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option-if-let-else - factor out some common code in eager_or_lazy.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,105 @@ | ||
| //! Utilities for evaluating whether eagerly evaluated expressions can be made lazy and vice versa. | ||
| //! | ||
| //! Things to consider: | ||
| //! - has the expression side-effects? | ||
| //! - is the expression computationally expensive? | ||
| //! | ||
| //! See lints: | ||
| //! - unnecessary-lazy-evaluations | ||
| //! - or-fun-call | ||
| //! - option-if-let-else | ||
| use crate::utils::is_ctor_or_promotable_const_function; | ||
| use rustc_hir::def::{DefKind, Res}; | ||
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|
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| use rustc_hir::intravisit; | ||
| use rustc_hir::intravisit::{NestedVisitorMap, Visitor}; | ||
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| use rustc_hir::{Block, Expr, ExprKind, Path, QPath}; | ||
| use rustc_lint::LateContext; | ||
| use rustc_middle::hir::map::Map; | ||
|
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||
| /// Is the expr pure (is it free from side-effects)? | ||
| /// This function is named so to stress that it isn't exhaustive and returns FNs. | ||
| fn identify_some_pure_patterns(expr: &Expr<'_>) -> bool { | ||
| match expr.kind { | ||
| ExprKind::Lit(..) | ExprKind::Path(..) | ExprKind::Field(..) => true, | ||
| ExprKind::AddrOf(_, _, addr_of_expr) => identify_some_pure_patterns(addr_of_expr), | ||
| ExprKind::Tup(tup_exprs) => tup_exprs.iter().all(|expr| identify_some_pure_patterns(expr)), | ||
| ExprKind::Struct(_, fields, expr) => { | ||
| fields.iter().all(|f| identify_some_pure_patterns(f.expr)) | ||
| && expr.map_or(true, |e| identify_some_pure_patterns(e)) | ||
| }, | ||
| ExprKind::Call( | ||
| &Expr { | ||
| kind: | ||
| ExprKind::Path(QPath::Resolved( | ||
| _, | ||
| Path { | ||
| res: Res::Def(DefKind::Ctor(..) | DefKind::Variant, ..), | ||
| .. | ||
| }, | ||
| )), | ||
| .. | ||
| }, | ||
| args, | ||
| ) => args.iter().all(|expr| identify_some_pure_patterns(expr)), | ||
| ExprKind::Block( | ||
| &Block { | ||
| stmts, | ||
| expr: Some(expr), | ||
| .. | ||
| }, | ||
| _, | ||
| ) => stmts.is_empty() && identify_some_pure_patterns(expr), | ||
| _ => false, | ||
| } | ||
| } | ||
|
|
||
| /// Identify some potentially computationally expensive patterns. | ||
| /// This function is named so to stress that its implementation is non-exhaustive. | ||
| /// It returns FNs and FPs. | ||
| fn identify_some_potentially_expensive_patterns<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { | ||
| // Searches an expression for method calls or function calls that aren't ctors | ||
| struct FunCallFinder<'a, 'tcx> { | ||
| cx: &'a LateContext<'tcx>, | ||
| found: bool, | ||
| } | ||
|
|
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| impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> { | ||
| type Map = Map<'tcx>; | ||
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| fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) { | ||
| let call_found = match &expr.kind { | ||
| // ignore enum and struct constructors | ||
| ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr), | ||
| ExprKind::MethodCall(..) => true, | ||
| _ => false, | ||
| }; | ||
|
|
||
| if call_found { | ||
| self.found |= true; | ||
| } | ||
|
|
||
| if !self.found { | ||
| intravisit::walk_expr(self, expr); | ||
| } | ||
| } | ||
|
|
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| fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { | ||
| NestedVisitorMap::None | ||
| } | ||
| } | ||
|
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| let mut finder = FunCallFinder { cx, found: false }; | ||
| finder.visit_expr(expr); | ||
| finder.found | ||
| } | ||
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| pub fn is_eagerness_candidate<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { | ||
| !identify_some_potentially_expensive_patterns(cx, expr) && identify_some_pure_patterns(expr) | ||
| } | ||
|
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||
| pub fn is_lazyness_candidate<'a, 'tcx>(cx: &'a LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool { | ||
| identify_some_potentially_expensive_patterns(cx, expr) | ||
| } |
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