My project had succeeded in using ESP32 with the ESP IDF (and some Arduino modules included). Adding some new code (for SPIFF) gave me compile error of an undefined function. Looking further, I found that Espressif had updated the IDF to version 1.0.1.  I installed that, and saw that it showed up in the Visual Micro explorer as expected (Board Platform Installer, All Platforms, esp32, Version 1.0.1).

Now, the toolchain seems broken. Before, I had discovered a way to use ESP IDF in Visual Studio (here: https://esp32.com/viewtopic.php?t=5859) and was using that as my project template.

Now, when I build this simple blink example, I get an error which seems to indicate that esptool has been updated to identify which chip (esp8266, esp32, etc), but the board definition is using the old version of esptool. Here is the last part of the compile:

## recipe.objcopy.eep.pattern
s/gen_esp32part.exe" -q s/partitions/default.csv" tmp.ino.partitions.bin"
## recipe.objcopy.hex.pattern
ptool.exe" --chip esp32 elf2image --flash_mode "dio" --flash_freq "80m" --flash_size "4MB" -o tmp.ino.bin" tmp.ino.elf"
error: Invalid argument or value after --chip (argument #2)

Program tmp size: 169,680 bytes (used 13% of a 1,310,720 byte maximum) (10.25 secs)
Minimum Memory Usage: 13304 bytes (4% of a 327680 byte maximum)
 
# Export compiled binary to 'Project>Property Pages>Output Directory'
# Destination: file:///C:/Users/marke/source/repos/tmp/Debug/tmp.ino.doitESP32devkitV1.bin

Export Binary: Binary not found. The board definition is incorrect. mp.ino.bin
# Copy build result to 'Project>Property Pages>Intermediate Directory'
# Destination: file:///C:/Users/marke/source/repos/tmp/tmp/Debug/

Is there a new board definition (mine is DOIT ESP32 DEVKIT V1)? 
Thanks a lot for your help. I'm really stuck.

After unchecking that box, I'm still getting this result:

## recipe.objcopy.hex.pattern
ptool.exe" --chip esp32 elf2image --flash_mode "dio" --flash_freq "80m" --flash_size "4MB" -o tmp.ino.bin" tmp.ino.elf"
error: Invalid argument or value after --chip (argument #2)

Program tmp size: 169,680 bytes (used 13% of a 1,310,720 byte maximum) (7.43 secs)
Minimum Memory Usage: 13304 bytes (4% of a 327680 byte maximum)
 
# Export compiled binary to 'Project>Property Pages>Output Directory'
# Destination: file:///C:/Users/marke/source/repos/tmp/tmp/tmp.ino.doitESP32devkitV1.bin

Export Binary: Binary not found. The board definition is incorrect. mp.ino.bin

Hi Tim. Very confusing. As I said, my problems began just after installing ESP 32 IDF 1.0.1 (update to the already-installed 1.0.0). I don't know what I did, aside from adding another URL to the list of board URLs and restarting a couple of times, but now this example (here: https://esp32.com/viewtopic.php?t=5859) is building and uploading correctly. Where before (as you see above) it had been using for the bin creation updated parameters but old version of esptool:

## recipe.objcopy.hex.pattern
C:\Users\marke\AppData\Local\arduino15\packages\esp8266\tools\esptool\0.4.12/esptool.exe" --chip esp32 elf2image --flash_mode "dio" --flash_freq "80m" --flash_size "4MB" -o  <...etc> 

Now it is using (referencing updated esptool, and proper parameters):
## recipe.objcopy.hex.pattern
"C:\Users\marke\AppData\Local\arduino15\packages\ esp32\tools\esptool\2.3.1/esptool.exe" --chip esp32 elf2image --flash_mode "dio" --flash_freq "80m" --flash_size "4MB" -o  <...etc>

So now, the correct (newest) esptool is being used.

<><><>
New question: I have not discovered a way to select which version of the ESP IDF (1.0.0 or 1.0.1) I would like the project to use.  I'll post that question separately.

To install ESP IDF v1.0.1 I followed instructions here: https://docs.espressif.com/projects/esp-idf/en/latest/get-started/ (for WIndows)

Following that, it showed up in the Visual Micro explorer as expected (Board Platform Installer, All Platforms, esp32, Version 1.0.1). I don't think it was available to choose beforehand.