Do not render empty code choosers on generated index page

[guineveresaenger]

This pull request does the following:

1. Prevents the generation of code choosers with empty content
2. Writes a YAML config file with no code choosers if the example is config-only
3. Checks the pclExample object for empty pulumi YAML or PCL explicitly and before attempting to convert, removing the empty string check from the converter functions
4. Adds tests to illustrate all four situations:
   • valid provider config + example
   • invalid code
   • valid provider config but no example
   • valid example but no provider config
5. Adds exampleUnavailable placeholder constant for use when conversion fails on an individual language
6. Adds a successfulConversion flag that flips to True as soon as any one language registers as having content other than the exampleUnavailable message. The idea is that if even only one pulumi language converted, we want to display the code chooser.

Fixes #2819

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 8 lines in your changes missing coverage. Please review.

Project coverage is 68.67%. Comparing base (c158e94) to head (eb4af28).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/tfgen/convert_cli.go	0.00%	3 Missing and 1 partial ⚠️
pkg/tfgen/installation_docs.go	92.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2822      +/-   ##
==========================================
+ Coverage   68.65%   68.67%   +0.02%     
==========================================
  Files         325      325              
  Lines       41537    41578      +41     
==========================================
+ Hits        28516    28553      +37     
- Misses      11418    11419       +1     
- Partials     1603     1606       +3     

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[iwahbe]

checkExamplesEmpty isn't a super clear name. Could we change the signature to:

Suggested change

	func checkExamplesEmpty(contentStr string) bool {
	// isMdSectionEmpty returns true if there is a section titled with `title` and the section had no other content.
	func isMdSectionEmpty(title string, content []byte) bool {

Also, let's operate on []byte instead of strings, since that's what goldmark uses.

[iwahbe]

Instead of converting to text and then checking if nothing came out, can we do this with a more structured check:

A section is empty if it has one child (the title). We can then get the content of the title and validate that.

[iwahbe]

3 nits:

1. Let's operate in []byte space (instead of string) space as much as possible, since that's what goldmark uses.
2. Postfixing a variable name by its type should be avoided if possible.
3. Let's favor returning early if possible.

Suggested change

	func removeEmptyExamples(contentStr string) (string, error) {
	if checkExamplesEmpty(contentStr) {
	mybytes, err := SkipSectionByHeaderContent([]byte(contentStr), func(headerText string) bool {
	return headerText == "Example Usage"
	})
	contentStr = string(mybytes)
	return contentStr, err
	}
	return contentStr, nil
	}
	func removeEmptyExamplesSection(content []byte) ([]byte, error) {
	const title = "Example Usage"
	if !isMdSectionEmpty(title, content) {
	return content
	}
	isExamplesSection := func(s string) bool { return title == s }
	return SkipSectionByHeaderContent(content, isExamplesSection)
	}

[iwahbe]

It looks like the example was translated. Do we need a more invalid example?

[iwahbe]

I thought a goal of this PR was to remove empty ## Example Usage sections like this.

[guineveresaenger]

Yes! This test is only for the code conversion. We would still have an empty Examples section after code conversion.