display;
 686             then { true } else { false }
 687         }
 688     }
 689 }
 690
 691 /// A parsed `panic!` expansion
 692 pub struct PanicExpn<'tcx> {
 693     /// Span of `panic!(..)`
 694     pub call_site: Span,
 695     /// Inner `format_args!` expansion
 696     pub format_args: FormatArgsExpn<'tcx>,
 697 }
 698
 699 impl PanicExpn<'tcx> {
 700     /// Parses an expanded `panic!` invocation
 701     pub fn parse(expr: &'tcx Expr<'tcx>) -> Option<Self> {
 702         if_chain! {
 703             if let ExprKind::Call(_, [format_args]) = expr.kind;
 704             let expn_data = expr.span.ctxt().outer_expn_data();
 705             if let Some(format_args) = FormatArgsExpn::parse(format_args);
 706             then {
 707                 Some(PanicExpn {
 708                     call_site: expn_data.call_site,
 709                     format_args,
 710                 })
 711             } else {
 712                 None
 713             }
 714         }
 715     }
 716 }
 717
 718 /// A parsed `Vec` initialization expression
 719 #[derive(Clone, Copy)]
 720 pub enum VecInitKind {
 721     /// `Vec::new()`
 722     New,
 723     /// `Vec::default()` or `Default::default()`
 724     Default,
 725     /// `Vec::with_capacity(123)`
 726     WithLiteralCapacity(u64),
 727     /// `Vec::with_capacity(slice.len())`
 728     WithExprCapacity(HirId),
 729 }
 730
 731 /// Checks if given expression is an initialization of `Vec` and returns its kind.
 732 pub fn get_vec_init_kind<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Option<VecInitKind> {
 733     if let ExprKind::Call(func, args) = expr.kind {
 734         match func.kind {
 735             ExprKind::Path(QPath::TypeRelative(ty, name))
 736                 if is_type_diagnostic_item(cx, cx.typeck_results().node_type(ty.hir_id), sym::Vec) =>
 737             {
 738                 if name.ident.name == sym::new {
 739                     return Some(VecInitKind::New);
 740                 } else if name.ident.name == symbol::kw::Default {
 741                     return Some(VecInitKind::Default);
 742                 } else if name.ident.name.as_str() == "with_capacity" {
 743                     let arg = args.get(0)?;
 744                     if_chain! {
 745                         if let ExprKind::Lit(lit) = &arg.kind;
 746                         if let LitKind::Int(num, _) = lit.node;
 747                         then {
 748                             return Some(VecInitKind::WithLiteralCapacity(num.try_into().ok()?))
 749                         }
 750                     }
 751                     return Some(VecInitKind::WithExprCapacity(arg.hir_id));
 752                 }
 753             },
 754             ExprKind::Path(QPath::Resolved(_, path))
 755                 if match_def_path(cx, path.res.opt_def_id()?, &paths::DEFAULT_TRAIT_METHOD)
 756                     && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym::Vec) =>
 757             {
 758                 return Some(VecInitKind::Default);
 759             },
 760             _ => (),
 761         }
 762     }
 763     None
 764 }