Source file src/cmd/vendor/golang.org/x/tools/go/analysis/passes/internal/analysisutil/util.go

     1	// Package analysisutil defines various helper functions
     2	// used by two or more packages beneath go/analysis.
     3	package analysisutil
     4	
     5	import (
     6		"bytes"
     7		"go/ast"
     8		"go/printer"
     9		"go/token"
    10		"go/types"
    11		"io/ioutil"
    12	)
    13	
    14	// Format returns a string representation of the expression.
    15	func Format(fset *token.FileSet, x ast.Expr) string {
    16		var b bytes.Buffer
    17		printer.Fprint(&b, fset, x)
    18		return b.String()
    19	}
    20	
    21	// HasSideEffects reports whether evaluation of e has side effects.
    22	func HasSideEffects(info *types.Info, e ast.Expr) bool {
    23		safe := true
    24		ast.Inspect(e, func(node ast.Node) bool {
    25			switch n := node.(type) {
    26			case *ast.CallExpr:
    27				typVal := info.Types[n.Fun]
    28				switch {
    29				case typVal.IsType():
    30					// Type conversion, which is safe.
    31				case typVal.IsBuiltin():
    32					// Builtin func, conservatively assumed to not
    33					// be safe for now.
    34					safe = false
    35					return false
    36				default:
    37					// A non-builtin func or method call.
    38					// Conservatively assume that all of them have
    39					// side effects for now.
    40					safe = false
    41					return false
    42				}
    43			case *ast.UnaryExpr:
    44				if n.Op == token.ARROW {
    45					safe = false
    46					return false
    47				}
    48			}
    49			return true
    50		})
    51		return !safe
    52	}
    53	
    54	// Unparen returns e with any enclosing parentheses stripped.
    55	func Unparen(e ast.Expr) ast.Expr {
    56		for {
    57			p, ok := e.(*ast.ParenExpr)
    58			if !ok {
    59				return e
    60			}
    61			e = p.X
    62		}
    63	}
    64	
    65	// ReadFile reads a file and adds it to the FileSet
    66	// so that we can report errors against it using lineStart.
    67	func ReadFile(fset *token.FileSet, filename string) ([]byte, *token.File, error) {
    68		content, err := ioutil.ReadFile(filename)
    69		if err != nil {
    70			return nil, nil, err
    71		}
    72		tf := fset.AddFile(filename, -1, len(content))
    73		tf.SetLinesForContent(content)
    74		return content, tf, nil
    75	}
    76	
    77	// LineStart returns the position of the start of the specified line
    78	// within file f, or NoPos if there is no line of that number.
    79	func LineStart(f *token.File, line int) token.Pos {
    80		// Use binary search to find the start offset of this line.
    81		//
    82		// TODO(adonovan): eventually replace this function with the
    83		// simpler and more efficient (*go/token.File).LineStart, added
    84		// in go1.12.
    85	
    86		min := 0        // inclusive
    87		max := f.Size() // exclusive
    88		for {
    89			offset := (min + max) / 2
    90			pos := f.Pos(offset)
    91			posn := f.Position(pos)
    92			if posn.Line == line {
    93				return pos - (token.Pos(posn.Column) - 1)
    94			}
    95	
    96			if min+1 >= max {
    97				return token.NoPos
    98			}
    99	
   100			if posn.Line < line {
   101				min = offset
   102			} else {
   103				max = offset
   104			}
   105		}
   106	}
   107	

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