Make RULE matching insensitive to eta-expansion

This is a new MR for #19790 (closed), focusing just on RULES

This patch fixes #19790 (closed) by making the rule matcher do on-the-fly eta reduction. See Note [Eta reduction the target] in GHC.Core.Rules

Other things in here

• I found I also had to careful about casts when matching; see Note [Casts in the target] and Note [Casts in the template]

• I made eta-reduction conditional on sm_eta_expand, in GHC.Core.Opt.Simplify.Utils.mkLam; reasons explained in Note [Casts and lambdas] in that module.

• Lots more comments and Notes in the rule matcher

mentioned in merge request !5658 (closed)

mentioned in merge request !6197 (closed)

added 2 commits

• 9cd9f699 - Make RULE matching insensitive to eta-expansion
• be8f34b4 - Fix a subtle scoping error in simplLazyBind

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added 18 commits

• be8f34b4...5f3991c7 - 16 commits from branch master
• 5da0e6e5 - Make RULE matching insensitive to eta-expansion
• cc02d801 - Fix a subtle scoping error in simplLazyBind

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And that match will succeed. Or am I missing something?

I think you are missing something. It's this: you say:

where we don't rename in e.

but in fact we do rename e in because we return a renv which does so. (Only lazily.)

I've updated the comments to make this clearer, I hope -- would you like to check?

Thanks, that's much clearer!

added 2 commits

• a5de5ded - Make RULE matching insensitive to eta-expansion
• 29f7b427 - Fix a subtle scoping error in simplLazyBind

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added 47 commits

• 29f7b427...f27dba8b - 43 commits from branch master
• e1808496 - Simplify and improve the eta expansion mechanism
• e8003e6d - Improve performance of eta expansion
• ca6ebd6c - Fix a subtle scoping error in simplLazyBind
• 69331402 - Make RULE matching insensitive to eta-expansion

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added 25 commits

• 69331402...4a2ef3dd - 24 commits from branch master
• 349303e5 - Make RULE matching insensitive to eta-expansion

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