Std.Core.GetConfig

[fedimser]

• Store key-value configuration map in compiler state (actually, in PassContext).
• Add Std.Core.GetConfig to access config value stored inside compiler state (actually it's stored in PassContext.
  • It must be in Std.Core so we can refer to it in HIR pass.
• Add HIR transformation pass ConfigInline to relaceGetConfig(key, default) with a literal
  • If key is found, replaces call with found value.
  • Otherwise replaces with default.
  • Only supports 4 types (string, int, bool, double).
  • Error if stored or default value has type other than these 4 types, or when stored value has different type than default. This guarantees, for example, that GetConfig("key", 1) will not be replaced with a String value if config has {'key": "1"}.
  • Also require that both key and default value are literals.
• Add Python API to set config:
  • Config must be set by passing Python dict to Context constructor. if not passed, assumed empty dict.
  • Deliberately not supported in qsharp.init.
  • Once Context is created, it's immutable. To use different config value, new Context must be created. This makes it valid for GetConfig to be a function, not operation.
  • This is propagated from Python to Rust by calling Interpreter.set_config_value for each value. This still allows to mutate config when using Rust API directly (or when using Python API and using undocumented private methods). This can be strengthened by changing Interpreter to take FxHashMap<Rc<str>, Value> as constructor argument. This will require updating few more files than the current solution.
• Tests:
  • Unit tests for rule.
  • Interpreter tests (in compiler/qsc/src/interpret/tests.rs) using simulator, including tests for all possible errors.
  • One QIR generator test to make sure the GetConfig is inlined in QIR. This single test takes 3 seconds to run. However, We we have 24 qirgen tests, each taking 3-6 seconds to run - meaning qirgen tests are slow.

Questions:

• Should I change API of Interpreter (in Rust) to take the config map in constructor?
• Should I fold QIRgen test into one of existing QIRgen tests or +3 seconds increase in test time is ok? I owuld like to have at least one test checking GetConfig with QIR.

Example:

import qdk
context = qdk.Context(qsharp_config={"experiment_name": "baseline", "shots": 1000})
assert context.eval('Std.Core.GetConfig("experiment_name", "")') == "baseline"
assert context.eval('Std.Core.GetConfig("shots", 100)') == 1000
assert context.eval('Std.Core.GetConfig("noise_level", 0.01)') == 0.01

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 04414f1

Test	This Branch	On Main	Difference
compile core + standard lib	26677907 bytes	26677875 bytes	32 bytes