Fix definition(String, m) for methods defined at the REPL

Fixes #28. Note this revealed a number of other concerns, most
notably that stripping the first and last character made strong
assumptions about what those characters were. This now just strips
leading and trailing '\n', which is technically a breaking change.

Author: timholy

src/CodeTracking.jl

@@ -115,7 +115,7 @@ Returns `nothing` if there are no methods at that location.
 """
 function signatures_at(filename::AbstractString, line::Integer)
     if !startswith(filename, "REPL[")
-        filename =  abspath(filename)
+        filename = abspath(filename)
     end
     if occursin(juliabase, filename)
         rpath = postpath(filename, juliabase)
@@ -188,17 +188,18 @@ see [`definition(Expr, method::Method)`](@ref) instead.
 """
 function definition(::Type{String}, method::Method)
     file, line = whereis(method)
-    src = read(file, String)
+    src = src_from_file_or_REPL(file)
     eol = isequal('\n')
     linestarts = Int[]
-    istart = 0
+    istart = 1
     for i = 1:line-1
-        push!(linestarts, istart+1)
-        istart = findnext(eol, src, istart+1)
+        push!(linestarts, istart)
+        istart = findnext(eol, src, istart) + 1
     end
     ex, iend = Meta.parse(src, istart)
     if isfuncexpr(ex)
-        return src[istart+1:iend-1], line
+        iend = min(iend, lastindex(src))
+        return strip(src[istart:iend], '\n'), line
     end
     # The function declaration was presumably on a previous line
     lineindex = lastindex(linestarts)

src/utils.jl

@@ -39,6 +39,35 @@ fileline(lnn::LineNumberNode) = String(lnn.file), lnn.line
 # This is piracy, but it's not ambiguous in terms of what it should do
 Base.convert(::Type{LineNumberNode}, lin::LineInfoNode) = LineNumberNode(lin.line, lin.file)
 
+# This regex matches the pseudo-file name of a REPL history entry.
+const rREPL = r"^REPL\[(\d+)\]$"
+
+"""
+    src = src_from_file_or_REPL(origin::AbstractString, repl = Base.active_repl)
+
+Read the source for a function from `origin`, which is either the name of a file
+or "REPL[\$i]", where `i` is an integer specifying the particular history entry.
+Methods defined at the REPL use strings of this form in their `file` field.
+
+If you happen to have a file where the name matches `REPL[\$i]`, first pass it through
+`abspath`.
+"""
+function src_from_file_or_REPL(origin::AbstractString, args...)
+    # This Varargs design prevents an unnecessary error when Base.active_repl is undefined
+    # and `origin` does not match "REPL[$i]"
+    m = match(rREPL, origin)
+    if m !== nothing
+        return _src_from_file_or_REPL(origin, args...)
+    end
+    return read(origin, String)
+end
+
+function _src_from_file_or_REPL(origin::AbstractString, repl = Base.active_repl)
+    hist_idx = parse(Int, m.captures[1])
+    hp = repl.interface.modes[1].hist
+    return hp.history[hp.start_idx+hist_idx]
+end
+
 function basepath(id::PkgId)
     id.name ∈ ("Main", "Base", "Core") && return ""
     loc = Base.locate_package(id)

test/runtests.jl

@@ -31,9 +31,7 @@ isdefined(Main, :Revise) ? includet("script.jl") : include("script.jl")
 
     m = first(methods(f2))
     src, line = definition(String, m)
-    @test src == """
-    f2(x, y) = x + y
-    """
+    @test src == "f2(x, y) = x + y"
     @test line == 7
 
     info = CodeTracking.PkgFiles(Base.PkgId(CodeTracking))
@@ -62,6 +60,17 @@ isdefined(Main, :Revise) ? includet("script.jl") : include("script.jl")
     # Test with broken lookup
     CodeTracking.method_lookup_callback[] = m -> error("oops")
     @test whereis(m) == ("REPL[1]", 1)
+    # Test with definition(String, m)
+    if isdefined(Base, :active_repl)
+        hp = Base.active_repl.interface.modes[1].hist
+        fstr = "__fREPL__(x::Int16) = 0"
+        histidx = length(hp.history) + 1 - hp.start_idx
+        ex = Base.parse_input_line(fstr; filename="REPL[$histidx]")
+        f = Core.eval(Main, ex)
+        push!(hp.history, fstr)
+        @test definition(String, first(methods(f))) == (fstr, 1)
+        pop!(hp.history)
+    end
 
     m = first(methods(Test.eval))
     @test occursin(Sys.STDLIB, whereis(m)[1])