Return nothing for methods with line == 0

src/CodeTracking.jl

@@ -183,13 +183,15 @@ end
 
 Return a string with the code that defines `method`. Also return the first line of the
 definition, including the signature (which may not be the same line number returned
-by `whereis`).
+by `whereis`). If the method can't be located (line number 0), then `definition`
+instead returns `nothing.`
 
 Note this may not be terribly useful for methods that are defined inside `@eval` statements;
 see [`definition(Expr, method::Method)`](@ref) instead.
 """
 function definition(::Type{String}, method::Method)
     file, line = whereis(method)
+    line == 0 && return nothing
     src = src_from_file_or_REPL(file)
     eol = isequal('\n')
     linestarts = Int[]
@@ -222,7 +224,8 @@ end
     ex = definition(Expr, method::Method)
     ex = definition(method::Method)
 
-Return an expression that defines `method`.
+Return an expression that defines `method`. If the definition can't be found,
+returns `nothing`.
 """
 function definition(::Type{Expr}, method::Method)
     file = String(method.file)

test/runtests.jl

@@ -68,6 +68,7 @@ isdefined(Main, :Revise) ? includet("script.jl") : include("script.jl")
     m = first(methods(replfunc))
     @test whereis(m) == ("REPL[1]", 1)
     # Test with broken lookup
+    oldlookup = CodeTracking.method_lookup_callback[]
     CodeTracking.method_lookup_callback[] = m -> error("oops")
     @test whereis(m) == ("REPL[1]", 1)
     # Test with definition(String, m)
@@ -81,6 +82,7 @@ isdefined(Main, :Revise) ? includet("script.jl") : include("script.jl")
         @test definition(String, first(methods(f))) == (fstr, 1)
         pop!(hp.history)
     end
+    CodeTracking.method_lookup_callback[] = oldlookup
 
     m = first(methods(Test.eval))
     @test occursin(Sys.STDLIB, whereis(m)[1])
@@ -96,6 +98,20 @@ isdefined(Main, :Revise) ? includet("script.jl") : include("script.jl")
     lin = src.linetable[idx]
     file, line = whereis(lin, m)
     @test endswith(file, String(lin.file))
+
+    # Issues raised in #48
+    m = @which(sum([1]; dims=1))
+    if !isdefined(Main, :Revise)
+        def = definition(String, m)
+        @test def === nothing || isa(def[1], AbstractString)
+        def = definition(Expr, m)
+        @test def === nothing || isa(def, Expr)
+    else
+        def = definition(String, m)
+        @test isa(def[1], AbstractString)
+        def = definition(Expr, m)
+        @test isa(def, Expr)
+    end
 end
 
 @testset "With Revise" begin