Can pragma-based warning suppression reliably silence diagnostics from macro expansions?

Reliability of Pragma-Based Suppression

No, {.push warning: off.} cannot be reliably used to silence diagnostics generated by the expansion of macros or templates if the pragma is placed only around the call site. Because diagnostics are typically tied to the location where the code is defined rather than where it is instantiated, lexical suppression at the call site is ignored by the compiler for the expanded content.

Mechanism of Diagnostic Emission

In Nim, the behavior of warning suppression depends on the origin of the generated code:

• Macro/Template Call Sites: Placing a suppression pragma around a macro call does not affect warnings produced by the macro's internal logic or the code it injects, as those diagnostics are attributed to the macro's definition site.
• Generic Instantiation: Similarly, warnings produced during the instantiation of generic code are tied to the generic definition. Suppression at the instantiation point will not hide these diagnostics.
• Definition-Site Suppression: To successfully silence these warnings, the {.push warning: off.} and {.pop.} pragmas must wrap the definition of the macro or template itself.

Interaction with Compiler Flags

The effectiveness of pragma-based suppression is further constrained by global compiler settings:

Setting	Impact on Suppression
--strictDefs	Promotes certain hints to errors. Since warning: off only targets warnings/hints, these promoted errors will bypass suppression and fail the build.
Verbosity Levels	Controls the global threshold for diagnostic emission (e.g., --hint:off). This acts as a global filter but does not change the lexical scoping rules of pragmas.

Verification Steps

To verify this behavior in your current compiler version (assumed Nim 2.0+), use the following scoped test:

1. Define a macro that triggers a warning (e.g., using the warning pragma) outside of any suppressed block.
2. Wrap the call to that macro in {.push warning: off.} and {.pop.}. The warning will still appear.
3. Move the definition of the macro inside the suppressed block. The warning should now be silenced.
4. Enable --strictDefs to confirm if any suppressed hints are promoted to unsuppressible errors.

Note: Please specify if you are using a version of Nim prior to 1.6, as diagnostic reporting mechanisms for macro expansions have evolved.