Giant blob of minor changes

[dotfiles/.git] / .config / coc / extensions / coc-go-data / tools / pkg / mod / golang.org / x / tools@v0.0.0-20201028153306-37f0764111ff / go / ssa / source.go

// Copyright 2013 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 ssa

// This file defines utilities for working with source positions
// or source-level named entities ("objects").

// TODO(adonovan): test that {Value,Instruction}.Pos() positions match
// the originating syntax, as specified.

import (
        "go/ast"
        "go/token"
        "go/types"
)

// EnclosingFunction returns the function that contains the syntax
// node denoted by path.
//
// Syntax associated with package-level variable specifications is
// enclosed by the package's init() function.
//
// Returns nil if not found; reasons might include:
//    - the node is not enclosed by any function.
//    - the node is within an anonymous function (FuncLit) and
//      its SSA function has not been created yet
//      (pkg.Build() has not yet been called).
//
func EnclosingFunction(pkg *Package, path []ast.Node) *Function {
        // Start with package-level function...
        fn := findEnclosingPackageLevelFunction(pkg, path)
        if fn == nil {
                return nil // not in any function
        }

        // ...then walk down the nested anonymous functions.
        n := len(path)
outer:
        for i := range path {
                if lit, ok := path[n-1-i].(*ast.FuncLit); ok {
                        for _, anon := range fn.AnonFuncs {
                                if anon.Pos() == lit.Type.Func {
                                        fn = anon
                                        continue outer
                                }
                        }
                        // SSA function not found:
                        // - package not yet built, or maybe
                        // - builder skipped FuncLit in dead block
                        //   (in principle; but currently the Builder
                        //   generates even dead FuncLits).
                        return nil
                }
        }
        return fn
}

// HasEnclosingFunction returns true if the AST node denoted by path
// is contained within the declaration of some function or
// package-level variable.
//
// Unlike EnclosingFunction, the behaviour of this function does not
// depend on whether SSA code for pkg has been built, so it can be
// used to quickly reject check inputs that will cause
// EnclosingFunction to fail, prior to SSA building.
//
func HasEnclosingFunction(pkg *Package, path []ast.Node) bool {
        return findEnclosingPackageLevelFunction(pkg, path) != nil
}

// findEnclosingPackageLevelFunction returns the Function
// corresponding to the package-level function enclosing path.
//
func findEnclosingPackageLevelFunction(pkg *Package, path []ast.Node) *Function {
        if n := len(path); n >= 2 { // [... {Gen,Func}Decl File]
                switch decl := path[n-2].(type) {
                case *ast.GenDecl:
                        if decl.Tok == token.VAR && n >= 3 {
                                // Package-level 'var' initializer.
                                return pkg.init
                        }

                case *ast.FuncDecl:
                        if decl.Recv == nil && decl.Name.Name == "init" {
                                // Explicit init() function.
                                for _, b := range pkg.init.Blocks {
                                        for _, instr := range b.Instrs {
                                                if instr, ok := instr.(*Call); ok {
                                                        if callee, ok := instr.Call.Value.(*Function); ok && callee.Pkg == pkg && callee.Pos() == decl.Name.NamePos {
                                                                return callee
                                                        }
                                                }
                                        }
                                }
                                // Hack: return non-nil when SSA is not yet
                                // built so that HasEnclosingFunction works.
                                return pkg.init
                        }
                        // Declared function/method.
                        return findNamedFunc(pkg, decl.Name.NamePos)
                }
        }
        return nil // not in any function
}

// findNamedFunc returns the named function whose FuncDecl.Ident is at
// position pos.
//
func findNamedFunc(pkg *Package, pos token.Pos) *Function {
        // Look at all package members and method sets of named types.
        // Not very efficient.
        for _, mem := range pkg.Members {
                switch mem := mem.(type) {
                case *Function:
                        if mem.Pos() == pos {
                                return mem
                        }
                case *Type:
                        mset := pkg.Prog.MethodSets.MethodSet(types.NewPointer(mem.Type()))
                        for i, n := 0, mset.Len(); i < n; i++ {
                                // Don't call Program.Method: avoid creating wrappers.
                                obj := mset.At(i).Obj().(*types.Func)
                                if obj.Pos() == pos {
                                        return pkg.values[obj].(*Function)
                                }
                        }
                }
        }
        return nil
}

// ValueForExpr returns the SSA Value that corresponds to non-constant
// expression e.
//
// It returns nil if no value was found, e.g.
//    - the expression is not lexically contained within f;
//    - f was not built with debug information; or
//    - e is a constant expression.  (For efficiency, no debug
//      information is stored for constants. Use
//      go/types.Info.Types[e].Value instead.)
//    - e is a reference to nil or a built-in function.
//    - the value was optimised away.
//
// If e is an addressable expression used in an lvalue context,
// value is the address denoted by e, and isAddr is true.
//
// The types of e (or &e, if isAddr) and the result are equal
// (modulo "untyped" bools resulting from comparisons).
//
// (Tip: to find the ssa.Value given a source position, use
// astutil.PathEnclosingInterval to locate the ast.Node, then
// EnclosingFunction to locate the Function, then ValueForExpr to find
// the ssa.Value.)
//
func (f *Function) ValueForExpr(e ast.Expr) (value Value, isAddr bool) {
        if f.debugInfo() { // (opt)
                e = unparen(e)
                for _, b := range f.Blocks {
                        for _, instr := range b.Instrs {
                                if ref, ok := instr.(*DebugRef); ok {
                                        if ref.Expr == e {
                                                return ref.X, ref.IsAddr
                                        }
                                }
                        }
                }
        }
        return
}

// --- Lookup functions for source-level named entities (types.Objects) ---

// Package returns the SSA Package corresponding to the specified
// type-checker package object.
// It returns nil if no such SSA package has been created.
//
func (prog *Program) Package(obj *types.Package) *Package {
        return prog.packages[obj]
}

// packageLevelValue returns the package-level value corresponding to
// the specified named object, which may be a package-level const
// (*Const), var (*Global) or func (*Function) of some package in
// prog.  It returns nil if the object is not found.
//
func (prog *Program) packageLevelValue(obj types.Object) Value {
        if pkg, ok := prog.packages[obj.Pkg()]; ok {
                return pkg.values[obj]
        }
        return nil
}

// FuncValue returns the concrete Function denoted by the source-level
// named function obj, or nil if obj denotes an interface method.
//
// TODO(adonovan): check the invariant that obj.Type() matches the
// result's Signature, both in the params/results and in the receiver.
//
func (prog *Program) FuncValue(obj *types.Func) *Function {
        fn, _ := prog.packageLevelValue(obj).(*Function)
        return fn
}

// ConstValue returns the SSA Value denoted by the source-level named
// constant obj.
//
func (prog *Program) ConstValue(obj *types.Const) *Const {
        // TODO(adonovan): opt: share (don't reallocate)
        // Consts for const objects and constant ast.Exprs.

        // Universal constant? {true,false,nil}
        if obj.Parent() == types.Universe {
                return NewConst(obj.Val(), obj.Type())
        }
        // Package-level named constant?
        if v := prog.packageLevelValue(obj); v != nil {
                return v.(*Const)
        }
        return NewConst(obj.Val(), obj.Type())
}

// VarValue returns the SSA Value that corresponds to a specific
// identifier denoting the source-level named variable obj.
//
// VarValue returns nil if a local variable was not found, perhaps
// because its package was not built, the debug information was not
// requested during SSA construction, or the value was optimized away.
//
// ref is the path to an ast.Ident (e.g. from PathEnclosingInterval),
// and that ident must resolve to obj.
//
// pkg is the package enclosing the reference.  (A reference to a var
// always occurs within a function, so we need to know where to find it.)
//
// If the identifier is a field selector and its base expression is
// non-addressable, then VarValue returns the value of that field.
// For example:
//    func f() struct {x int}
//    f().x  // VarValue(x) returns a *Field instruction of type int
//
// All other identifiers denote addressable locations (variables).
// For them, VarValue may return either the variable's address or its
// value, even when the expression is evaluated only for its value; the
// situation is reported by isAddr, the second component of the result.
//
// If !isAddr, the returned value is the one associated with the
// specific identifier.  For example,
//       var x int    // VarValue(x) returns Const 0 here
//       x = 1        // VarValue(x) returns Const 1 here
//
// It is not specified whether the value or the address is returned in
// any particular case, as it may depend upon optimizations performed
// during SSA code generation, such as registerization, constant
// folding, avoidance of materialization of subexpressions, etc.
//
func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) (value Value, isAddr bool) {
        // All references to a var are local to some function, possibly init.
        fn := EnclosingFunction(pkg, ref)
        if fn == nil {
                return // e.g. def of struct field; SSA not built?
        }

        id := ref[0].(*ast.Ident)

        // Defining ident of a parameter?
        if id.Pos() == obj.Pos() {
                for _, param := range fn.Params {
                        if param.Object() == obj {
                                return param, false
                        }
                }
        }

        // Other ident?
        for _, b := range fn.Blocks {
                for _, instr := range b.Instrs {
                        if dr, ok := instr.(*DebugRef); ok {
                                if dr.Pos() == id.Pos() {
                                        return dr.X, dr.IsAddr
                                }
                        }
                }
        }

        // Defining ident of package-level var?
        if v := prog.packageLevelValue(obj); v != nil {
                return v.(*Global), true
        }

        return // e.g. debug info not requested, or var optimized away
}