Hi all,
Mathias LANG and me have been working on fixing a regression in
Dub's variable expansion implementation [1]. Background:
In order to support use cases where a variable is used as a
prefix or suffix in an identifier-like strings (e.g.
build/${DUB_PACKAGE}_${DUB_PLATFORM}_${DUB_ARCH}), pull request
[2] added support for syntax ${var}, in addition to the existing
$var syntax.
Unfortunately that PR broke dollar sign escaping ($$) which was
not caught by neither Dub's own unit tests, integration tests,
nor any of the 46 Dub packages tested on Buildkite [4] (our CI
for testing each pull request to dmd/druntime/phobos/tools/dub).
However, while testing the fix that Mathias originally wrote I
bumped into a couple of edge cases and I realized the expected
behavior is not thoroughly documented. As per the docs [4]:
Inside of build setting values, it is possible to use variables
using dollar notation. Any variable not matching a predefined
name will be taken from the program environment. To denote a
literal dollar sign, use $$.
Should dollar signs not followed by a variable identifier be left
as they are? What about escaped dollar signs ($$), or even $$$,
$$$$, etc.? And what about $$$var?
For the purposes of this discussion, if we assume that each
variable $var1 or ${var2} will be replaced by <VAR1> and <VAR2>
respectively, which of the following outputs is the correct for
the given input?
Source code:
https://run.dlang.io/gist/ZombineDev/eaf7076a7b83a556fac0c058b0525270?compiler=dmd
Input:
$ $$ $$$ $$$$ $$$$$ $$$$$$
asd$$var1$var2$var3${var4}${var5}$${var6}$$var7$${var8} a$var9
b$$var10 c$$$var11 d$$$$var12 e$$$$$var13 f$$$$$$var14
g$$$$$$$var15 h$$$$$$$$var16 $$&$!$$?$$$$var18
Petar#1:
$ $$ $$$ $$$$ $$$$$ $$$$$$
asd$var1<VAR2><VAR3><VAR4><VAR5>${var6}$var7${var8} a<VAR9>
b$var10 c$$var11 d$$$var12 e$$$$var13 f$$$$$var14 g$$$$$$var15
h$$$$$$$var16 $$&$!$$?$$$var18
Petar#2:
$ $ $$ $$ $$$ $$$
asd$var1<VAR2><VAR3><VAR4><VAR5>${var6}$var7${var8} a<VAR9>
b$var10 c$<VAR11> d$$var12 e$$<VAR13> f$$$var14 g$$$<VAR15>
h$$$$var16 $&$!$?$$var18
Mathias#1:
$ $ $$ $$ $$$ $$$
asd$var1<VAR2>$var3<VAR4>${var5}${var6}$var7${var8} a<VAR9>
b$var10 c$$var11 d$$var12 e$$$var13 f$$$var14 g$$$$var15
h$$$$var16 $&$!$?$$var18
Martin:
$ $$ $$$ $$$$ $$$$$ $$$$$$
asd$<VAR1><VAR2><VAR3><VAR4><VAR5>$<VAR6>$<VAR7>$<VAR8> a<VAR9>
b$<VAR10> c$$<VAR11> d$$$<VAR12> e$$$$<VAR13> f$$$$$<VAR14>
g$$$$$$<VAR15> h$$$$$$$<VAR16> $$&$!$$?$$$<VAR18>
Original:
<> $ $<> $$ $$<> $$$
asd$var1<VAR2><VAR3><>{var4}<>{var5}${var6}$var7${var8} a<VAR9>
b$var10 c$<VAR11> d$$var12 e$$<VAR13> f$$$var14 g$$$<VAR15>
h$$$$var16 $&<>!$?$$var18
Other: ???
Cheers,
Petar
[1]: https://github.com/dlang/dub/pull/1552
[2]: https://github.com/dlang/dub/pull/1392
[3]:
https://gist.github.com/ZombineDev/fd79c4ffd58dbe9792d799f66b7f9434
[4]:
https://code.dlang.org/package-format?lang=json#environment-variables
