From 959eb4cb8ed2a9bfc0fba1e3ea65e8873efa7bb0 Mon Sep 17 00:00:00 2001
From: Felipe Noronha <felipenoris@gmail.com>
Date: Thu, 27 Aug 2015 00:25:44 -0300
Subject: [PATCH] Raise informative error for float/integer exponentiation that
 yields Complex

Same as #3024
---
 base/replutil.jl | 23 +++++++++++++----------
 test/math.jl     |  5 +++++
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/base/replutil.jl b/base/replutil.jl
index 4b0ca4437cc01..e5c8f4e3f4a73 100644
--- a/base/replutil.jl
+++ b/base/replutil.jl
@@ -106,11 +106,14 @@ function showerror(io::IO, ex::DomainError, bt; backtrace=true)
         code = ccall(:jl_lookup_code_address, Any, (Ptr{Void}, Cint), b-1, true)
         if length(code) == 5 && !code[4]  # code[4] == fromC
             if code[1] in (:log, :log2, :log10, :sqrt) # TODO add :besselj, :besseli, :bessely, :besselk
-                println(io,"\n$(code[1]) will only return a complex result if called with a complex argument.")
-                print(io, "try $(code[1]) (complex(x))")
-            elseif (code[1] == :^ && code[2] == symbol("intfuncs.jl")) || code[1] == :power_by_squaring
-                println(io, "\nCannot raise an integer x to a negative power -n. Make x a float by adding")
-                print(io, "a zero decimal (e.g. 2.0^-n instead of 2^-n), or write 1/x^n, float(x)^-n, or (x//1)^-n")
+                println(io,"\n$(code[1]) will only return a complex result if called with a complex argument. ",
+                        "Try $(code[1]) (complex(x)).")
+            elseif (code[1] == :^ && code[2] == symbol("intfuncs.jl")) || code[1] == :power_by_squaring #3024
+                println(io, "\nCannot raise an integer x to a negative power -n. \nMake x a float by adding ",
+                        "a zero decimal (e.g. 2.0^-n instead of 2^-n), or write 1/x^n, float(x)^-n, or (x//1)^-n.")
+            elseif code[1] == :^ && (code[2] == symbol("promotion.jl") || code[2] == symbol("math.jl"))
+                println(io, "\nExponentiation yielding a complex result requires a complex argument. ",
+                        "\nReplace x^y with (x+0im)^y, Complex(x)^y, or similar.")
             end
             break
         end
@@ -173,9 +176,9 @@ function showerror(io::IO, ex::MethodError)
             push!(vec_args, isrow ? vec(arg) : arg)
         end
         if hasrows && applicable(f, vec_args...)
-            print(io, "\n\nYou might have used a 2d row vector where a 1d column vector was required.")
-            print(io, "\nNote the difference between 1d column vector [1,2,3] and 2d row vector [1 2 3].")
-            print(io, "\nYou can convert to a column vector with the vec() function.")
+            print(io, "\n\nYou might have used a 2d row vector where a 1d column vector was required.",
+                      "\nNote the difference between 1d column vector [1,2,3] and 2d row vector [1 2 3].",
+                      "\nYou can convert to a column vector with the vec() function.")
         end
     end
     # Give a helpful error message if the user likely called a type constructor
@@ -185,8 +188,8 @@ function showerror(io::IO, ex::MethodError)
         arg_types_param[1].name === Type.name)
         construct_type = arg_types_param[1].parameters[1]
         println(io)
-        print(io, "This may have arisen from a call to the constructor $construct_type(...),")
-        print(io, "\nsince type constructors fall back to convert methods.")
+        print(io, "This may have arisen from a call to the constructor $construct_type(...),",
+                  "\nsince type constructors fall back to convert methods.")
     end
     show_method_candidates(io, ex)
 end
diff --git a/test/math.jl b/test/math.jl
index 9413df6ea4b1d..f8d3f7f1a8095 100644
--- a/test/math.jl
+++ b/test/math.jl
@@ -542,3 +542,8 @@ for f in binary_math_functions
     @test f(x,[y]) == v
     @test f([x],[y]) == v
 end
+
+# #3024, #12822
+@test_throws DomainError 2 ^ -2
+@test_throws DomainError (-2)^(2.2)
+@test_throws DomainError (-2.0)^(2.2)