Fix incorrect source info in docstrings

Fixes JuliaLang#36906, where source info wasn't being passed through
at-doc when it was applied to definitions defined within macros.

base/docs/Docs.jl

@@ -443,22 +443,22 @@ more than one expression is marked then the same docstring is applied to each ex
 """
 :(Core.@__doc__)
 
-function __doc__!(meta, def, define::Bool)
-    @nospecialize meta def
+function __doc__!(source, mod, meta, def, define::Bool)
+    @nospecialize source mod meta def
     # Two cases must be handled here to avoid redefining all definitions contained in `def`:
     if define
         # `def` has not been defined yet (this is the common case, i.e. when not generating
         # the Base image). We just need to convert each `@__doc__` marker to an `@doc`.
         finddoc(def) do each
             each.head = :macrocall
-            each.args = [Symbol("@doc"), nothing, meta, each.args[end], define] # TODO: forward line number info
+            each.args = [Symbol("@doc"), source, mod, nothing, meta, each.args[end], define]
         end
     else
         # `def` has already been defined during Base image gen so we just need to find and
         # document any subexpressions marked with `@__doc__`.
         docs  = []
         found = finddoc(def) do each
-            push!(docs, :(@doc($meta, $(each.args[end]), $define)))
+            push!(docs, :(@doc($source, $mod, $meta, $(each.args[end]), $define)))
         end
         # If any subexpressions have been documented then replace the entire expression with
         # just those documented subexpressions to avoid redefining any definitions.
@@ -509,6 +509,8 @@ function docm(source::LineNumberNode, mod::Module, ex)
         return REPL.lookup_doc(ex)
     end
 end
+# Drop incorrect line numbers produced by nested macro calls.
+docm(source::LineNumberNode, mod::Module, _, _, x...) = docm(source, mod, x...)
 
 # iscallexpr checks if an expression is a :call expression. The call expression may be
 # also part of a :where expression, so it unwraps the :where layers until it reaches the
@@ -578,7 +580,7 @@ function docm(source::LineNumberNode, mod::Module, meta, ex, define::Bool = true
     # Errors generated by calling `macroexpand` are passed back to the call site.
     isexpr(x, :error) ? esc(x) :
     # When documenting macro-generated code we look for embedded `@__doc__` calls.
-    __doc__!(meta, x, define) ? esc(x) :
+    __doc__!(source, mod, meta, x, define) ? esc(x) :
     # Any "basic" expression such as a bare function or module name or numeric literal.
     isbasicdoc(x) ? objectdoc(source, mod, meta, nothing, x) :
 

test/docs.jl

@@ -433,6 +433,7 @@ macro example_1(f)
     end |> esc
 end
 
+const LINE_NUMBER_F = @__LINE__() + 1
 "f"
 @example_1 f
 
@@ -446,16 +447,23 @@ macro example_2(f)
     end |> esc
 end
 
+const LINE_NUMBER_G = @__LINE__() + 1
 "g"
 @example_2 g
 
 @example_2 _g
 
+const LINE_NUMBER_T = @__LINE__() + 1
+"T"
+Base.@kwdef struct T end
+
 end
 
 let md = meta(MacroGenerated)[@var(MacroGenerated.f)]
     @test md.order == [Tuple{Any}]
     @test docstrings_equal(md.docs[Tuple{Any}], doc"f")
+    @test md.docs[Tuple{Any}].data[:linenumber] == MacroGenerated.LINE_NUMBER_F
+    @test md.docs[Tuple{Any}].data[:path] == @__FILE__()
 end
 
 @test isdefined(MacroGenerated, :_f)
@@ -464,10 +472,19 @@ let md = meta(MacroGenerated)[@var(MacroGenerated.g)]
     @test md.order == [Tuple{Any}, Tuple{Any, Any}]
     @test docstrings_equal(md.docs[Tuple{Any}], doc"g")
     @test docstrings_equal(md.docs[Tuple{Any, Any}], doc"g")
+    @test md.docs[Tuple{Any}].data[:linenumber] == MacroGenerated.LINE_NUMBER_G
+    @test md.docs[Tuple{Any}].data[:path] == @__FILE__()
 end
 
 @test isdefined(MacroGenerated, :_g)
 
+let md = meta(MacroGenerated)[@var(MacroGenerated.T)]
+    @test md.order == Type[Union{}]
+    @test docstrings_equal(md.docs[Union{}], doc"T")
+    @test md.docs[Union{}].data[:linenumber] == MacroGenerated.LINE_NUMBER_T
+    @test md.docs[Union{}].data[:path] == @__FILE__()
+end
+
 module DocVars
 
 struct __FIELDS__ end