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Source file src/go/internal/srcimporter/srcimporter.go

Documentation: go/internal/srcimporter

     1  // Copyright 2017 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package srcimporter implements importing directly
     6  // from source files rather than installed packages.
     7  package srcimporter // import "go/internal/srcimporter"
     8  
     9  import (
    10  	"fmt"
    11  	"go/ast"
    12  	"go/build"
    13  	"go/parser"
    14  	"go/token"
    15  	"go/types"
    16  	"io"
    17  	"os"
    18  	"path/filepath"
    19  	"sync"
    20  )
    21  
    22  // An Importer provides the context for importing packages from source code.
    23  type Importer struct {
    24  	ctxt     *build.Context
    25  	fset     *token.FileSet
    26  	sizes    types.Sizes
    27  	packages map[string]*types.Package
    28  }
    29  
    30  // NewImporter returns a new Importer for the given context, file set, and map
    31  // of packages. The context is used to resolve import paths to package paths,
    32  // and identifying the files belonging to the package. If the context provides
    33  // non-nil file system functions, they are used instead of the regular package
    34  // os functions. The file set is used to track position information of package
    35  // files; and imported packages are added to the packages map.
    36  func New(ctxt *build.Context, fset *token.FileSet, packages map[string]*types.Package) *Importer {
    37  	return &Importer{
    38  		ctxt:     ctxt,
    39  		fset:     fset,
    40  		sizes:    types.SizesFor(ctxt.Compiler, ctxt.GOARCH), // uses go/types default if GOARCH not found
    41  		packages: packages,
    42  	}
    43  }
    44  
    45  // Importing is a sentinel taking the place in Importer.packages
    46  // for a package that is in the process of being imported.
    47  var importing types.Package
    48  
    49  // Import(path) is a shortcut for ImportFrom(path, ".", 0).
    50  func (p *Importer) Import(path string) (*types.Package, error) {
    51  	return p.ImportFrom(path, ".", 0) // use "." rather than "" (see issue #24441)
    52  }
    53  
    54  // ImportFrom imports the package with the given import path resolved from the given srcDir,
    55  // adds the new package to the set of packages maintained by the importer, and returns the
    56  // package. Package path resolution and file system operations are controlled by the context
    57  // maintained with the importer. The import mode must be zero but is otherwise ignored.
    58  // Packages that are not comprised entirely of pure Go files may fail to import because the
    59  // type checker may not be able to determine all exported entities (e.g. due to cgo dependencies).
    60  func (p *Importer) ImportFrom(path, srcDir string, mode types.ImportMode) (*types.Package, error) {
    61  	if mode != 0 {
    62  		panic("non-zero import mode")
    63  	}
    64  
    65  	if abs, err := p.absPath(srcDir); err == nil { // see issue #14282
    66  		srcDir = abs
    67  	}
    68  	bp, err := p.ctxt.Import(path, srcDir, 0)
    69  	if err != nil {
    70  		return nil, err // err may be *build.NoGoError - return as is
    71  	}
    72  
    73  	// package unsafe is known to the type checker
    74  	if bp.ImportPath == "unsafe" {
    75  		return types.Unsafe, nil
    76  	}
    77  
    78  	// no need to re-import if the package was imported completely before
    79  	pkg := p.packages[bp.ImportPath]
    80  	if pkg != nil {
    81  		if pkg == &importing {
    82  			return nil, fmt.Errorf("import cycle through package %q", bp.ImportPath)
    83  		}
    84  		if !pkg.Complete() {
    85  			// Package exists but is not complete - we cannot handle this
    86  			// at the moment since the source importer replaces the package
    87  			// wholesale rather than augmenting it (see #19337 for details).
    88  			// Return incomplete package with error (see #16088).
    89  			return pkg, fmt.Errorf("reimported partially imported package %q", bp.ImportPath)
    90  		}
    91  		return pkg, nil
    92  	}
    93  
    94  	p.packages[bp.ImportPath] = &importing
    95  	defer func() {
    96  		// clean up in case of error
    97  		// TODO(gri) Eventually we may want to leave a (possibly empty)
    98  		// package in the map in all cases (and use that package to
    99  		// identify cycles). See also issue 16088.
   100  		if p.packages[bp.ImportPath] == &importing {
   101  			p.packages[bp.ImportPath] = nil
   102  		}
   103  	}()
   104  
   105  	var filenames []string
   106  	filenames = append(filenames, bp.GoFiles...)
   107  	filenames = append(filenames, bp.CgoFiles...)
   108  
   109  	files, err := p.parseFiles(bp.Dir, filenames)
   110  	if err != nil {
   111  		return nil, err
   112  	}
   113  
   114  	// type-check package files
   115  	var firstHardErr error
   116  	conf := types.Config{
   117  		IgnoreFuncBodies: true,
   118  		FakeImportC:      true,
   119  		// continue type-checking after the first error
   120  		Error: func(err error) {
   121  			if firstHardErr == nil && !err.(types.Error).Soft {
   122  				firstHardErr = err
   123  			}
   124  		},
   125  		Importer: p,
   126  		Sizes:    p.sizes,
   127  	}
   128  	pkg, err = conf.Check(bp.ImportPath, p.fset, files, nil)
   129  	if err != nil {
   130  		// If there was a hard error it is possibly unsafe
   131  		// to use the package as it may not be fully populated.
   132  		// Do not return it (see also #20837, #20855).
   133  		if firstHardErr != nil {
   134  			pkg = nil
   135  			err = firstHardErr // give preference to first hard error over any soft error
   136  		}
   137  		return pkg, fmt.Errorf("type-checking package %q failed (%v)", bp.ImportPath, err)
   138  	}
   139  	if firstHardErr != nil {
   140  		// this can only happen if we have a bug in go/types
   141  		panic("package is not safe yet no error was returned")
   142  	}
   143  
   144  	p.packages[bp.ImportPath] = pkg
   145  	return pkg, nil
   146  }
   147  
   148  func (p *Importer) parseFiles(dir string, filenames []string) ([]*ast.File, error) {
   149  	// use build.Context's OpenFile if there is one
   150  	open := p.ctxt.OpenFile
   151  	if open == nil {
   152  		open = func(name string) (io.ReadCloser, error) { return os.Open(name) }
   153  	}
   154  
   155  	files := make([]*ast.File, len(filenames))
   156  	errors := make([]error, len(filenames))
   157  
   158  	var wg sync.WaitGroup
   159  	wg.Add(len(filenames))
   160  	for i, filename := range filenames {
   161  		go func(i int, filepath string) {
   162  			defer wg.Done()
   163  			src, err := open(filepath)
   164  			if err != nil {
   165  				errors[i] = err // open provides operation and filename in error
   166  				return
   167  			}
   168  			files[i], errors[i] = parser.ParseFile(p.fset, filepath, src, 0)
   169  			src.Close() // ignore Close error - parsing may have succeeded which is all we need
   170  		}(i, p.joinPath(dir, filename))
   171  	}
   172  	wg.Wait()
   173  
   174  	// if there are errors, return the first one for deterministic results
   175  	for _, err := range errors {
   176  		if err != nil {
   177  			return nil, err
   178  		}
   179  	}
   180  
   181  	return files, nil
   182  }
   183  
   184  // context-controlled file system operations
   185  
   186  func (p *Importer) absPath(path string) (string, error) {
   187  	// TODO(gri) This should be using p.ctxt.AbsPath which doesn't
   188  	// exist but probably should. See also issue #14282.
   189  	return filepath.Abs(path)
   190  }
   191  
   192  func (p *Importer) isAbsPath(path string) bool {
   193  	if f := p.ctxt.IsAbsPath; f != nil {
   194  		return f(path)
   195  	}
   196  	return filepath.IsAbs(path)
   197  }
   198  
   199  func (p *Importer) joinPath(elem ...string) string {
   200  	if f := p.ctxt.JoinPath; f != nil {
   201  		return f(elem...)
   202  	}
   203  	return filepath.Join(elem...)
   204  }
   205  

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