github.com/golangci/go-tools@v0.0.0-20190318060251-af6baa5dc196/functions/pure.go (about)

     1  package functions
     2  
     3  import (
     4  	"go/token"
     5  	"go/types"
     6  
     7  	"github.com/golangci/go-tools/callgraph"
     8  	"github.com/golangci/go-tools/lint/lintdsl"
     9  	"github.com/golangci/go-tools/ssa"
    10  )
    11  
    12  // IsStub reports whether a function is a stub. A function is
    13  // considered a stub if it has no instructions or exactly one
    14  // instruction, which must be either returning only constant values or
    15  // a panic.
    16  func (d *Descriptions) IsStub(fn *ssa.Function) bool {
    17  	if len(fn.Blocks) == 0 {
    18  		return true
    19  	}
    20  	if len(fn.Blocks) > 1 {
    21  		return false
    22  	}
    23  	instrs := lintdsl.FilterDebug(fn.Blocks[0].Instrs)
    24  	if len(instrs) != 1 {
    25  		return false
    26  	}
    27  
    28  	switch instrs[0].(type) {
    29  	case *ssa.Return:
    30  		// Since this is the only instruction, the return value must
    31  		// be a constant. We consider all constants as stubs, not just
    32  		// the zero value. This does not, unfortunately, cover zero
    33  		// initialised structs, as these cause additional
    34  		// instructions.
    35  		return true
    36  	case *ssa.Panic:
    37  		return true
    38  	default:
    39  		return false
    40  	}
    41  }
    42  
    43  func (d *Descriptions) IsPure(fn *ssa.Function) bool {
    44  	if fn.Signature.Results().Len() == 0 {
    45  		// A function with no return values is empty or is doing some
    46  		// work we cannot see (for example because of build tags);
    47  		// don't consider it pure.
    48  		return false
    49  	}
    50  
    51  	for _, param := range fn.Params {
    52  		if _, ok := param.Type().Underlying().(*types.Basic); !ok {
    53  			return false
    54  		}
    55  	}
    56  
    57  	if fn.Blocks == nil {
    58  		return false
    59  	}
    60  	checkCall := func(common *ssa.CallCommon) bool {
    61  		if common.IsInvoke() {
    62  			return false
    63  		}
    64  		builtin, ok := common.Value.(*ssa.Builtin)
    65  		if !ok {
    66  			if common.StaticCallee() != fn {
    67  				if common.StaticCallee() == nil {
    68  					return false
    69  				}
    70  				// TODO(dh): ideally, IsPure wouldn't be responsible
    71  				// for avoiding infinite recursion, but
    72  				// FunctionDescriptions would be.
    73  				node := d.CallGraph.CreateNode(common.StaticCallee())
    74  				if callgraph.PathSearch(node, func(other *callgraph.Node) bool {
    75  					return other.Func == fn
    76  				}) != nil {
    77  					return false
    78  				}
    79  				if !d.Get(common.StaticCallee()).Pure {
    80  					return false
    81  				}
    82  			}
    83  		} else {
    84  			switch builtin.Name() {
    85  			case "len", "cap", "make", "new":
    86  			default:
    87  				return false
    88  			}
    89  		}
    90  		return true
    91  	}
    92  	for _, b := range fn.Blocks {
    93  		for _, ins := range b.Instrs {
    94  			switch ins := ins.(type) {
    95  			case *ssa.Call:
    96  				if !checkCall(ins.Common()) {
    97  					return false
    98  				}
    99  			case *ssa.Defer:
   100  				if !checkCall(&ins.Call) {
   101  					return false
   102  				}
   103  			case *ssa.Select:
   104  				return false
   105  			case *ssa.Send:
   106  				return false
   107  			case *ssa.Go:
   108  				return false
   109  			case *ssa.Panic:
   110  				return false
   111  			case *ssa.Store:
   112  				return false
   113  			case *ssa.FieldAddr:
   114  				return false
   115  			case *ssa.UnOp:
   116  				if ins.Op == token.MUL || ins.Op == token.AND {
   117  					return false
   118  				}
   119  			}
   120  		}
   121  	}
   122  	return true
   123  }