Giant blob of minor changes

[dotfiles/.git] / .config / coc / extensions / coc-go-data / tools / pkg / mod / github.com / google / go-cmp@v0.5.1 / cmp / compare.go

// Copyright 2017, The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE.md file.

// Package cmp determines equality of values.
//
// This package is intended to be a more powerful and safer alternative to
// reflect.DeepEqual for comparing whether two values are semantically equal.
// It is intended to only be used in tests, as performance is not a goal and
// it may panic if it cannot compare the values. Its propensity towards
// panicking means that its unsuitable for production environments where a
// spurious panic may be fatal.
//
// The primary features of cmp are:
//
// • When the default behavior of equality does not suit the needs of the test,
// custom equality functions can override the equality operation.
// For example, an equality function may report floats as equal so long as they
// are within some tolerance of each other.
//
// • Types that have an Equal method may use that method to determine equality.
// This allows package authors to determine the equality operation for the types
// that they define.
//
// • If no custom equality functions are used and no Equal method is defined,
// equality is determined by recursively comparing the primitive kinds on both
// values, much like reflect.DeepEqual. Unlike reflect.DeepEqual, unexported
// fields are not compared by default; they result in panics unless suppressed
// by using an Ignore option (see cmpopts.IgnoreUnexported) or explicitly
// compared using the Exporter option.
package cmp

import (
        "fmt"
        "reflect"
        "strings"

        "github.com/google/go-cmp/cmp/internal/diff"
        "github.com/google/go-cmp/cmp/internal/flags"
        "github.com/google/go-cmp/cmp/internal/function"
        "github.com/google/go-cmp/cmp/internal/value"
)

// Equal reports whether x and y are equal by recursively applying the
// following rules in the given order to x and y and all of their sub-values:
//
// • Let S be the set of all Ignore, Transformer, and Comparer options that
// remain after applying all path filters, value filters, and type filters.
// If at least one Ignore exists in S, then the comparison is ignored.
// If the number of Transformer and Comparer options in S is greater than one,
// then Equal panics because it is ambiguous which option to use.
// If S contains a single Transformer, then use that to transform the current
// values and recursively call Equal on the output values.
// If S contains a single Comparer, then use that to compare the current values.
// Otherwise, evaluation proceeds to the next rule.
//
// • If the values have an Equal method of the form "(T) Equal(T) bool" or
// "(T) Equal(I) bool" where T is assignable to I, then use the result of
// x.Equal(y) even if x or y is nil. Otherwise, no such method exists and
// evaluation proceeds to the next rule.
//
// • Lastly, try to compare x and y based on their basic kinds.
// Simple kinds like booleans, integers, floats, complex numbers, strings, and
// channels are compared using the equivalent of the == operator in Go.
// Functions are only equal if they are both nil, otherwise they are unequal.
//
// Structs are equal if recursively calling Equal on all fields report equal.
// If a struct contains unexported fields, Equal panics unless an Ignore option
// (e.g., cmpopts.IgnoreUnexported) ignores that field or the Exporter option
// explicitly permits comparing the unexported field.
//
// Slices are equal if they are both nil or both non-nil, where recursively
// calling Equal on all non-ignored slice or array elements report equal.
// Empty non-nil slices and nil slices are not equal; to equate empty slices,
// consider using cmpopts.EquateEmpty.
//
// Maps are equal if they are both nil or both non-nil, where recursively
// calling Equal on all non-ignored map entries report equal.
// Map keys are equal according to the == operator.
// To use custom comparisons for map keys, consider using cmpopts.SortMaps.
// Empty non-nil maps and nil maps are not equal; to equate empty maps,
// consider using cmpopts.EquateEmpty.
//
// Pointers and interfaces are equal if they are both nil or both non-nil,
// where they have the same underlying concrete type and recursively
// calling Equal on the underlying values reports equal.
//
// Before recursing into a pointer, slice element, or map, the current path
// is checked to detect whether the address has already been visited.
// If there is a cycle, then the pointed at values are considered equal
// only if both addresses were previously visited in the same path step.
func Equal(x, y interface{}, opts ...Option) bool {
        s := newState(opts)
        s.compareAny(rootStep(x, y))
        return s.result.Equal()
}

// Diff returns a human-readable report of the differences between two values.
// It returns an empty string if and only if Equal returns true for the same
// input values and options.
//
// The output is displayed as a literal in pseudo-Go syntax.
// At the start of each line, a "-" prefix indicates an element removed from x,
// a "+" prefix to indicates an element added to y, and the lack of a prefix
// indicates an element common to both x and y. If possible, the output
// uses fmt.Stringer.String or error.Error methods to produce more humanly
// readable outputs. In such cases, the string is prefixed with either an
// 's' or 'e' character, respectively, to indicate that the method was called.
//
// Do not depend on this output being stable. If you need the ability to
// programmatically interpret the difference, consider using a custom Reporter.
func Diff(x, y interface{}, opts ...Option) string {
        s := newState(opts)

        // Optimization: If there are no other reporters, we can optimize for the
        // common case where the result is equal (and thus no reported difference).
        // This avoids the expensive construction of a difference tree.
        if len(s.reporters) == 0 {
                s.compareAny(rootStep(x, y))
                if s.result.Equal() {
                        return ""
                }
                s.result = diff.Result{} // Reset results
        }

        r := new(defaultReporter)
        s.reporters = append(s.reporters, reporter{r})
        s.compareAny(rootStep(x, y))
        d := r.String()
        if (d == "") != s.result.Equal() {
                panic("inconsistent difference and equality results")
        }
        return d
}

// rootStep constructs the first path step. If x and y have differing types,
// then they are stored within an empty interface type.
func rootStep(x, y interface{}) PathStep {
        vx := reflect.ValueOf(x)
        vy := reflect.ValueOf(y)

        // If the inputs are different types, auto-wrap them in an empty interface
        // so that they have the same parent type.
        var t reflect.Type
        if !vx.IsValid() || !vy.IsValid() || vx.Type() != vy.Type() {
                t = reflect.TypeOf((*interface{})(nil)).Elem()
                if vx.IsValid() {
                        vvx := reflect.New(t).Elem()
                        vvx.Set(vx)
                        vx = vvx
                }
                if vy.IsValid() {
                        vvy := reflect.New(t).Elem()
                        vvy.Set(vy)
                        vy = vvy
                }
        } else {
                t = vx.Type()
        }

        return &pathStep{t, vx, vy}
}

type state struct {
        // These fields represent the "comparison state".
        // Calling statelessCompare must not result in observable changes to these.
        result    diff.Result // The current result of comparison
        curPath   Path        // The current path in the value tree
        curPtrs   pointerPath // The current set of visited pointers
        reporters []reporter  // Optional reporters

        // recChecker checks for infinite cycles applying the same set of
        // transformers upon the output of itself.
        recChecker recChecker

        // dynChecker triggers pseudo-random checks for option correctness.
        // It is safe for statelessCompare to mutate this value.
        dynChecker dynChecker

        // These fields, once set by processOption, will not change.
        exporters []exporter // List of exporters for structs with unexported fields
        opts      Options    // List of all fundamental and filter options
}

func newState(opts []Option) *state {
        // Always ensure a validator option exists to validate the inputs.
        s := &state{opts: Options{validator{}}}
        s.curPtrs.Init()
        s.processOption(Options(opts))
        return s
}

func (s *state) processOption(opt Option) {
        switch opt := opt.(type) {
        case nil:
        case Options:
                for _, o := range opt {
                        s.processOption(o)
                }
        case coreOption:
                type filtered interface {
                        isFiltered() bool
                }
                if fopt, ok := opt.(filtered); ok && !fopt.isFiltered() {
                        panic(fmt.Sprintf("cannot use an unfiltered option: %v", opt))
                }
                s.opts = append(s.opts, opt)
        case exporter:
                s.exporters = append(s.exporters, opt)
        case reporter:
                s.reporters = append(s.reporters, opt)
        default:
                panic(fmt.Sprintf("unknown option %T", opt))
        }
}

// statelessCompare compares two values and returns the result.
// This function is stateless in that it does not alter the current result,
// or output to any registered reporters.
func (s *state) statelessCompare(step PathStep) diff.Result {
        // We do not save and restore curPath and curPtrs because all of the
        // compareX methods should properly push and pop from them.
        // It is an implementation bug if the contents of the paths differ from
        // when calling this function to when returning from it.

        oldResult, oldReporters := s.result, s.reporters
        s.result = diff.Result{} // Reset result
        s.reporters = nil        // Remove reporters to avoid spurious printouts
        s.compareAny(step)
        res := s.result
        s.result, s.reporters = oldResult, oldReporters
        return res
}

func (s *state) compareAny(step PathStep) {
        // Update the path stack.
        s.curPath.push(step)
        defer s.curPath.pop()
        for _, r := range s.reporters {
                r.PushStep(step)
                defer r.PopStep()
        }
        s.recChecker.Check(s.curPath)

        // Cycle-detection for slice elements (see NOTE in compareSlice).
        t := step.Type()
        vx, vy := step.Values()
        if si, ok := step.(SliceIndex); ok && si.isSlice && vx.IsValid() && vy.IsValid() {
                px, py := vx.Addr(), vy.Addr()
                if eq, visited := s.curPtrs.Push(px, py); visited {
                        s.report(eq, reportByCycle)
                        return
                }
                defer s.curPtrs.Pop(px, py)
        }

        // Rule 1: Check whether an option applies on this node in the value tree.
        if s.tryOptions(t, vx, vy) {
                return
        }

        // Rule 2: Check whether the type has a valid Equal method.
        if s.tryMethod(t, vx, vy) {
                return
        }

        // Rule 3: Compare based on the underlying kind.
        switch t.Kind() {
        case reflect.Bool:
                s.report(vx.Bool() == vy.Bool(), 0)
        case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
                s.report(vx.Int() == vy.Int(), 0)
        case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
                s.report(vx.Uint() == vy.Uint(), 0)
        case reflect.Float32, reflect.Float64:
                s.report(vx.Float() == vy.Float(), 0)
        case reflect.Complex64, reflect.Complex128:
                s.report(vx.Complex() == vy.Complex(), 0)
        case reflect.String:
                s.report(vx.String() == vy.String(), 0)
        case reflect.Chan, reflect.UnsafePointer:
                s.report(vx.Pointer() == vy.Pointer(), 0)
        case reflect.Func:
                s.report(vx.IsNil() && vy.IsNil(), 0)
        case reflect.Struct:
                s.compareStruct(t, vx, vy)
        case reflect.Slice, reflect.Array:
                s.compareSlice(t, vx, vy)
        case reflect.Map:
                s.compareMap(t, vx, vy)
        case reflect.Ptr:
                s.comparePtr(t, vx, vy)
        case reflect.Interface:
                s.compareInterface(t, vx, vy)
        default:
                panic(fmt.Sprintf("%v kind not handled", t.Kind()))
        }
}

func (s *state) tryOptions(t reflect.Type, vx, vy reflect.Value) bool {
        // Evaluate all filters and apply the remaining options.
        if opt := s.opts.filter(s, t, vx, vy); opt != nil {
                opt.apply(s, vx, vy)
                return true
        }
        return false
}

func (s *state) tryMethod(t reflect.Type, vx, vy reflect.Value) bool {
        // Check if this type even has an Equal method.
        m, ok := t.MethodByName("Equal")
        if !ok || !function.IsType(m.Type, function.EqualAssignable) {
                return false
        }

        eq := s.callTTBFunc(m.Func, vx, vy)
        s.report(eq, reportByMethod)
        return true
}

func (s *state) callTRFunc(f, v reflect.Value, step Transform) reflect.Value {
        v = sanitizeValue(v, f.Type().In(0))
        if !s.dynChecker.Next() {
                return f.Call([]reflect.Value{v})[0]
        }

        // Run the function twice and ensure that we get the same results back.
        // We run in goroutines so that the race detector (if enabled) can detect
        // unsafe mutations to the input.
        c := make(chan reflect.Value)
        go detectRaces(c, f, v)
        got := <-c
        want := f.Call([]reflect.Value{v})[0]
        if step.vx, step.vy = got, want; !s.statelessCompare(step).Equal() {
                // To avoid false-positives with non-reflexive equality operations,
                // we sanity check whether a value is equal to itself.
                if step.vx, step.vy = want, want; !s.statelessCompare(step).Equal() {
                        return want
                }
                panic(fmt.Sprintf("non-deterministic function detected: %s", function.NameOf(f)))
        }
        return want
}

func (s *state) callTTBFunc(f, x, y reflect.Value) bool {
        x = sanitizeValue(x, f.Type().In(0))
        y = sanitizeValue(y, f.Type().In(1))
        if !s.dynChecker.Next() {
                return f.Call([]reflect.Value{x, y})[0].Bool()
        }

        // Swapping the input arguments is sufficient to check that
        // f is symmetric and deterministic.
        // We run in goroutines so that the race detector (if enabled) can detect
        // unsafe mutations to the input.
        c := make(chan reflect.Value)
        go detectRaces(c, f, y, x)
        got := <-c
        want := f.Call([]reflect.Value{x, y})[0].Bool()
        if !got.IsValid() || got.Bool() != want {
                panic(fmt.Sprintf("non-deterministic or non-symmetric function detected: %s", function.NameOf(f)))
        }
        return want
}

func detectRaces(c chan<- reflect.Value, f reflect.Value, vs ...reflect.Value) {
        var ret reflect.Value
        defer func() {
                recover() // Ignore panics, let the other call to f panic instead
                c <- ret
        }()
        ret = f.Call(vs)[0]
}

// sanitizeValue converts nil interfaces of type T to those of type R,
// assuming that T is assignable to R.
// Otherwise, it returns the input value as is.
func sanitizeValue(v reflect.Value, t reflect.Type) reflect.Value {
        // TODO(≥go1.10): Workaround for reflect bug (https://golang.org/issue/22143).
        if !flags.AtLeastGo110 {
                if v.Kind() == reflect.Interface && v.IsNil() && v.Type() != t {
                        return reflect.New(t).Elem()
                }
        }
        return v
}

func (s *state) compareStruct(t reflect.Type, vx, vy reflect.Value) {
        var addr bool
        var vax, vay reflect.Value // Addressable versions of vx and vy

        var mayForce, mayForceInit bool
        step := StructField{&structField{}}
        for i := 0; i < t.NumField(); i++ {
                step.typ = t.Field(i).Type
                step.vx = vx.Field(i)
                step.vy = vy.Field(i)
                step.name = t.Field(i).Name
                step.idx = i
                step.unexported = !isExported(step.name)
                if step.unexported {
                        if step.name == "_" {
                                continue
                        }
                        // Defer checking of unexported fields until later to give an
                        // Ignore a chance to ignore the field.
                        if !vax.IsValid() || !vay.IsValid() {
                                // For retrieveUnexportedField to work, the parent struct must
                                // be addressable. Create a new copy of the values if
                                // necessary to make them addressable.
                                addr = vx.CanAddr() || vy.CanAddr()
                                vax = makeAddressable(vx)
                                vay = makeAddressable(vy)
                        }
                        if !mayForceInit {
                                for _, xf := range s.exporters {
                                        mayForce = mayForce || xf(t)
                                }
                                mayForceInit = true
                        }
                        step.mayForce = mayForce
                        step.paddr = addr
                        step.pvx = vax
                        step.pvy = vay
                        step.field = t.Field(i)
                }
                s.compareAny(step)
        }
}

func (s *state) compareSlice(t reflect.Type, vx, vy reflect.Value) {
        isSlice := t.Kind() == reflect.Slice
        if isSlice && (vx.IsNil() || vy.IsNil()) {
                s.report(vx.IsNil() && vy.IsNil(), 0)
                return
        }

        // NOTE: It is incorrect to call curPtrs.Push on the slice header pointer
        // since slices represents a list of pointers, rather than a single pointer.
        // The pointer checking logic must be handled on a per-element basis
        // in compareAny.
        //
        // A slice header (see reflect.SliceHeader) in Go is a tuple of a starting
        // pointer P, a length N, and a capacity C. Supposing each slice element has
        // a memory size of M, then the slice is equivalent to the list of pointers:
        //      [P+i*M for i in range(N)]
        //
        // For example, v[:0] and v[:1] are slices with the same starting pointer,
        // but they are clearly different values. Using the slice pointer alone
        // violates the assumption that equal pointers implies equal values.

        step := SliceIndex{&sliceIndex{pathStep: pathStep{typ: t.Elem()}, isSlice: isSlice}}
        withIndexes := func(ix, iy int) SliceIndex {
                if ix >= 0 {
                        step.vx, step.xkey = vx.Index(ix), ix
                } else {
                        step.vx, step.xkey = reflect.Value{}, -1
                }
                if iy >= 0 {
                        step.vy, step.ykey = vy.Index(iy), iy
                } else {
                        step.vy, step.ykey = reflect.Value{}, -1
                }
                return step
        }

        // Ignore options are able to ignore missing elements in a slice.
        // However, detecting these reliably requires an optimal differencing
        // algorithm, for which diff.Difference is not.
        //
        // Instead, we first iterate through both slices to detect which elements
        // would be ignored if standing alone. The index of non-discarded elements
        // are stored in a separate slice, which diffing is then performed on.
        var indexesX, indexesY []int
        var ignoredX, ignoredY []bool
        for ix := 0; ix < vx.Len(); ix++ {
                ignored := s.statelessCompare(withIndexes(ix, -1)).NumDiff == 0
                if !ignored {
                        indexesX = append(indexesX, ix)
                }
                ignoredX = append(ignoredX, ignored)
        }
        for iy := 0; iy < vy.Len(); iy++ {
                ignored := s.statelessCompare(withIndexes(-1, iy)).NumDiff == 0
                if !ignored {
                        indexesY = append(indexesY, iy)
                }
                ignoredY = append(ignoredY, ignored)
        }

        // Compute an edit-script for slices vx and vy (excluding ignored elements).
        edits := diff.Difference(len(indexesX), len(indexesY), func(ix, iy int) diff.Result {
                return s.statelessCompare(withIndexes(indexesX[ix], indexesY[iy]))
        })

        // Replay the ignore-scripts and the edit-script.
        var ix, iy int
        for ix < vx.Len() || iy < vy.Len() {
                var e diff.EditType
                switch {
                case ix < len(ignoredX) && ignoredX[ix]:
                        e = diff.UniqueX
                case iy < len(ignoredY) && ignoredY[iy]:
                        e = diff.UniqueY
                default:
                        e, edits = edits[0], edits[1:]
                }
                switch e {
                case diff.UniqueX:
                        s.compareAny(withIndexes(ix, -1))
                        ix++
                case diff.UniqueY:
                        s.compareAny(withIndexes(-1, iy))
                        iy++
                default:
                        s.compareAny(withIndexes(ix, iy))
                        ix++
                        iy++
                }
        }
}

func (s *state) compareMap(t reflect.Type, vx, vy reflect.Value) {
        if vx.IsNil() || vy.IsNil() {
                s.report(vx.IsNil() && vy.IsNil(), 0)
                return
        }

        // Cycle-detection for maps.
        if eq, visited := s.curPtrs.Push(vx, vy); visited {
                s.report(eq, reportByCycle)
                return
        }
        defer s.curPtrs.Pop(vx, vy)

        // We combine and sort the two map keys so that we can perform the
        // comparisons in a deterministic order.
        step := MapIndex{&mapIndex{pathStep: pathStep{typ: t.Elem()}}}
        for _, k := range value.SortKeys(append(vx.MapKeys(), vy.MapKeys()...)) {
                step.vx = vx.MapIndex(k)
                step.vy = vy.MapIndex(k)
                step.key = k
                if !step.vx.IsValid() && !step.vy.IsValid() {
                        // It is possible for both vx and vy to be invalid if the
                        // key contained a NaN value in it.
                        //
                        // Even with the ability to retrieve NaN keys in Go 1.12,
                        // there still isn't a sensible way to compare the values since
                        // a NaN key may map to multiple unordered values.
                        // The most reasonable way to compare NaNs would be to compare the
                        // set of values. However, this is impossible to do efficiently
                        // since set equality is provably an O(n^2) operation given only
                        // an Equal function. If we had a Less function or Hash function,
                        // this could be done in O(n*log(n)) or O(n), respectively.
                        //
                        // Rather than adding complex logic to deal with NaNs, make it
                        // the user's responsibility to compare such obscure maps.
                        const help = "consider providing a Comparer to compare the map"
                        panic(fmt.Sprintf("%#v has map key with NaNs\n%s", s.curPath, help))
                }
                s.compareAny(step)
        }
}

func (s *state) comparePtr(t reflect.Type, vx, vy reflect.Value) {
        if vx.IsNil() || vy.IsNil() {
                s.report(vx.IsNil() && vy.IsNil(), 0)
                return
        }

        // Cycle-detection for pointers.
        if eq, visited := s.curPtrs.Push(vx, vy); visited {
                s.report(eq, reportByCycle)
                return
        }
        defer s.curPtrs.Pop(vx, vy)

        vx, vy = vx.Elem(), vy.Elem()
        s.compareAny(Indirect{&indirect{pathStep{t.Elem(), vx, vy}}})
}

func (s *state) compareInterface(t reflect.Type, vx, vy reflect.Value) {
        if vx.IsNil() || vy.IsNil() {
                s.report(vx.IsNil() && vy.IsNil(), 0)
                return
        }
        vx, vy = vx.Elem(), vy.Elem()
        if vx.Type() != vy.Type() {
                s.report(false, 0)
                return
        }
        s.compareAny(TypeAssertion{&typeAssertion{pathStep{vx.Type(), vx, vy}}})
}

func (s *state) report(eq bool, rf resultFlags) {
        if rf&reportByIgnore == 0 {
                if eq {
                        s.result.NumSame++
                        rf |= reportEqual
                } else {
                        s.result.NumDiff++
                        rf |= reportUnequal
                }
        }
        for _, r := range s.reporters {
                r.Report(Result{flags: rf})
        }
}

// recChecker tracks the state needed to periodically perform checks that
// user provided transformers are not stuck in an infinitely recursive cycle.
type recChecker struct{ next int }

// Check scans the Path for any recursive transformers and panics when any
// recursive transformers are detected. Note that the presence of a
// recursive Transformer does not necessarily imply an infinite cycle.
// As such, this check only activates after some minimal number of path steps.
func (rc *recChecker) Check(p Path) {
        const minLen = 1 << 16
        if rc.next == 0 {
                rc.next = minLen
        }
        if len(p) < rc.next {
                return
        }
        rc.next <<= 1

        // Check whether the same transformer has appeared at least twice.
        var ss []string
        m := map[Option]int{}
        for _, ps := range p {
                if t, ok := ps.(Transform); ok {
                        t := t.Option()
                        if m[t] == 1 { // Transformer was used exactly once before
                                tf := t.(*transformer).fnc.Type()
                                ss = append(ss, fmt.Sprintf("%v: %v => %v", t, tf.In(0), tf.Out(0)))
                        }
                        m[t]++
                }
        }
        if len(ss) > 0 {
                const warning = "recursive set of Transformers detected"
                const help = "consider using cmpopts.AcyclicTransformer"
                set := strings.Join(ss, "\n\t")
                panic(fmt.Sprintf("%s:\n\t%s\n%s", warning, set, help))
        }
}

// dynChecker tracks the state needed to periodically perform checks that
// user provided functions are symmetric and deterministic.
// The zero value is safe for immediate use.
type dynChecker struct{ curr, next int }

// Next increments the state and reports whether a check should be performed.
//
// Checks occur every Nth function call, where N is a triangular number:
//      0 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171 190 ...
// See https://en.wikipedia.org/wiki/Triangular_number
//
// This sequence ensures that the cost of checks drops significantly as
// the number of functions calls grows larger.
func (dc *dynChecker) Next() bool {
        ok := dc.curr == dc.next
        if ok {
                dc.curr = 0
                dc.next++
        }
        dc.curr++
        return ok
}

// makeAddressable returns a value that is always addressable.
// It returns the input verbatim if it is already addressable,
// otherwise it creates a new value and returns an addressable copy.
func makeAddressable(v reflect.Value) reflect.Value {
        if v.CanAddr() {
                return v
        }
        vc := reflect.New(v.Type()).Elem()
        vc.Set(v)
        return vc
}