Documentation
¶
Overview ¶
Background
Analyzer
Pass
Modular analysis with Facts
Testing an Analyzer
Standalone commands
Package analysis defines the interface between a modular static
analysis and an analysis driver program.
Background ¶
A static analysis is a function that inspects a package of Go code and
reports a set of diagnostics (typically mistakes in the code), and
perhaps produces other results as well, such as suggested refactorings
or other facts. An analysis that reports mistakes is informally called a
"checker". For example, the printf checker reports mistakes in
fmt.Printf format strings.
A "modular" analysis is one that inspects one package at a time but can
save information from a lower-level package and use it when inspecting a
higher-level package, analogous to separate compilation in a toolchain.
The printf checker is modular: when it discovers that a function such as
log.Fatalf delegates to fmt.Printf, it records this fact, and checks
calls to that function too, including calls made from another package.
By implementing a common interface, checkers from a variety of sources
can be easily selected, incorporated, and reused in a wide range of
driver programs including command-line tools (such as vet), text editors and
IDEs, build and test systems (such as go build, Bazel, or Buck), test
frameworks, code review tools, code-base indexers (such as SourceGraph),
documentation viewers (such as godoc), batch pipelines for large code
bases, and so on.
Analyzer ¶
The primary type in the API is Analyzer. An Analyzer statically
describes an analysis function: its name, documentation, flags,
relationship to other analyzers, and of course, its logic.
To define an analysis, a user declares a (logically constant) variable
of type Analyzer. Here is a typical example from one of the analyzers in
the go/analysis/passes/ subdirectory:
An analysis driver is a program such as vet that runs a set of
analyses and prints the diagnostics that they report.
The driver program must import the list of Analyzers it needs.
Typically each Analyzer resides in a separate package.
To add a new Analyzer to an existing driver, add another item to the list:
A driver may use the name, flags, and documentation to provide on-line
help that describes the analyses it performs.
The doc comment contains a brief one-line summary,
optionally followed by paragraphs of explanation.
The Analyzer type has more fields besides those shown above:
The Flags field declares a set of named (global) flag variables that
control analysis behavior. Unlike vet, analysis flags are not declared
directly in the command line FlagSet; it is up to the driver to set the
flag variables. A driver for a single analysis, a, might expose its flag
f directly on the command line as -f, whereas a driver for multiple
analyses might prefix the flag name by the analysis name (-a.f) to avoid
ambiguity. An IDE might expose the flags through a graphical interface,
and a batch pipeline might configure them from a config file.
See the "findcall" analyzer for an example of flags in action.
The RunDespiteErrors flag indicates whether the analysis is equipped to
handle ill-typed code. If not, the driver will skip the analysis if
there were parse or type errors.
The optional ResultType field specifies the type of the result value
computed by this analysis and made available to other analyses.
The Requires field specifies a list of analyses upon which
this one depends and whose results it may access, and it constrains the
order in which a driver may run analyses.
The FactTypes field is discussed in the section on Modularity.
The analysis package provides a Validate function to perform basic
sanity checks on an Analyzer, such as that its Requires graph is
acyclic, its fact and result types are unique, and so on.
Finally, the Run field contains a function to be called by the driver to
execute the analysis on a single package. The driver passes it an
instance of the Pass type.
Pass ¶
A Pass describes a single unit of work: the application of a particular
Analyzer to a particular package of Go code.
The Pass provides information to the Analyzer's Run function about the
package being analyzed, and provides operations to the Run function for
reporting diagnostics and other information back to the driver.
The Fset, Files, Pkg, and TypesInfo fields provide the syntax trees,
type information, and source positions for a single package of Go code.
The OtherFiles field provides the names of non-Go
files such as assembly that are part of this package.
Similarly, the IgnoredFiles field provides the names of Go and non-Go
source files that are not part of this package with the current build
configuration but may be part of other build configurations.
The contents of these files may be read using Pass.ReadFile;
see the "asmdecl" or "buildtags" analyzers for examples of loading
non-Go files and reporting diagnostics against them.
The ResultOf field provides the results computed by the analyzers
required by this one, as expressed in its Analyzer.Requires field. The
driver runs the required analyzers first and makes their results
available in this map. Each Analyzer must return a value of the type
described in its Analyzer.ResultType field.
For example, the "ctrlflow" analyzer returns a *ctrlflow.CFGs, which
provides a control-flow graph for each function in the package (see
golang.org/x/tools/go/cfg); the "inspect" analyzer returns a value that
enables other Analyzers to traverse the syntax trees of the package more
efficiently; and the "buildssa" analyzer constructs an SSA-form
intermediate representation.
Each of these Analyzers extends the capabilities of later Analyzers
without adding a dependency to the core API, so an analysis tool pays
only for the extensions it needs.
The Report function emits a diagnostic, a message associated with a
source position. For most analyses, diagnostics are their primary
result.
For convenience, Pass provides a helper method, Reportf, to report a new
diagnostic by formatting a string.
Diagnostic is defined as:
The optional Category field is a short identifier that classifies the
kind of message when an analysis produces several kinds of diagnostic.
The Diagnostic struct does not have a field to indicate its severity
because opinions about the relative importance of Analyzers and their
diagnostics vary widely among users. The design of this framework does
not hold each Analyzer responsible for identifying the severity of its
diagnostics. Instead, we expect that drivers will allow the user to
customize the filtering and prioritization of diagnostics based on the
producing Analyzer and optional Category, according to the user's
preferences.
Most Analyzers inspect typed Go syntax trees, but a few, such as asmdecl
and buildtag, inspect the raw text of Go source files or even non-Go
files such as assembly. To report a diagnostic against a line of a
raw text file, use the following sequence:
Modular analysis with Facts ¶
To improve efficiency and scalability, large programs are routinely
built using separate compilation: units of the program are compiled
separately, and recompiled only when one of their dependencies changes;
independent modules may be compiled in parallel. The same technique may
be applied to static analyses, for the same benefits. Such analyses are
described as "modular".
A compiler’s type checker is an example of a modular static analysis.
Many other checkers we would like to apply to Go programs can be
understood as alternative or non-standard type systems. For example,
vet's printf checker infers whether a function has the "printf wrapper"
type, and it applies stricter checks to calls of such functions. In
addition, it records which functions are printf wrappers for use by
later analysis passes to identify other printf wrappers by induction.
A result such as “f is a printf wrapper” that is not interesting by
itself but serves as a stepping stone to an interesting result (such as
a diagnostic) is called a Fact.
The analysis API allows an analysis to define new types of facts, to
associate facts of these types with objects (named entities) declared
within the current package, or with the package as a whole, and to query
for an existing fact of a given type associated with an object or
package.
An Analyzer that uses facts must declare their types:
The driver program ensures that facts for a pass’s dependencies are
generated before analyzing the package and is responsible for propagating
facts from one package to another, possibly across address spaces.
Consequently, Facts must be serializable. The API requires that drivers
use the gob encoding, an efficient, robust, self-describing binary
protocol. A fact type may implement the GobEncoder/GobDecoder interfaces
if the default encoding is unsuitable. Facts should be stateless.
Because serialized facts may appear within build outputs, the gob encoding
of a fact must be deterministic, to avoid spurious cache misses in
build systems that use content-addressable caches.
The driver makes a single call to the gob encoder for all facts
exported by a given analysis pass, so that the topology of
shared data structures referenced by multiple facts is preserved.
The Pass type has functions to import and export facts,
associated either with an object or with a package:
An Analyzer may only export facts associated with the current package or
its objects, though it may import facts from any package or object that
is an import dependency of the current package.
Conceptually, ExportObjectFact(obj, fact) inserts fact into a hidden map keyed by
the pair (obj, TypeOf(fact)), and the ImportObjectFact function
retrieves the entry from this map and copies its value into the variable
pointed to by fact. This scheme assumes that the concrete type of fact
is a pointer; this assumption is checked by the Validate function.
See the "printf" analyzer for an example of object facts in action.
Some driver implementations (such as those based on Bazel and Blaze) do
not currently apply analyzers to packages of the standard library.
Therefore, for best results, analyzer authors should not rely on
analysis facts being available for standard packages.
For example, although the printf checker is capable of deducing during
analysis of the log package that log.Printf is a printf wrapper,
this fact is built in to the analyzer so that it correctly checks
calls to log.Printf even when run in a driver that does not apply
it to standard packages. We would like to remove this limitation in future.
Testing an Analyzer ¶
The analysistest subpackage provides utilities for testing an Analyzer.
In a few lines of code, it is possible to run an analyzer on a package
of testdata files and check that it reported all the expected
diagnostics and facts (and no more). Expectations are expressed using
"// want ..." comments in the input code.
Standalone commands ¶
Analyzers are provided in the form of packages that a driver program is
expected to import. The vet command imports a set of several analyzers,
but users may wish to define their own analysis commands that perform
additional checks. To simplify the task of creating an analysis command,
either for a single analyzer or for a whole suite, we provide the
singlechecker and multichecker subpackages.
The singlechecker package provides the main function for a command that
runs one analyzer. By convention, each analyzer such as
go/analysis/passes/findcall should be accompanied by a singlechecker-based
command such as go/analysis/passes/findcall/cmd/findcall, defined in its
entirety as:
A tool that provides multiple analyzers can use multichecker in a
similar way, giving it the list of Analyzers.
Index ¶
func Validate(analyzers []*Analyzer) error
[func Validate(analyzers []*Analyzer) error](#Validate)
type Analyzer
func (a *Analyzer) String() string
func (a *Analyzer) String() string
func (a *Analyzer) String() string
type CycleInRequiresGraphError
type CycleInRequiresGraphError
func (e *CycleInRequiresGraphError) Error() string
func (e *CycleInRequiresGraphError) Error() string
func (e *CycleInRequiresGraphError) Error() string
type Diagnostic
type Fact
type Module
type ModuleError
type ObjectFact
type PackageFact
type Pass
func (pass *Pass) ReportRangef(rng Range, format string, args ...any)
func (pass *Pass) Reportf(pos token.Pos, format string, args ...any)
func (pass *Pass) String() string
func (pass *Pass) ReportRangef(rng Range, format string, args ...any)
func (pass *Pass) ReportRangef(rng Range, format string, args ...any)
func (pass *Pass) Reportf(pos token.Pos, format string, args ...any)
func (pass *Pass) Reportf(pos token.Pos, format string, args ...any)
func (pass *Pass) String() string
func (pass *Pass) String() string
type Range
type RelatedInformation
type SuggestedFix
type TextEdit
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func Validate ¶
Validate reports an error if any of the analyzers are misconfigured.
Checks include:
that the name is a valid identifier;
that the Doc is not empty;
that the Run is non-nil;
that the Requires graph is acyclic;
that analyzer fact types are unique;
that each fact type is a pointer.
Analyzer names need not be unique, though this may be confusing.
Types ¶
type Analyzer ¶
An Analyzer describes an analysis function and its options.
func (*Analyzer) String ¶
type CycleInRequiresGraphError ¶
func (*CycleInRequiresGraphError) Error ¶
type Diagnostic ¶
https://pkg.go.dev/net/url#URL.ResolveReference
A Diagnostic is a message associated with a source location or range.
An Analyzer may return a variety of diagnostics; the optional Category,
which should be a constant, may be used to classify them.
It is primarily intended to make it easy to look up documentation.
All Pos values are interpreted relative to Pass.Fset. If End is
provided, the diagnostic is specified to apply to the range between
Pos and End.
type Fact ¶
A Fact is an intermediate fact produced during analysis.
Each fact is associated with a named declaration (a types.Object) or
with a package as a whole. A single object or package may have
multiple associated facts, but only one of any particular fact type.
A Fact represents a predicate such as "never returns", but does not
represent the subject of the predicate such as "function F" or "package P".
Facts may be produced in one analysis pass and consumed by another
analysis pass even if these are in different address spaces.
If package P imports Q, all facts about Q produced during
analysis of that package will be available during later analysis of P.
Facts are analogous to type export data in a build system:
just as export data enables separate compilation of several passes,
facts enable "separate analysis".
Each pass (a, p) starts with the set of facts produced by the
same analyzer a applied to the packages directly imported by p.
The analysis may add facts to the set, and they may be exported in turn.
An analysis's Run function may retrieve facts by calling
Pass.Import{Object,Package}Fact and update them using
Pass.Export{Object,Package}Fact.
A fact is logically private to its Analysis. To pass values
between different analyzers, use the results mechanism;
see Analyzer.Requires, Analyzer.ResultType, and Pass.ResultOf.
A Fact type must be a pointer.
Facts are encoded and decoded using encoding/gob.
A Fact may implement the GobEncoder/GobDecoder interfaces
to customize its encoding. Fact encoding should not fail.
A Fact should not be modified once exported.
type Module ¶
added in
v0.24.0
A Module describes the module to which a package belongs.
type ModuleError ¶
added in
v0.43.0
ModuleError holds errors loading a module.
type ObjectFact ¶
ObjectFact is an object together with an associated fact.
type PackageFact ¶
PackageFact is a package together with an associated fact.
type Pass ¶
A Pass provides information to the Run function that
applies a specific analyzer to a single Go package.
It forms the interface between the analysis logic and the driver
program, and has both input and an output components.
As in a compiler, one pass may depend on the result computed by another.
The Run function should not call any of the Pass functions concurrently.
func (*Pass) ReportRangef ¶
ReportRangef is a helper function that reports a Diagnostic using the
range provided. ast.Node values can be passed in as the range because
they satisfy the Range interface.
func (*Pass) Reportf ¶
Reportf is a helper function that reports a Diagnostic using the
specified position and formatted error message.
func (*Pass) String ¶
type Range ¶
The Range interface provides a range. It's equivalent to and satisfied by
ast.Node.
type RelatedInformation ¶
RelatedInformation contains information related to a diagnostic.
For example, a diagnostic that flags duplicated declarations of a
variable may include one RelatedInformation per existing
declaration.
type SuggestedFix ¶
A SuggestedFix is a code change associated with a Diagnostic that a
user can choose to apply to their code. Usually the SuggestedFix is
meant to fix the issue flagged by the diagnostic.
The TextEdits must not overlap, nor contain edits for other
packages. Edits need not be totally ordered, but the order
determines how insertions at the same point will be applied.
type TextEdit ¶
A TextEdit represents the replacement of the code between Pos and End with the new text.
Each TextEdit should apply to a single file. End should not be earlier in the file than Pos.
Source Files
¶
analysis.go
diagnostic.go
doc.go
validate.go
Directories
¶
fieldalignment/cmd/fieldalignment
reflectvaluecompare/cmd/reflectvaluecompare
stringintconv/cmd/stringintconv