Speed up git diff highlight generation (#16180)

Co-authored-by: Mura Li <typeless@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>

go.mod

@@ -59,6 +59,7 @@ require (
 	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
 	github.com/hashicorp/go-retryablehttp v0.7.0 // indirect
 	github.com/hashicorp/go-version v1.3.1
+	github.com/hashicorp/golang-lru v0.5.1
 	github.com/huandu/xstrings v1.3.2
 	github.com/issue9/identicon v1.2.0
 	github.com/jaytaylor/html2text v0.0.0-20200412013138-3577fbdbcff7

go.sum

@@ -593,6 +593,7 @@ github.com/hashicorp/go-uuid v1.0.0/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/b
 github.com/hashicorp/go-uuid v1.0.1/go.mod h1:6SBZvOh/SIDV7/2o3Jml5SYk/TvGqwFJ/bN7x4byOro=
 github.com/hashicorp/go.net v0.0.1/go.mod h1:hjKkEWcCURg++eb33jQU7oqQcI9XDCnUzHA0oac0k90=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
+github.com/hashicorp/golang-lru v0.5.1 h1:0hERBMJE1eitiLkihrMvRVBYAkpHzc/J3QdDN+dAcgU=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=

modules/highlight/highlight.go

@@ -8,6 +8,7 @@ package highlight
 import (
 	"bufio"
 	"bytes"
+	"fmt"
 	gohtml "html"
 	"path/filepath"
 	"strings"
@@ -20,6 +21,7 @@ import (
 	"github.com/alecthomas/chroma/formatters/html"
 	"github.com/alecthomas/chroma/lexers"
 	"github.com/alecthomas/chroma/styles"
+	lru "github.com/hashicorp/golang-lru"
 )
 
 // don't index files larger than this many bytes for performance purposes
@@ -30,6 +32,8 @@ var (
 	highlightMapping = map[string]string{}
 
 	once sync.Once
+
+	cache *lru.ARCCache
 )
 
 // NewContext loads custom highlight map from local config
@@ -39,6 +43,13 @@ func NewContext() {
 		for i := range keys {
 			highlightMapping[keys[i].Name()] = keys[i].Value()
 		}
+
+		// The size 512 is simply a conservative rule of thumb
+		c, err := lru.NewARC(512)
+		if err != nil {
+			panic(fmt.Sprintf("failed to initialize LRU cache for highlighter: %s", err))
+		}
+		cache = c
 	})
 }
 
@@ -73,11 +84,18 @@ func Code(fileName, code string) string {
 		lexer = lexers.Get(val)
 	}
 
+	if lexer == nil {
+		if l, ok := cache.Get(fileName); ok {
+			lexer = l.(chroma.Lexer)
+		}
+	}
+
 	if lexer == nil {
 		lexer = lexers.Match(fileName)
 		if lexer == nil {
 			lexer = lexers.Fallback
 		}
+		cache.Add(fileName, lexer)
 	}
 
 	iterator, err := lexer.Tokenise(nil, string(code))

vendor/github.com/hashicorp/golang-lru/.gitignore

@@ -0,0 +1,23 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test

vendor/github.com/hashicorp/golang-lru/2q.go

@@ -0,0 +1,223 @@
+package lru
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/hashicorp/golang-lru/simplelru"
+)
+
+const (
+	// Default2QRecentRatio is the ratio of the 2Q cache dedicated
+	// to recently added entries that have only been accessed once.
+	Default2QRecentRatio = 0.25
+
+	// Default2QGhostEntries is the default ratio of ghost
+	// entries kept to track entries recently evicted
+	Default2QGhostEntries = 0.50
+)
+
+// TwoQueueCache is a thread-safe fixed size 2Q cache.
+// 2Q is an enhancement over the standard LRU cache
+// in that it tracks both frequently and recently used
+// entries separately. This avoids a burst in access to new
+// entries from evicting frequently used entries. It adds some
+// additional tracking overhead to the standard LRU cache, and is
+// computationally about 2x the cost, and adds some metadata over
+// head. The ARCCache is similar, but does not require setting any
+// parameters.
+type TwoQueueCache struct {
+	size       int
+	recentSize int
+
+	recent      simplelru.LRUCache
+	frequent    simplelru.LRUCache
+	recentEvict simplelru.LRUCache
+	lock        sync.RWMutex
+}
+
+// New2Q creates a new TwoQueueCache using the default
+// values for the parameters.
+func New2Q(size int) (*TwoQueueCache, error) {
+	return New2QParams(size, Default2QRecentRatio, Default2QGhostEntries)
+}
+
+// New2QParams creates a new TwoQueueCache using the provided
+// parameter values.
+func New2QParams(size int, recentRatio float64, ghostRatio float64) (*TwoQueueCache, error) {
+	if size <= 0 {
+		return nil, fmt.Errorf("invalid size")
+	}
+	if recentRatio < 0.0 || recentRatio > 1.0 {
+		return nil, fmt.Errorf("invalid recent ratio")
+	}
+	if ghostRatio < 0.0 || ghostRatio > 1.0 {
+		return nil, fmt.Errorf("invalid ghost ratio")
+	}
+
+	// Determine the sub-sizes
+	recentSize := int(float64(size) * recentRatio)
+	evictSize := int(float64(size) * ghostRatio)
+
+	// Allocate the LRUs
+	recent, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+	frequent, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+	recentEvict, err := simplelru.NewLRU(evictSize, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	// Initialize the cache
+	c := &TwoQueueCache{
+		size:        size,
+		recentSize:  recentSize,
+		recent:      recent,
+		frequent:    frequent,
+		recentEvict: recentEvict,
+	}
+	return c, nil
+}
+
+// Get looks up a key's value from the cache.
+func (c *TwoQueueCache) Get(key interface{}) (value interface{}, ok bool) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Check if this is a frequent value
+	if val, ok := c.frequent.Get(key); ok {
+		return val, ok
+	}
+
+	// If the value is contained in recent, then we
+	// promote it to frequent
+	if val, ok := c.recent.Peek(key); ok {
+		c.recent.Remove(key)
+		c.frequent.Add(key, val)
+		return val, ok
+	}
+
+	// No hit
+	return nil, false
+}
+
+// Add adds a value to the cache.
+func (c *TwoQueueCache) Add(key, value interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Check if the value is frequently used already,
+	// and just update the value
+	if c.frequent.Contains(key) {
+		c.frequent.Add(key, value)
+		return
+	}
+
+	// Check if the value is recently used, and promote
+	// the value into the frequent list
+	if c.recent.Contains(key) {
+		c.recent.Remove(key)
+		c.frequent.Add(key, value)
+		return
+	}
+
+	// If the value was recently evicted, add it to the
+	// frequently used list
+	if c.recentEvict.Contains(key) {
+		c.ensureSpace(true)
+		c.recentEvict.Remove(key)
+		c.frequent.Add(key, value)
+		return
+	}
+
+	// Add to the recently seen list
+	c.ensureSpace(false)
+	c.recent.Add(key, value)
+	return
+}
+
+// ensureSpace is used to ensure we have space in the cache
+func (c *TwoQueueCache) ensureSpace(recentEvict bool) {
+	// If we have space, nothing to do
+	recentLen := c.recent.Len()
+	freqLen := c.frequent.Len()
+	if recentLen+freqLen < c.size {
+		return
+	}
+
+	// If the recent buffer is larger than
+	// the target, evict from there
+	if recentLen > 0 && (recentLen > c.recentSize || (recentLen == c.recentSize && !recentEvict)) {
+		k, _, _ := c.recent.RemoveOldest()
+		c.recentEvict.Add(k, nil)
+		return
+	}
+
+	// Remove from the frequent list otherwise
+	c.frequent.RemoveOldest()
+}
+
+// Len returns the number of items in the cache.
+func (c *TwoQueueCache) Len() int {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	return c.recent.Len() + c.frequent.Len()
+}
+
+// Keys returns a slice of the keys in the cache.
+// The frequently used keys are first in the returned slice.
+func (c *TwoQueueCache) Keys() []interface{} {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	k1 := c.frequent.Keys()
+	k2 := c.recent.Keys()
+	return append(k1, k2...)
+}
+
+// Remove removes the provided key from the cache.
+func (c *TwoQueueCache) Remove(key interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	if c.frequent.Remove(key) {
+		return
+	}
+	if c.recent.Remove(key) {
+		return
+	}
+	if c.recentEvict.Remove(key) {
+		return
+	}
+}
+
+// Purge is used to completely clear the cache.
+func (c *TwoQueueCache) Purge() {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	c.recent.Purge()
+	c.frequent.Purge()
+	c.recentEvict.Purge()
+}
+
+// Contains is used to check if the cache contains a key
+// without updating recency or frequency.
+func (c *TwoQueueCache) Contains(key interface{}) bool {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	return c.frequent.Contains(key) || c.recent.Contains(key)
+}
+
+// Peek is used to inspect the cache value of a key
+// without updating recency or frequency.
+func (c *TwoQueueCache) Peek(key interface{}) (value interface{}, ok bool) {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	if val, ok := c.frequent.Peek(key); ok {
+		return val, ok
+	}
+	return c.recent.Peek(key)
+}

vendor/github.com/hashicorp/golang-lru/README.md

@@ -0,0 +1,25 @@
+golang-lru
+==========
+
+This provides the `lru` package which implements a fixed-size
+thread safe LRU cache. It is based on the cache in Groupcache.
+
+Documentation
+=============
+
+Full docs are available on [Godoc](http://godoc.org/github.com/hashicorp/golang-lru)
+
+Example
+=======
+
+Using the LRU is very simple:
+
+```go
+l, _ := New(128)
+for i := 0; i < 256; i++ {
+    l.Add(i, nil)
+}
+if l.Len() != 128 {
+    panic(fmt.Sprintf("bad len: %v", l.Len()))
+}
+```

vendor/github.com/hashicorp/golang-lru/arc.go

@@ -0,0 +1,257 @@
+package lru
+
+import (
+	"sync"
+
+	"github.com/hashicorp/golang-lru/simplelru"
+)
+
+// ARCCache is a thread-safe fixed size Adaptive Replacement Cache (ARC).
+// ARC is an enhancement over the standard LRU cache in that tracks both
+// frequency and recency of use. This avoids a burst in access to new
+// entries from evicting the frequently used older entries. It adds some
+// additional tracking overhead to a standard LRU cache, computationally
+// it is roughly 2x the cost, and the extra memory overhead is linear
+// with the size of the cache. ARC has been patented by IBM, but is
+// similar to the TwoQueueCache (2Q) which requires setting parameters.
+type ARCCache struct {
+	size int // Size is the total capacity of the cache
+	p    int // P is the dynamic preference towards T1 or T2
+
+	t1 simplelru.LRUCache // T1 is the LRU for recently accessed items
+	b1 simplelru.LRUCache // B1 is the LRU for evictions from t1
+
+	t2 simplelru.LRUCache // T2 is the LRU for frequently accessed items
+	b2 simplelru.LRUCache // B2 is the LRU for evictions from t2
+
+	lock sync.RWMutex
+}
+
+// NewARC creates an ARC of the given size
+func NewARC(size int) (*ARCCache, error) {
+	// Create the sub LRUs
+	b1, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+	b2, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+	t1, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+	t2, err := simplelru.NewLRU(size, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	// Initialize the ARC
+	c := &ARCCache{
+		size: size,
+		p:    0,
+		t1:   t1,
+		b1:   b1,
+		t2:   t2,
+		b2:   b2,
+	}
+	return c, nil
+}
+
+// Get looks up a key's value from the cache.
+func (c *ARCCache) Get(key interface{}) (value interface{}, ok bool) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// If the value is contained in T1 (recent), then
+	// promote it to T2 (frequent)
+	if val, ok := c.t1.Peek(key); ok {
+		c.t1.Remove(key)
+		c.t2.Add(key, val)
+		return val, ok
+	}
+
+	// Check if the value is contained in T2 (frequent)
+	if val, ok := c.t2.Get(key); ok {
+		return val, ok
+	}
+
+	// No hit
+	return nil, false
+}
+
+// Add adds a value to the cache.
+func (c *ARCCache) Add(key, value interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Check if the value is contained in T1 (recent), and potentially
+	// promote it to frequent T2
+	if c.t1.Contains(key) {
+		c.t1.Remove(key)
+		c.t2.Add(key, value)
+		return
+	}
+
+	// Check if the value is already in T2 (frequent) and update it
+	if c.t2.Contains(key) {
+		c.t2.Add(key, value)
+		return
+	}
+
+	// Check if this value was recently evicted as part of the
+	// recently used list
+	if c.b1.Contains(key) {
+		// T1 set is too small, increase P appropriately
+		delta := 1
+		b1Len := c.b1.Len()
+		b2Len := c.b2.Len()
+		if b2Len > b1Len {
+			delta = b2Len / b1Len
+		}
+		if c.p+delta >= c.size {
+			c.p = c.size
+		} else {
+			c.p += delta
+		}
+
+		// Potentially need to make room in the cache
+		if c.t1.Len()+c.t2.Len() >= c.size {
+			c.replace(false)
+		}
+
+		// Remove from B1
+		c.b1.Remove(key)
+
+		// Add the key to the frequently used list
+		c.t2.Add(key, value)
+		return
+	}
+
+	// Check if this value was recently evicted as part of the
+	// frequently used list
+	if c.b2.Contains(key) {
+		// T2 set is too small, decrease P appropriately
+		delta := 1
+		b1Len := c.b1.Len()
+		b2Len := c.b2.Len()
+		if b1Len > b2Len {
+			delta = b1Len / b2Len
+		}
+		if delta >= c.p {
+			c.p = 0
+		} else {
+			c.p -= delta
+		}
+
+		// Potentially need to make room in the cache
+		if c.t1.Len()+c.t2.Len() >= c.size {
+			c.replace(true)
+		}
+
+		// Remove from B2
+		c.b2.Remove(key)
+
+		// Add the key to the frequently used list
+		c.t2.Add(key, value)
+		return
+	}
+
+	// Potentially need to make room in the cache
+	if c.t1.Len()+c.t2.Len() >= c.size {
+		c.replace(false)
+	}
+
+	// Keep the size of the ghost buffers trim
+	if c.b1.Len() > c.size-c.p {
+		c.b1.RemoveOldest()
+	}
+	if c.b2.Len() > c.p {
+		c.b2.RemoveOldest()
+	}
+
+	// Add to the recently seen list
+	c.t1.Add(key, value)
+	return
+}
+
+// replace is used to adaptively evict from either T1 or T2
+// based on the current learned value of P
+func (c *ARCCache) replace(b2ContainsKey bool) {
+	t1Len := c.t1.Len()
+	if t1Len > 0 && (t1Len > c.p || (t1Len == c.p && b2ContainsKey)) {
+		k, _, ok := c.t1.RemoveOldest()
+		if ok {
+			c.b1.Add(k, nil)
+		}
+	} else {
+		k, _, ok := c.t2.RemoveOldest()
+		if ok {
+			c.b2.Add(k, nil)
+		}
+	}
+}
+
+// Len returns the number of cached entries
+func (c *ARCCache) Len() int {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	return c.t1.Len() + c.t2.Len()
+}
+
+// Keys returns all the cached keys
+func (c *ARCCache) Keys() []interface{} {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	k1 := c.t1.Keys()
+	k2 := c.t2.Keys()
+	return append(k1, k2...)
+}
+
+// Remove is used to purge a key from the cache
+func (c *ARCCache) Remove(key interface{}) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	if c.t1.Remove(key) {
+		return
+	}
+	if c.t2.Remove(key) {
+		return
+	}
+	if c.b1.Remove(key) {
+		return
+	}
+	if c.b2.Remove(key) {
+		return
+	}
+}
+
+// Purge is used to clear the cache
+func (c *ARCCache) Purge() {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	c.t1.Purge()
+	c.t2.Purge()
+	c.b1.Purge()
+	c.b2.Purge()
+}
+
+// Contains is used to check if the cache contains a key
+// without updating recency or frequency.
+func (c *ARCCache) Contains(key interface{}) bool {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	return c.t1.Contains(key) || c.t2.Contains(key)
+}
+
+// Peek is used to inspect the cache value of a key
+// without updating recency or frequency.
+func (c *ARCCache) Peek(key interface{}) (value interface{}, ok bool) {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	if val, ok := c.t1.Peek(key); ok {
+		return val, ok
+	}
+	return c.t2.Peek(key)
+}

vendor/github.com/hashicorp/golang-lru/doc.go

@@ -0,0 +1,21 @@
+// Package lru provides three different LRU caches of varying sophistication.
+//
+// Cache is a simple LRU cache. It is based on the
+// LRU implementation in groupcache:
+// https://github.com/golang/groupcache/tree/master/lru
+//
+// TwoQueueCache tracks frequently used and recently used entries separately.
+// This avoids a burst of accesses from taking out frequently used entries,
+// at the cost of about 2x computational overhead and some extra bookkeeping.
+//
+// ARCCache is an adaptive replacement cache. It tracks recent evictions as
+// well as recent usage in both the frequent and recent caches. Its
+// computational overhead is comparable to TwoQueueCache, but the memory
+// overhead is linear with the size of the cache.
+//
+// ARC has been patented by IBM, so do not use it if that is problematic for
+// your program.
+//
+// All caches in this package take locks while operating, and are therefore
+// thread-safe for consumers.
+package lru

vendor/github.com/hashicorp/golang-lru/go.mod

@@ -0,0 +1 @@
+module github.com/hashicorp/golang-lru

vendor/github.com/hashicorp/golang-lru/lru.go

@@ -0,0 +1,116 @@
+package lru
+
+import (
+	"sync"
+
+	"github.com/hashicorp/golang-lru/simplelru"
+)
+
+// Cache is a thread-safe fixed size LRU cache.
+type Cache struct {
+	lru  simplelru.LRUCache
+	lock sync.RWMutex
+}
+
+// New creates an LRU of the given size.
+func New(size int) (*Cache, error) {
+	return NewWithEvict(size, nil)
+}
+
+// NewWithEvict constructs a fixed size cache with the given eviction
+// callback.
+func NewWithEvict(size int, onEvicted func(key interface{}, value interface{})) (*Cache, error) {
+	lru, err := simplelru.NewLRU(size, simplelru.EvictCallback(onEvicted))
+	if err != nil {
+		return nil, err
+	}
+	c := &Cache{
+		lru: lru,
+	}
+	return c, nil
+}
+
+// Purge is used to completely clear the cache.
+func (c *Cache) Purge() {
+	c.lock.Lock()
+	c.lru.Purge()
+	c.lock.Unlock()
+}
+
+// Add adds a value to the cache.  Returns true if an eviction occurred.
+func (c *Cache) Add(key, value interface{}) (evicted bool) {
+	c.lock.Lock()
+	evicted = c.lru.Add(key, value)
+	c.lock.Unlock()
+	return evicted
+}
+
+// Get looks up a key's value from the cache.
+func (c *Cache) Get(key interface{}) (value interface{}, ok bool) {
+	c.lock.Lock()
+	value, ok = c.lru.Get(key)
+	c.lock.Unlock()
+	return value, ok
+}
+
+// Contains checks if a key is in the cache, without updating the
+// recent-ness or deleting it for being stale.
+func (c *Cache) Contains(key interface{}) bool {
+	c.lock.RLock()
+	containKey := c.lru.Contains(key)
+	c.lock.RUnlock()
+	return containKey
+}
+
+// Peek returns the key value (or undefined if not found) without updating
+// the "recently used"-ness of the key.
+func (c *Cache) Peek(key interface{}) (value interface{}, ok bool) {
+	c.lock.RLock()
+	value, ok = c.lru.Peek(key)
+	c.lock.RUnlock()
+	return value, ok
+}
+
+// ContainsOrAdd checks if a key is in the cache  without updating the
+// recent-ness or deleting it for being stale,  and if not, adds the value.
+// Returns whether found and whether an eviction occurred.
+func (c *Cache) ContainsOrAdd(key, value interface{}) (ok, evicted bool) {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	if c.lru.Contains(key) {
+		return true, false
+	}
+	evicted = c.lru.Add(key, value)
+	return false, evicted
+}
+
+// Remove removes the provided key from the cache.
+func (c *Cache) Remove(key interface{}) {
+	c.lock.Lock()
+	c.lru.Remove(key)
+	c.lock.Unlock()
+}
+
+// RemoveOldest removes the oldest item from the cache.
+func (c *Cache) RemoveOldest() {
+	c.lock.Lock()
+	c.lru.RemoveOldest()
+	c.lock.Unlock()
+}
+
+// Keys returns a slice of the keys in the cache, from oldest to newest.
+func (c *Cache) Keys() []interface{} {
+	c.lock.RLock()
+	keys := c.lru.Keys()
+	c.lock.RUnlock()
+	return keys
+}
+
+// Len returns the number of items in the cache.
+func (c *Cache) Len() int {
+	c.lock.RLock()
+	length := c.lru.Len()
+	c.lock.RUnlock()
+	return length
+}

vendor/github.com/hashicorp/golang-lru/simplelru/lru.go

@@ -0,0 +1,161 @@
+package simplelru
+
+import (
+	"container/list"
+	"errors"
+)
+
+// EvictCallback is used to get a callback when a cache entry is evicted
+type EvictCallback func(key interface{}, value interface{})
+
+// LRU implements a non-thread safe fixed size LRU cache
+type LRU struct {
+	size      int
+	evictList *list.List
+	items     map[interface{}]*list.Element
+	onEvict   EvictCallback
+}
+
+// entry is used to hold a value in the evictList
+type entry struct {
+	key   interface{}
+	value interface{}
+}
+
+// NewLRU constructs an LRU of the given size
+func NewLRU(size int, onEvict EvictCallback) (*LRU, error) {
+	if size <= 0 {
+		return nil, errors.New("Must provide a positive size")
+	}
+	c := &LRU{
+		size:      size,
+		evictList: list.New(),
+		items:     make(map[interface{}]*list.Element),
+		onEvict:   onEvict,
+	}
+	return c, nil
+}
+
+// Purge is used to completely clear the cache.
+func (c *LRU) Purge() {
+	for k, v := range c.items {
+		if c.onEvict != nil {
+			c.onEvict(k, v.Value.(*entry).value)
+		}
+		delete(c.items, k)
+	}
+	c.evictList.Init()
+}
+
+// Add adds a value to the cache.  Returns true if an eviction occurred.
+func (c *LRU) Add(key, value interface{}) (evicted bool) {
+	// Check for existing item
+	if ent, ok := c.items[key]; ok {
+		c.evictList.MoveToFront(ent)
+		ent.Value.(*entry).value = value
+		return false
+	}
+
+	// Add new item
+	ent := &entry{key, value}
+	entry := c.evictList.PushFront(ent)
+	c.items[key] = entry
+
+	evict := c.evictList.Len() > c.size
+	// Verify size not exceeded
+	if evict {
+		c.removeOldest()
+	}
+	return evict
+}
+
+// Get looks up a key's value from the cache.
+func (c *LRU) Get(key interface{}) (value interface{}, ok bool) {
+	if ent, ok := c.items[key]; ok {
+		c.evictList.MoveToFront(ent)
+		return ent.Value.(*entry).value, true
+	}
+	return
+}
+
+// Contains checks if a key is in the cache, without updating the recent-ness
+// or deleting it for being stale.
+func (c *LRU) Contains(key interface{}) (ok bool) {
+	_, ok = c.items[key]
+	return ok
+}
+
+// Peek returns the key value (or undefined if not found) without updating
+// the "recently used"-ness of the key.
+func (c *LRU) Peek(key interface{}) (value interface{}, ok bool) {
+	var ent *list.Element
+	if ent, ok = c.items[key]; ok {
+		return ent.Value.(*entry).value, true
+	}
+	return nil, ok
+}
+
+// Remove removes the provided key from the cache, returning if the
+// key was contained.
+func (c *LRU) Remove(key interface{}) (present bool) {
+	if ent, ok := c.items[key]; ok {
+		c.removeElement(ent)
+		return true
+	}
+	return false
+}
+
+// RemoveOldest removes the oldest item from the cache.
+func (c *LRU) RemoveOldest() (key interface{}, value interface{}, ok bool) {
+	ent := c.evictList.Back()
+	if ent != nil {
+		c.removeElement(ent)
+		kv := ent.Value.(*entry)
+		return kv.key, kv.value, true
+	}
+	return nil, nil, false
+}
+
+// GetOldest returns the oldest entry
+func (c *LRU) GetOldest() (key interface{}, value interface{}, ok bool) {
+	ent := c.evictList.Back()
+	if ent != nil {
+		kv := ent.Value.(*entry)
+		return kv.key, kv.value, true
+	}
+	return nil, nil, false
+}
+
+// Keys returns a slice of the keys in the cache, from oldest to newest.
+func (c *LRU) Keys() []interface{} {
+	keys := make([]interface{}, len(c.items))
+	i := 0
+	for ent := c.evictList.Back(); ent != nil; ent = ent.Prev() {
+		keys[i] = ent.Value.(*entry).key
+		i++
+	}
+	return keys
+}
+
+// Len returns the number of items in the cache.
+func (c *LRU) Len() int {
+	return c.evictList.Len()
+}
+
+// removeOldest removes the oldest item from the cache.
+func (c *LRU) removeOldest() {
+	ent := c.evictList.Back()
+	if ent != nil {
+		c.removeElement(ent)
+	}
+}
+
+// removeElement is used to remove a given list element from the cache
+func (c *LRU) removeElement(e *list.Element) {
+	c.evictList.Remove(e)
+	kv := e.Value.(*entry)
+	delete(c.items, kv.key)
+	if c.onEvict != nil {
+		c.onEvict(kv.key, kv.value)
+	}
+}

vendor/github.com/hashicorp/golang-lru/simplelru/lru_interface.go

@@ -0,0 +1,36 @@
+package simplelru
+
+// LRUCache is the interface for simple LRU cache.
+type LRUCache interface {
+	// Adds a value to the cache, returns true if an eviction occurred and
+	// updates the "recently used"-ness of the key.
+	Add(key, value interface{}) bool
+
+	// Returns key's value from the cache and
+	// updates the "recently used"-ness of the key. #value, isFound
+	Get(key interface{}) (value interface{}, ok bool)
+
+	// Check if a key exsists in cache without updating the recent-ness.
+	Contains(key interface{}) (ok bool)
+
+	// Returns key's value without updating the "recently used"-ness of the key.
+	Peek(key interface{}) (value interface{}, ok bool)
+
+	// Removes a key from the cache.
+	Remove(key interface{}) bool
+
+	// Removes the oldest entry from cache.
+	RemoveOldest() (interface{}, interface{}, bool)
+
+	// Returns the oldest entry from the cache. #key, value, isFound
+	GetOldest() (interface{}, interface{}, bool)
+
+	// Returns a slice of the keys in the cache, from oldest to newest.
+	Keys() []interface{}
+
+	// Returns the number of items in the cache.
+	Len() int
+
+	// Clear all cache entries
+	Purge()
+}

vendor/modules.txt

@@ -467,6 +467,10 @@ github.com/hashicorp/go-retryablehttp
 # github.com/hashicorp/go-version v1.3.1 => github.com/6543/go-version v1.3.1
 ## explicit
 github.com/hashicorp/go-version
+# github.com/hashicorp/golang-lru v0.5.1
+## explicit
+github.com/hashicorp/golang-lru
+github.com/hashicorp/golang-lru/simplelru
 # github.com/hashicorp/hcl v1.0.0
 github.com/hashicorp/hcl
 github.com/hashicorp/hcl/hcl/ast