tools: Shuffle go code into an idiomatic tree

main packages usually go under a `cmd` directory.
Hoist utility packages to the root `src` directroy so they can be shared.

Change-Id: I0c221f6cd39980f5c202c030cd5134d775533efa
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50901
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

tools/src/glob/glob.go

@@ -0,0 +1,185 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package glob provides file globbing utilities
+package glob
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"dawn.googlesource.com/tint/tools/src/match"
+)
+
+// Scan walks all files and subdirectories from root, returning those
+// that Config.shouldExamine() returns true for.
+func Scan(root string, cfg Config) ([]string, error) {
+	files := []string{}
+	err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+		rel, err := filepath.Rel(root, path)
+		if err != nil {
+			rel = path
+		}
+
+		if rel == ".git" {
+			return filepath.SkipDir
+		}
+
+		if !cfg.shouldExamine(root, path) {
+			return nil
+		}
+
+		if !info.IsDir() {
+			files = append(files, rel)
+		}
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return files, nil
+}
+
+// Configs is a slice of Config.
+type Configs []Config
+
+// Config is used to parse the JSON configuration file.
+type Config struct {
+	// Paths holds a number of JSON objects that contain either a "includes" or
+	// "excludes" key to an array of path patterns.
+	// Each path pattern is considered in turn to either include or exclude the
+	// file path for license scanning. Pattern use forward-slashes '/' for
+	// directory separators, and may use the following wildcards:
+	//  ?  - matches any single non-separator character
+	//  *  - matches any sequence of non-separator characters
+	//  ** - matches any sequence of characters including separators
+	//
+	// Rules are processed in the order in which they are declared, with later
+	// rules taking precedence over earlier rules.
+	//
+	// All files are excluded before the first rule is evaluated.
+	//
+	// Example:
+	//
+	// {
+	//   "paths": [
+	// 	  { "exclude": [ "out/*", "build/*" ] },
+	// 	  { "include": [ "out/foo.txt" ] }
+	//   ],
+	// }
+	Paths searchRules
+}
+
+// LoadConfig loads a config file at path.
+func LoadConfig(path string) (Config, error) {
+	cfgBody, err := ioutil.ReadFile(path)
+	if err != nil {
+		return Config{}, err
+	}
+	d := json.NewDecoder(bytes.NewReader(cfgBody))
+	cfg := Config{}
+	if err := d.Decode(&cfg); err != nil {
+		return Config{}, err
+	}
+	return cfg, nil
+}
+
+// rule is a search path predicate.
+// root is the project relative path.
+// cond is the value to return if the rule doesn't either include or exclude.
+type rule func(path string, cond bool) bool
+
+// searchRules is a ordered list of search rules.
+// searchRules is its own type as it has to perform custom JSON unmarshalling.
+type searchRules []rule
+
+// UnmarshalJSON unmarshals the array of rules in the form:
+// { "include": [ ... ] } or { "exclude": [ ... ] }
+func (l *searchRules) UnmarshalJSON(body []byte) error {
+	type parsed struct {
+		Include []string
+		Exclude []string
+	}
+
+	p := []parsed{}
+	if err := json.NewDecoder(bytes.NewReader(body)).Decode(&p); err != nil {
+		return err
+	}
+
+	*l = searchRules{}
+	for _, rule := range p {
+		rule := rule
+		switch {
+		case len(rule.Include) > 0 && len(rule.Exclude) > 0:
+			return fmt.Errorf("Rule cannot contain both include and exclude")
+		case len(rule.Include) > 0:
+			tests := make([]match.Test, len(rule.Include))
+			for i, pattern := range rule.Include {
+				test, err := match.New(pattern)
+				if err != nil {
+					return err
+				}
+				tests[i] = test
+			}
+			*l = append(*l, func(path string, cond bool) bool {
+				for _, test := range tests {
+					if test(path) {
+						return true
+					}
+				}
+				return cond
+			})
+		case len(rule.Exclude) > 0:
+			tests := make([]match.Test, len(rule.Exclude))
+			for i, pattern := range rule.Exclude {
+				test, err := match.New(pattern)
+				if err != nil {
+					return err
+				}
+				tests[i] = test
+			}
+			*l = append(*l, func(path string, cond bool) bool {
+				for _, test := range tests {
+					if test(path) {
+						return false
+					}
+				}
+				return cond
+			})
+		}
+	}
+	return nil
+}
+
+// shouldExamine returns true if the file at absPath should be scanned.
+func (c Config) shouldExamine(root, absPath string) bool {
+	root = filepath.ToSlash(root)       // Canonicalize
+	absPath = filepath.ToSlash(absPath) // Canonicalize
+	relPath, err := filepath.Rel(root, absPath)
+	if err != nil {
+		return false
+	}
+
+	res := false
+	for _, rule := range c.Paths {
+		res = rule(relPath, res)
+	}
+
+	return res
+}