Fix include search path logic (#31)

This reverts part of the changes introduced in #24: we want to include
the file's directory in our search path, not the process's current
working directory.

In fixing this, I realized that we can simply build the list of search
directories once as part of the linting context. This further simplifies
the downstream code while also making this less error prone.

check.go

@@ -167,7 +167,7 @@ next:
 // C is a type passed to all check functions to provide context.
 type C struct {
 	Filename  string
-	Includes  []string
+	Dirs      []string
 	Program   *ast.Program
 	Check     string
 	Messages  Messages
@@ -204,15 +204,15 @@ func (c *C) Errorf(node ast.Node, message string, args ...interface{}) {
 
 // Resolve resolves a type reference.
 func (c *C) Resolve(ref ast.TypeReference) ast.Node {
-	if n, err := Resolve(ref, c.Program, c.Includes); err == nil {
+	if n, err := Resolve(ref, c.Program, c.Dirs); err == nil {
 		return n
 	}
 	return nil
 }
 
 // ResolveType resolves a type reference to its target type.
 func (c *C) ResolveType(ref ast.TypeReference) ast.Node {
-	if n, err := ResolveType(ref, c.Program, c.Includes); err == nil {
+	if n, err := ResolveType(ref, c.Program, c.Dirs); err == nil {
 		return n
 	}
 	return nil

checks/includes.go

@@ -36,14 +36,8 @@ func CheckIncludePath() *thriftcheck.Check {
 			return
 		}
 
-		// Check the current directory first to match `thrift`s behavior.
-		dirs := c.Includes
-		if cwd, err := os.Getwd(); err != nil {
-			dirs = append([]string{cwd}, c.Includes...)
-		}
-
 		found := false
-		for _, dir := range dirs {
+		for _, dir := range c.Dirs {
 			if _, err := os.Stat(filepath.Join(dir, i.Path)); err == nil {
 				found = true
 				break

linter.go

@@ -21,6 +21,7 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"go.uber.org/thriftrw/ast"
@@ -115,7 +116,7 @@ func (l *Linter) lint(program *ast.Program, filename string, parseInfo *idl.Info
 
 	ctx := &C{
 		Filename:  filename,
-		Includes:  l.includes,
+		Dirs:      append([]string{filepath.Dir(filename)}, l.includes...),
 		Program:   program,
 		logger:    l.logger,
 		parseInfo: parseInfo,

parse.go

@@ -47,11 +47,6 @@ func ParseFile(filename string, dirs []string) (*ast.Program, *idl.Info, error)
 		return nil, nil, fmt.Errorf("%s not found", filename)
 	}
 
-	// Check the current directory first to match `thrift`s behavior.
-	if cwd, err := os.Getwd(); err != nil {
-		dirs = append([]string{cwd}, dirs...)
-	}
-
 	for _, dir := range dirs {
 		if f, err := os.Open(filepath.Join(dir, filename)); err == nil {
 			return Parse(f)