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Diffstat (limited to 'vendor/golang.org/x/tools/go/loader/doc.go')
| -rw-r--r-- | vendor/golang.org/x/tools/go/loader/doc.go | 205 |
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diff --git a/vendor/golang.org/x/tools/go/loader/doc.go b/vendor/golang.org/x/tools/go/loader/doc.go deleted file mode 100644 index 9b51c9e..0000000 --- a/vendor/golang.org/x/tools/go/loader/doc.go +++ /dev/null @@ -1,205 +0,0 @@ -// Copyright 2015 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 file. - -// Package loader loads a complete Go program from source code, parsing -// and type-checking the initial packages plus their transitive closure -// of dependencies. The ASTs and the derived facts are retained for -// later use. -// -// THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE. -// -// The package defines two primary types: Config, which specifies a -// set of initial packages to load and various other options; and -// Program, which is the result of successfully loading the packages -// specified by a configuration. -// -// The configuration can be set directly, but *Config provides various -// convenience methods to simplify the common cases, each of which can -// be called any number of times. Finally, these are followed by a -// call to Load() to actually load and type-check the program. -// -// var conf loader.Config -// -// // Use the command-line arguments to specify -// // a set of initial packages to load from source. -// // See FromArgsUsage for help. -// rest, err := conf.FromArgs(os.Args[1:], wantTests) -// -// // Parse the specified files and create an ad hoc package with path "foo". -// // All files must have the same 'package' declaration. -// conf.CreateFromFilenames("foo", "foo.go", "bar.go") -// -// // Create an ad hoc package with path "foo" from -// // the specified already-parsed files. -// // All ASTs must have the same 'package' declaration. -// conf.CreateFromFiles("foo", parsedFiles) -// -// // Add "runtime" to the set of packages to be loaded. -// conf.Import("runtime") -// -// // Adds "fmt" and "fmt_test" to the set of packages -// // to be loaded. "fmt" will include *_test.go files. -// conf.ImportWithTests("fmt") -// -// // Finally, load all the packages specified by the configuration. -// prog, err := conf.Load() -// -// See examples_test.go for examples of API usage. -// -// -// CONCEPTS AND TERMINOLOGY -// -// The WORKSPACE is the set of packages accessible to the loader. The -// workspace is defined by Config.Build, a *build.Context. The -// default context treats subdirectories of $GOROOT and $GOPATH as -// packages, but this behavior may be overridden. -// -// An AD HOC package is one specified as a set of source files on the -// command line. In the simplest case, it may consist of a single file -// such as $GOROOT/src/net/http/triv.go. -// -// EXTERNAL TEST packages are those comprised of a set of *_test.go -// files all with the same 'package foo_test' declaration, all in the -// same directory. (go/build.Package calls these files XTestFiles.) -// -// An IMPORTABLE package is one that can be referred to by some import -// spec. Every importable package is uniquely identified by its -// PACKAGE PATH or just PATH, a string such as "fmt", "encoding/json", -// or "cmd/vendor/golang.org/x/arch/x86/x86asm". A package path -// typically denotes a subdirectory of the workspace. -// -// An import declaration uses an IMPORT PATH to refer to a package. -// Most import declarations use the package path as the import path. -// -// Due to VENDORING (https://golang.org/s/go15vendor), the -// interpretation of an import path may depend on the directory in which -// it appears. To resolve an import path to a package path, go/build -// must search the enclosing directories for a subdirectory named -// "vendor". -// -// ad hoc packages and external test packages are NON-IMPORTABLE. The -// path of an ad hoc package is inferred from the package -// declarations of its files and is therefore not a unique package key. -// For example, Config.CreatePkgs may specify two initial ad hoc -// packages, both with path "main". -// -// An AUGMENTED package is an importable package P plus all the -// *_test.go files with same 'package foo' declaration as P. -// (go/build.Package calls these files TestFiles.) -// -// The INITIAL packages are those specified in the configuration. A -// DEPENDENCY is a package loaded to satisfy an import in an initial -// package or another dependency. -// -package loader - -// IMPLEMENTATION NOTES -// -// 'go test', in-package test files, and import cycles -// --------------------------------------------------- -// -// An external test package may depend upon members of the augmented -// package that are not in the unaugmented package, such as functions -// that expose internals. (See bufio/export_test.go for an example.) -// So, the loader must ensure that for each external test package -// it loads, it also augments the corresponding non-test package. -// -// The import graph over n unaugmented packages must be acyclic; the -// import graph over n-1 unaugmented packages plus one augmented -// package must also be acyclic. ('go test' relies on this.) But the -// import graph over n augmented packages may contain cycles. -// -// First, all the (unaugmented) non-test packages and their -// dependencies are imported in the usual way; the loader reports an -// error if it detects an import cycle. -// -// Then, each package P for which testing is desired is augmented by -// the list P' of its in-package test files, by calling -// (*types.Checker).Files. This arrangement ensures that P' may -// reference definitions within P, but P may not reference definitions -// within P'. Furthermore, P' may import any other package, including -// ones that depend upon P, without an import cycle error. -// -// Consider two packages A and B, both of which have lists of -// in-package test files we'll call A' and B', and which have the -// following import graph edges: -// B imports A -// B' imports A -// A' imports B -// This last edge would be expected to create an error were it not -// for the special type-checking discipline above. -// Cycles of size greater than two are possible. For example: -// compress/bzip2/bzip2_test.go (package bzip2) imports "io/ioutil" -// io/ioutil/tempfile_test.go (package ioutil) imports "regexp" -// regexp/exec_test.go (package regexp) imports "compress/bzip2" -// -// -// Concurrency -// ----------- -// -// Let us define the import dependency graph as follows. Each node is a -// list of files passed to (Checker).Files at once. Many of these lists -// are the production code of an importable Go package, so those nodes -// are labelled by the package's path. The remaining nodes are -// ad hoc packages and lists of in-package *_test.go files that augment -// an importable package; those nodes have no label. -// -// The edges of the graph represent import statements appearing within a -// file. An edge connects a node (a list of files) to the node it -// imports, which is importable and thus always labelled. -// -// Loading is controlled by this dependency graph. -// -// To reduce I/O latency, we start loading a package's dependencies -// asynchronously as soon as we've parsed its files and enumerated its -// imports (scanImports). This performs a preorder traversal of the -// import dependency graph. -// -// To exploit hardware parallelism, we type-check unrelated packages in -// parallel, where "unrelated" means not ordered by the partial order of -// the import dependency graph. -// -// We use a concurrency-safe non-blocking cache (importer.imported) to -// record the results of type-checking, whether success or failure. An -// entry is created in this cache by startLoad the first time the -// package is imported. The first goroutine to request an entry becomes -// responsible for completing the task and broadcasting completion to -// subsequent requestors, which block until then. -// -// Type checking occurs in (parallel) postorder: we cannot type-check a -// set of files until we have loaded and type-checked all of their -// immediate dependencies (and thus all of their transitive -// dependencies). If the input were guaranteed free of import cycles, -// this would be trivial: we could simply wait for completion of the -// dependencies and then invoke the typechecker. -// -// But as we saw in the 'go test' section above, some cycles in the -// import graph over packages are actually legal, so long as the -// cycle-forming edge originates in the in-package test files that -// augment the package. This explains why the nodes of the import -// dependency graph are not packages, but lists of files: the unlabelled -// nodes avoid the cycles. Consider packages A and B where B imports A -// and A's in-package tests AT import B. The naively constructed import -// graph over packages would contain a cycle (A+AT) --> B --> (A+AT) but -// the graph over lists of files is AT --> B --> A, where AT is an -// unlabelled node. -// -// Awaiting completion of the dependencies in a cyclic graph would -// deadlock, so we must materialize the import dependency graph (as -// importer.graph) and check whether each import edge forms a cycle. If -// x imports y, and the graph already contains a path from y to x, then -// there is an import cycle, in which case the processing of x must not -// wait for the completion of processing of y. -// -// When the type-checker makes a callback (doImport) to the loader for a -// given import edge, there are two possible cases. In the normal case, -// the dependency has already been completely type-checked; doImport -// does a cache lookup and returns it. In the cyclic case, the entry in -// the cache is still necessarily incomplete, indicating a cycle. We -// perform the cycle check again to obtain the error message, and return -// the error. -// -// The result of using concurrency is about a 2.5x speedup for stdlib_test. - -// TODO(adonovan): overhaul the package documentation. |