1 // Copyright 2018 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 /* 6 Package packages loads Go packages for inspection and analysis. 7 8 The Load function takes as input a list of patterns and return a list of Package 9 structs describing individual packages matched by those patterns. 10 The LoadMode controls the amount of detail in the loaded packages. 11 12 Load passes most patterns directly to the underlying build tool, 13 but all patterns with the prefix "query=", where query is a 14 non-empty string of letters from [a-z], are reserved and may be 15 interpreted as query operators. 16 17 Two query operators are currently supported: "file" and "pattern". 18 19 The query "file=path/to/file.go" matches the package or packages enclosing 20 the Go source file path/to/file.go. For example "file=~/go/src/fmt/print.go" 21 might return the packages "fmt" and "fmt [fmt.test]". 22 23 The query "pattern=string" causes "string" to be passed directly to 24 the underlying build tool. In most cases this is unnecessary, 25 but an application can use Load("pattern=" + x) as an escaping mechanism 26 to ensure that x is not interpreted as a query operator if it contains '='. 27 28 All other query operators are reserved for future use and currently 29 cause Load to report an error. 30 31 The Package struct provides basic information about the package, including 32 33 - ID, a unique identifier for the package in the returned set; 34 - GoFiles, the names of the package's Go source files; 35 - Imports, a map from source import strings to the Packages they name; 36 - Types, the type information for the package's exported symbols; 37 - Syntax, the parsed syntax trees for the package's source code; and 38 - TypeInfo, the result of a complete type-check of the package syntax trees. 39 40 (See the documentation for type Package for the complete list of fields 41 and more detailed descriptions.) 42 43 For example, 44 45 Load(nil, "bytes", "unicode...") 46 47 returns four Package structs describing the standard library packages 48 bytes, unicode, unicode/utf16, and unicode/utf8. Note that one pattern 49 can match multiple packages and that a package might be matched by 50 multiple patterns: in general it is not possible to determine which 51 packages correspond to which patterns. 52 53 Note that the list returned by Load contains only the packages matched 54 by the patterns. Their dependencies can be found by walking the import 55 graph using the Imports fields. 56 57 The Load function can be configured by passing a pointer to a Config as 58 the first argument. A nil Config is equivalent to the zero Config, which 59 causes Load to run in LoadFiles mode, collecting minimal information. 60 See the documentation for type Config for details. 61 62 As noted earlier, the Config.Mode controls the amount of detail 63 reported about the loaded packages. See the documentation for type LoadMode 64 for details. 65 66 Most tools should pass their command-line arguments (after any flags) 67 uninterpreted to the loader, so that the loader can interpret them 68 according to the conventions of the underlying build system. 69 See the Example function for typical usage. 70 */ 71 package packages // import "golang.org/x/tools/go/packages" 72 73 /* 74 75 Motivation and design considerations 76 77 The new package's design solves problems addressed by two existing 78 packages: go/build, which locates and describes packages, and 79 golang.org/x/tools/go/loader, which loads, parses and type-checks them. 80 The go/build.Package structure encodes too much of the 'go build' way 81 of organizing projects, leaving us in need of a data type that describes a 82 package of Go source code independent of the underlying build system. 83 We wanted something that works equally well with go build and vgo, and 84 also other build systems such as Bazel and Blaze, making it possible to 85 construct analysis tools that work in all these environments. 86 Tools such as errcheck and staticcheck were essentially unavailable to 87 the Go community at Google, and some of Google's internal tools for Go 88 are unavailable externally. 89 This new package provides a uniform way to obtain package metadata by 90 querying each of these build systems, optionally supporting their 91 preferred command-line notations for packages, so that tools integrate 92 neatly with users' build environments. The Metadata query function 93 executes an external query tool appropriate to the current workspace. 94 95 Loading packages always returns the complete import graph "all the way down", 96 even if all you want is information about a single package, because the query 97 mechanisms of all the build systems we currently support ({go,vgo} list, and 98 blaze/bazel aspect-based query) cannot provide detailed information 99 about one package without visiting all its dependencies too, so there is 100 no additional asymptotic cost to providing transitive information. 101 (This property might not be true of a hypothetical 5th build system.) 102 103 In calls to TypeCheck, all initial packages, and any package that 104 transitively depends on one of them, must be loaded from source. 105 Consider A->B->C->D->E: if A,C are initial, A,B,C must be loaded from 106 source; D may be loaded from export data, and E may not be loaded at all 107 (though it's possible that D's export data mentions it, so a 108 types.Package may be created for it and exposed.) 109 110 The old loader had a feature to suppress type-checking of function 111 bodies on a per-package basis, primarily intended to reduce the work of 112 obtaining type information for imported packages. Now that imports are 113 satisfied by export data, the optimization no longer seems necessary. 114 115 Despite some early attempts, the old loader did not exploit export data, 116 instead always using the equivalent of WholeProgram mode. This was due 117 to the complexity of mixing source and export data packages (now 118 resolved by the upward traversal mentioned above), and because export data 119 files were nearly always missing or stale. Now that 'go build' supports 120 caching, all the underlying build systems can guarantee to produce 121 export data in a reasonable (amortized) time. 122 123 Test "main" packages synthesized by the build system are now reported as 124 first-class packages, avoiding the need for clients (such as go/ssa) to 125 reinvent this generation logic. 126 127 One way in which go/packages is simpler than the old loader is in its 128 treatment of in-package tests. In-package tests are packages that 129 consist of all the files of the library under test, plus the test files. 130 The old loader constructed in-package tests by a two-phase process of 131 mutation called "augmentation": first it would construct and type check 132 all the ordinary library packages and type-check the packages that 133 depend on them; then it would add more (test) files to the package and 134 type-check again. This two-phase approach had four major problems: 135 1) in processing the tests, the loader modified the library package, 136 leaving no way for a client application to see both the test 137 package and the library package; one would mutate into the other. 138 2) because test files can declare additional methods on types defined in 139 the library portion of the package, the dispatch of method calls in 140 the library portion was affected by the presence of the test files. 141 This should have been a clue that the packages were logically 142 different. 143 3) this model of "augmentation" assumed at most one in-package test 144 per library package, which is true of projects using 'go build', 145 but not other build systems. 146 4) because of the two-phase nature of test processing, all packages that 147 import the library package had to be processed before augmentation, 148 forcing a "one-shot" API and preventing the client from calling Load 149 in several times in sequence as is now possible in WholeProgram mode. 150 (TypeCheck mode has a similar one-shot restriction for a different reason.) 151 152 Early drafts of this package supported "multi-shot" operation. 153 Although it allowed clients to make a sequence of calls (or concurrent 154 calls) to Load, building up the graph of Packages incrementally, 155 it was of marginal value: it complicated the API 156 (since it allowed some options to vary across calls but not others), 157 it complicated the implementation, 158 it cannot be made to work in Types mode, as explained above, 159 and it was less efficient than making one combined call (when this is possible). 160 Among the clients we have inspected, none made multiple calls to load 161 but could not be easily and satisfactorily modified to make only a single call. 162 However, applications changes may be required. 163 For example, the ssadump command loads the user-specified packages 164 and in addition the runtime package. It is tempting to simply append 165 "runtime" to the user-provided list, but that does not work if the user 166 specified an ad-hoc package such as [a.go b.go]. 167 Instead, ssadump no longer requests the runtime package, 168 but seeks it among the dependencies of the user-specified packages, 169 and emits an error if it is not found. 170 171 Overlays: The Overlay field in the Config allows providing alternate contents 172 for Go source files, by providing a mapping from file path to contents. 173 go/packages will pull in new imports added in overlay files when go/packages 174 is run in LoadImports mode or greater. 175 Overlay support for the go list driver isn't complete yet: if the file doesn't 176 exist on disk, it will only be recognized in an overlay if it is a non-test file 177 and the package would be reported even without the overlay. 178 179 Questions & Tasks 180 181 - Add GOARCH/GOOS? 182 They are not portable concepts, but could be made portable. 183 Our goal has been to allow users to express themselves using the conventions 184 of the underlying build system: if the build system honors GOARCH 185 during a build and during a metadata query, then so should 186 applications built atop that query mechanism. 187 Conversely, if the target architecture of the build is determined by 188 command-line flags, the application can pass the relevant 189 flags through to the build system using a command such as: 190 myapp -query_flag="--cpu=amd64" -query_flag="--os=darwin" 191 However, this approach is low-level, unwieldy, and non-portable. 192 GOOS and GOARCH seem important enough to warrant a dedicated option. 193 194 - How should we handle partial failures such as a mixture of good and 195 malformed patterns, existing and non-existent packages, successful and 196 failed builds, import failures, import cycles, and so on, in a call to 197 Load? 198 199 - Support bazel, blaze, and go1.10 list, not just go1.11 list. 200 201 - Handle (and test) various partial success cases, e.g. 202 a mixture of good packages and: 203 invalid patterns 204 nonexistent packages 205 empty packages 206 packages with malformed package or import declarations 207 unreadable files 208 import cycles 209 other parse errors 210 type errors 211 Make sure we record errors at the correct place in the graph. 212 213 - Missing packages among initial arguments are not reported. 214 Return bogus packages for them, like golist does. 215 216 - "undeclared name" errors (for example) are reported out of source file 217 order. I suspect this is due to the breadth-first resolution now used 218 by go/types. Is that a bug? Discuss with gri. 219 220 */ 221