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The following commit message is a squash of several commit messages.
- This is the 1st commit message:
Add position to stub error messages
Stub errors happen when we've started the initialization of a symbol but
key information of this symbol is missing (the information cannot be
found in any entry of the classpath not sources).
When this error happens, we better have a good error message with a
position to the place where the stub error came from. This commit goes
into this direction by adding a `pos` value to `StubSymbol` and filling
it in in all the use sites (especifically `UnPickler`).
This commit also changes some tests that test stub errors-related
issues. Concretely, `t6440` is using special Partest infrastructure and
doens't pretty print the position, while `t5148` which uses the
conventional infrastructure does. Hence the difference in the changes
for both tests.
- This is the commit message #2:
Add partest infrastructure to test stub errors
`StubErrorMessageTest` is the friend I introduce in this commit to help
state stub errors. The strategy to test them is easy and builds upon
previous concepts: we reuse `StoreReporterDirectTest` and add some
methods that will compile the code and simulate a missing classpath
entry by removing the class files from the class directory (the folder
where Scalac compiles to).
This first iteration allow us to programmatically check that stub errors
are emitted under certain conditions.
- This is the commit message #3:
Improve contents of stub error message
This commit does three things:
* Keep track of completing symbol while unpickling
First, it removes the previous `symbolOnCompletion` definition to be
more restrictive/clear and use only positions, since only positions are
used to report the error (the rest of the information comes from the
context of the `UnPickler`).
Second, it adds a new variable called `lazyCompletingSymbol` that is
responsible for keeping a reference to the symbol that produces the stub
error. This symbol will usually (always?) come from the classpath
entries and therefore we don't have its position (that's why we keep
track of `symbolOnCompletion` as well). This is the one that we have to
explicitly use in the stub error message, the culprit so to speak.
Aside from these two changes, this commit modifies the existing tests
that are affected by the change in the error message, which is more
precise now, and adds new tests for stub errors that happen in complex
inner cases and in return type of `MethodType`.
* Check that order of initialization is correct
With the changes introduced previously to keep track of position of
symbols coming from source files, we may ask ourselves: is this going to
work always? What happens if two symbols the initialization of two
symbols is intermingled and the stub error message gets the wrong
position?
This commit adds a test case and modifications to the test
infrastructure to double check empirically that this does not happen.
Usually, this interaction in symbol initialization won't happen because
the `UnPickler` will lazily load all the buckets necessary for a symbol
to be truly initialized, with the pertinent addresses from which this
information has to be deserialized. This ensures that this operation is
atomic and no other symbol initialization can happen in the meantime.
Even though the previous paragraph is the feeling I got from reading the
sources, this commit creates a test to double-check it. My attempt to be
better safe than sorry.
* Improve contents of the stub error message
This commit modifies the format of the previous stub error message by
being more precise in its formulation. It follows the structured format:
```
s"""|Symbol '${name.nameKind} ${owner.fullName}.$name' is missing from the classpath.
|This symbol is required by '${lazyCompletingSymbol.kindString} ${lazyCompletingSymbol.fullName}'.
```
This format has the advantage that is more readable and explicit on
what's happening. First, we report what is missing. Then, why it was
required. Hopefully, people working on direct dependencies will find the
new message friendlier.
Having a good test suite to check the previously added code is
important. This commit checks that stub errors happen in presence of
well-known and widely used Scala features. These include:
* Higher kinded types.
* Type definitions.
* Inheritance and subclasses.
* Typeclasses and implicits.
- This is the commit message #4:
Use `lastTreeToTyper` to get better positions
The previous strategy to get the last user-defined position for knowing
what was the root cause (the trigger) of stub errors relied on
instrumenting `def info`.
This instrumentation, while easy to implement, is inefficient since we
register the positions for symbols that are already completed.
However, we cannot do it only for uncompleted symbols (!hasCompleteInfo)
because the positions won't be correct anymore -- definitions using stub
symbols (val b = new B) are for the compiler completed, but their use
throws stub errors. This means that if we initialize symbols between a
definition and its use, we'll use their positions instead of the
position of `b`.
To work around this we use `lastTreeToTyper`. We assume that stub errors
will be thrown by Typer at soonest.
The benefit of this approach is better error messages. The positions
used in them are now as concrete as possible since they point to the
exact tree that **uses** a symbol, instead of the one that **defines**
it. Have a look at `StubErrorComplexInnerClass` for an example.
This commit removes the previous infrastructure and replaces it by the
new one. It also removes the fields positions from the subclasses of
`StubSymbol`s.
- This is the commit message #5:
Keep track of completing symbols
Make sure that cycles don't happen by keeping track of all the
symbols that are being completed by `completeInternal`. Stub errors only
need the last completing symbols, but the whole stack of symbols may
be useful to reporting other error like cyclic initialization issues.
I've added this per Jason's suggestion. I've implemented with a list
because `remove` in an array buffer is linear. Array was not an option
because I would need to resize it myself. I think that even though list
is not as efficient memory-wise, it probably doesn't matter since the
stack will usually be small.
- This is the commit message #6:
Remove `isPackage` from `newStubSymbol`
Remove `isPackage` since in 2.12.x its value is not used.
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Go back to using globalError to report when a stub's info is referenced,
and only throw the MissingRequirementError when compilation really
must abort due to having a StubTermSymbol in a place where a
StubClassSymbol would have been a better choice.
This situation arises when an entire package is missing from the
classpath, as was the case in the reported bug.
Adds `StoreReporterDirectTest`, which buffers messages issued
during compilation for more structured interrogation. Use this
in two test for manifests -- these tests were using a crude means
of grepping compiler console output to focus on the relevant output,
but this approach was insufficient with the new multi-line error
message emitted as part of this change.
Also used that base test class to add two new tests: one for
the reported error (package missing), and another for a simpler
error (class missing). The latter test shows how stub symbols
allow code to compile if it doesn't the subset of signatures
in some type that refer to a missing class.
Gave the INFO/WARNING/ERROR members of Reporter sensible
toString implementations; they inherit from Enumeration#Value
in an unusual manner (why?) that means the built in toString of
Enumeration printed `Severity@0`.
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Since recently type tags have relocated to scala-reflect.jar,
meaning that they are no longer always on library classpath.
In the compiler we do have code that generates type tags, and this code
is bound to fail if scala-reflect.jar isn't there.
I though this wouldn't be a problem, because type tag materialization
is only going to be triggered by users explicitly requesting a type tag.
That's generally true, but I overlooked a corner case. Since we provide
manifest <-> type tag compatibility, manifest lookup can sometimes trigger
tag lookup, which might result in tag synthesis, which blows up like this:
http://groups.google.com/group/scala-internals/browse_thread/thread/166ce4b71b7c46bb
This commit also ensures that type tag generation/interop doesnt sneak into the
code of the libraries that don't have scala-reflect.jar on their classpath.
For details refer to the discussion at scala-internals:
http://groups.google.com/group/scala-internals/browse_thread/thread/72f6ce3010f4d8
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