Inherit context from source sites

[lionel-]

Progress towards posit-dev/positron#14790
Progress towards #1338

Previously, only the source() site would see sourced context (top-level bindings and transitive Source and Attach effects). With this PR, the sourced file now sees the context from the source site too.

In a way, this is a more principled mechanism for the R/ auto-collation mechanism of the previous PR. In another way, this is a bit unprincipled, as standalone files are much easier to analyse, both by static analysis tools and by humans (https://github.com/include-what-you-use/include-what-you-use/blob/master/docs/WhyIWYU.md).

When both the R/ auto-collation and the inherited source site apply, the latter wins: a resolved source() is a better signal than the directory-name convention. They should possibly union, since e.g. a Shiny-style autoload really does happen alongside. We can refine later.

# file1.R
x <- 1
source("foo.R")

# file2.R
x <- 1
y <- 2
source("foo.R")

# foo.R
list(x, y)

Now when you goto-def of x in foo.R, you'll see both file1.R and file2.R targets. Note how y is conditionally undefined: this will need to be linted once we implement Oak-based symbol diagnostics.

For now we have two new experimental diagnostics for effects ambiguity:

1. source-cycle, when files source each other:

# a.R
source("b.R")

# b.R
source("a.R")

warning[source-cycle]: This file takes part in a cycle of mutual source() calls. Language analysis will be incomplete until the cycle is resolved.

2. inherited-shadow, when an inherited binding changes what a callee resolves to:

# a.R
source <- identity
base::source("b.R")

# b.R
source("c.R")

info[inherited-shadow]: This source call has an ambiguous effect. It resolves through package base when the file is sourced on its own, and to a binding in a.R when sourced by a.R.

Positron Release Notes

New Features

• Sourced files now see the context inherited from the source() location, allowing you to navigate to the inherited symbols or rename them.

Bug Fixes

• N/A