internal/lsp/source: improve completion of printf operands

We now rank printf operand candidates according to the corresponding
formatting verb. We follow what fmt allows for the most part, but I
omitted some things because they are uncommon and would result in many
false positives, or didn't seem worth it to support:

- We don't prefer fmt.Stringer or error types for "%x" or "%X".
- We don't prefer pointers for any verbs except "%p".
- We don't prefer recursive application of verbs (e.g. we won't prefer
  []string for "%s").

I decided against sharing code with the printf analyzer. It was
tangled somewhat with go/analysis, and I needed only a very small
subset of the format parsing.

I tweaked candidate type evaluation to accommodate the printf hints.
We now skip expected type of "interface{}" when matching candidate
types because it matches everything and would always supersede the
coarser object kind checks.

Fixes golang/go#40485.

Change-Id: I6440702e33d5ec85d701f8be65453044b5dab746
Run-TryBot: Muir Manders <>
TryBot-Result: Gobot Gobot <>
Reviewed-by: Robert Findley <>
6 files changed
tree: be87b9f4a3777a849360109f04ec1e8c52992982
  1. .gitattributes
  2. .gitignore
  3. .prettierrc
  10. benchmark/
  11. blog/
  12. cmd/
  13. codereview.cfg
  14. container/
  15. cover/
  16. go.mod
  17. go.sum
  18. go/
  19. godoc/
  20. gopls/
  21. imports/
  22. internal/
  23. playground/
  24. present/
  25. refactor/
  26. txtar/

Go Tools

This subrepository holds the source for various packages and tools that support the Go programming language.

Some of the tools, godoc and vet for example, are included in binary Go distributions.

Others, including the Go guru and the test coverage tool, can be fetched with go get.

Packages include a type-checker for Go and an implementation of the Static Single Assignment form (SSA) representation for Go programs.


The easiest way to install is to run go get -u You can also manually git clone the repository to $GOPATH/src/

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The version of prettier used is 1.18.2.

It is encouraged that all JS and CSS code be run through this before submitting a change. However, it is not a strict requirement enforced by CI.

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