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| -rw-r--r-- | doc/future-designs/multiple-mrrc.md | 60 |
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diff --git a/doc/future-designs/multiple-mrrc.md b/doc/future-designs/multiple-mrrc.md new file mode 100644 index 00000000..a228a5b9 --- /dev/null +++ b/doc/future-designs/multiple-mrrc.md @@ -0,0 +1,60 @@ +# Multiple rc files for `just-mr` + +## Current situation and shortcomings + +Upon startup, `just-mr` reads a single rc file to set various defaults, +including remote-execution endpoint and early arguments for the +various `just` subcommands, if used as a launcher. By default, the +rc file read is the file `~/.just-mrrc`, if it exists. A different +rc file can be specified via the `--rc` option. Moreover, by givining +`--norc` the reading of an rc file can be disabled entirely. + +Using a global rc file works fine when working on a single project +or when only building locally. However, when working on several +projects, it quickly becomes necessary to switch between various +configurations of the build set up. + +Different projects might have different default build configurations, +dispatch to different execution-property-specific endpoints, or +consider different repositories absent. Due to the ability to +specify a workspace-relative file name in the just-mr rc file these +different set ups can be managed by committing the respective files +in to the repository. + +However, different projects, also use different build images, +reflected by different remote-execution properties; some might even +use different remote-execution end points or differ in the serve +end point they use (or whether a serve end point is used at all). +Especially for the remote-execution properties used, it is desirable +to version those in the repository. A change of the remote-execution +property usually reflects the use of a different build environment +and properly versioning such change is important when reconstructing +old binaries or when bisecting to find a breakage. + +The current solution is to commit the respective rc file for `just-mr` +and expect the user to provide the respective `--rc` option. While +this works in principle, it causes additional inconvenience when +working deep inside a subdirectory of the project, and often causes +build attempts in unintended `just-mr` configurations due to a +forgotten or wrong `--rc` argument. + +## Proposed changes + +We propose to add a new field `"rc files"` that, if given, contains +a list of location objects. After reading the main rc file, those +location objects will be processed in the given order; if a file +exists at the specified location, it will be read as an additional +rc file, however ignoring a possibly given `"rc files"` field. If +values are specified in several rc files, the latest value wins. + +Only after all the rc files are read, the resulting rc configuration +is evaluated. In particular, a later rc file can override an earlier +specification of the search order for the repository config, or +for individual `"just files"`. + +In this way it is possible, by simply specifying the naming +conventions used, to automatically use the committed rc-files for +the project of the current working directory. The global rc file +can also specify useful defaults; if necessary, it is also possible +to specify hard overrides, by specifying a corresponding file in +the user's home directory at the very and of the list. |