67 lines
1.6 KiB
Go
67 lines
1.6 KiB
Go
package checkers
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import (
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"go/ast"
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"go/token"
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"github.com/go-lintpack/lintpack"
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"github.com/go-lintpack/lintpack/astwalk"
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"github.com/go-toolsmith/astcast"
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"github.com/go-toolsmith/astcopy"
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"github.com/go-toolsmith/astequal"
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"github.com/go-toolsmith/typep"
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)
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func init() {
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var info lintpack.CheckerInfo
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info.Name = "offBy1"
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info.Tags = []string{"diagnostic", "experimental"}
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info.Summary = "Detects various off-by-one kind of errors"
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info.Before = `xs[len(xs)]`
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info.After = `xs[len(xs)-1]`
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collection.AddChecker(&info, func(ctx *lintpack.CheckerContext) lintpack.FileWalker {
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return astwalk.WalkerForExpr(&offBy1Checker{ctx: ctx})
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})
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}
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type offBy1Checker struct {
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astwalk.WalkHandler
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ctx *lintpack.CheckerContext
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}
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func (c *offBy1Checker) VisitExpr(e ast.Expr) {
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// TODO(Quasilyte): handle more off-by-1 patterns.
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// TODO(Quasilyte): check whether go/analysis can help here.
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// Detect s[len(s)] expressions that always panic.
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// The correct form is s[len(s)-1].
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indexExpr := astcast.ToIndexExpr(e)
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indexed := indexExpr.X
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if !typep.IsSlice(c.ctx.TypesInfo.TypeOf(indexed)) {
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return
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}
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if !typep.SideEffectFree(c.ctx.TypesInfo, indexed) {
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return
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}
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call := astcast.ToCallExpr(indexExpr.Index)
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if astcast.ToIdent(call.Fun).Name != "len" {
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return
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}
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if len(call.Args) != 1 || !astequal.Expr(call.Args[0], indexed) {
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return
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}
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c.warnLenIndex(indexExpr)
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}
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func (c *offBy1Checker) warnLenIndex(cause *ast.IndexExpr) {
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suggest := astcopy.IndexExpr(cause)
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suggest.Index = &ast.BinaryExpr{
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Op: token.SUB,
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X: cause.Index,
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Y: &ast.BasicLit{Value: "1"},
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}
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c.ctx.Warn(cause, "index expr always panics; maybe you wanted %s?", suggest)
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}
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