[workspace] Update ALIAS_REPOSITORIES to read dicts of aliases

[bobpaw]

The list of bazel repository aliases used to always be {name: actual}. Now that more will be maps, adjust the logic to support them naturally instead of as edge cases.

re: #24913 (review)

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This change is 

[bobpaw]

+a:@tyler-yankee

[tyler-yankee]

holding off on review until the implementation is working...

@tyler-yankee reviewed 1 file and all commit messages, and made 2 comments.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee tyler-yankee, needs platform reviewer assigned, needs at least two assigned reviewers (waiting on bobpaw).

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-- commits line 5 at r1:
nit the phrasing "Now that more" is slightly awkward to me. Consider e.g.:

The assumed `{name: actual}` mapping is inflexible as the number of packages
using this helper grows in the future.

[tyler-yankee]

@tyler-yankee reviewed 1 file and all commit messages, made 3 comments, and resolved 1 discussion.
Reviewable status: 3 unresolved discussions, LGTM missing from assignee tyler-yankee, needs platform reviewer assigned, needs at least two assigned reviewers (waiting on bobpaw).

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tools/workspace/default.bzl line 184 at r2 (raw file):

    }

    for name in ALIAS_REPOSITORIES:

nit can we get away with for name, alias in ALIAS_REPOSITORIES.items() in Starlark?

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tools/workspace/default.bzl line 185 at r2 (raw file):

    for name in ALIAS_REPOSITORIES:
        alias_root = "@drake//tools/workspace/"

nit I suppose we can define this outside the loop.

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tools/workspace/default.bzl line 192 at r2 (raw file):

            aliases = {n: alias_root + a for n, a in alias.items()}
        else:
            aliases = {name: alias_root + name}

This is never taken, right? Can't weif str ... else assert dict ...?

Code quote:

        else:
            aliases = {name: alias_root + name}

[bobpaw]

tools/workspace/default.bzl line 192 at r2 (raw file):

Previously, tyler-yankee (Tyler Yankee) wrote…

This is never taken, right? Can't weif str ... else assert dict ...?

Will do and I think starlark needs fail not assert

[bobpaw]

@bobpaw made 1 comment and resolved 2 discussions.
Reviewable status: 1 unresolved discussion, LGTM missing from assignee tyler-yankee, needs platform reviewer assigned, needs at least two assigned reviewers (waiting on tyler-yankee).

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tools/workspace/default.bzl line 192 at r2 (raw file):

Previously, bobpaw (Aiden Woodruff) wrote…

Will do and I think starlark needs fail not assert

Done.

[tyler-yankee]

feature

@tyler-yankee reviewed 1 file and all commit messages, made 1 comment, and resolved 1 discussion.
Reviewable status: needs platform reviewer assigned, needs at least two assigned reviewers (waiting on bobpaw).

[tyler-yankee]

+a:@SeanCurtis-TRI for platform review per schedule, please.

@tyler-yankee made 1 comment.
Reviewable status: LGTM missing from assignee SeanCurtis-TRI(platform) (waiting on SeanCurtis-TRI).

[SeanCurtis-TRI]

@SeanCurtis-TRI reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: complete! all discussions resolved, LGTM from assignees tyler-yankee,SeanCurtis-TRI(platform) (waiting on bobpaw).