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Add more expository comments to eval, and remove a useless parameter

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ridiculousfish 2015-01-07 14:56:41 -08:00
parent e045eabad6
commit 906d235601
2 changed files with 12 additions and 4 deletions
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2
exec.cpp
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@ -767,7 +767,7 @@ void exec_job(parser_t &parser, job_t *j)
However, eval does this: However, eval does this:
echo "begin; $argv "\n" ;end eval2_inner <&3 3<&-" | source 3<&0 echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0
which depends on the redirection being evaluated before the pipe. So the write end of the pipe comes first, the read pipe of the pipe comes last. See issue #966. which depends on the redirection being evaluated before the pipe. So the write end of the pipe comes first, the read pipe of the pipe comes last. See issue #966.
*/ */

14
share/functions/eval.fish
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@ -29,10 +29,9 @@ function eval -S -d "Evaluate parameters as a command"
end end
# rfish: To eval 'foo', we construct a block "begin ; foo; end <&3 3<&-" # rfish: To eval 'foo', we construct a block "begin ; foo; end <&3 3<&-"
# The 'eval2_inner' is a param to 'begin' itself; I believe it does nothing.
# Note the redirections are also within the quotes. # Note the redirections are also within the quotes.
# #
# We then pipe this to 'source 3<&0' which dup2's 3 to stdin. # We then pipe this to 'source 3<&0’.
# #
# You might expect that the dup2(3, stdin) should overwrite stdin, # You might expect that the dup2(3, stdin) should overwrite stdin,
# and therefore prevent 'source' from reading the piped-in block. This doesn't happen # and therefore prevent 'source' from reading the piped-in block. This doesn't happen
@ -40,8 +39,17 @@ function eval -S -d "Evaluate parameters as a command"
# of the block; instead we set a separate fd in a variable 'builtin_stdin', which is # of the block; instead we set a separate fd in a variable 'builtin_stdin', which is
# what it reads from. So builtins are magic in that, in pipes, their stdin # what it reads from. So builtins are magic in that, in pipes, their stdin
# is not fd 0. # is not fd 0.
#
# ‘source’ does not apply the redirections to itself. Instead it saves them and passes
# them as block-level redirections to parser.eval(). Ultimately the eval’d code sees
# the following redirections (in the following order):
# dup2 0 -> 3
# dup2 pipe -> 0
# dup2 3 -> 0
# where the pipe is the pipe we get from piping ‘echo’ to ‘source’. Thus the redirection
# effectively makes stdin fd0, instead of the thing that was piped to ‘source’
echo "begin; $argv "\n" ;end eval2_inner <&3 3<&-" | source 3<&0 echo "begin; $argv "\n" ;end <&3 3<&-" | source 3<&0
set -l res $status set -l res $status
status --job-control $mode status --job-control $mode